REESE [BRARY UNIVERSITY OF CALIFORNIA. , i8i)J. . Class No. & - W'^^^^^^^: mm A COMPLETE TREATISE ON THE ELECTRO-DEPOSITION OF METRLS. COMPRISING ELECTRO-PLATING AND GALYANOPLASTIC OPERATIONS, THE DEPOSITION OF METALS BY THE CONTACT AND IMMERSION PROCESSES, THE COLORING OF METALS, THE METHODS OF GRINDING AND POLISHING, AS WELL AS DESCRIPTIONS OF THE ELECTRIC ELEMENTS, DYNAMO-ELECTRIC MACHINES, THERMO-PILES, AND OP THE MATERIALS AND PROCESSES USED IN EVERY DEPARTMENT OF THE ART. TRANSLATED FROM THE GERMAN OF DR. GEORGE LANGBEIN, PROPRIETOR OF A MANUFACTORY FOR CHEMICAL PRODUCTS, MACHINES, APPARATUS, AND UTENSILS FOR ELECTROPLATERS AND OF AN ELECTRO-PLATING ESTABLISHMENT, IN LEIPZIG. WITH ADDITIONS BY WILLIAM T. BRANNT, EDITOR OF "THE TECHNO-CHEMICAI^ RECEIPT BOOK." THIRD EDITION, THOROUGHLY REVISED AND MUCH ENLARGED. ILLUSTRATED BY ONE HUNDRED AND FIFTY ENGRAVINGS. PHILADELPHIA : HENRY CAREY BAIRD & CO., INDUSTKIAL PUBLISHEKS, BOOKSELLEKS, AND IMPOETEKS. 810 WALNUT STREET. 1898. COPYRIGHT BY HENEY CAEEY BAIKD & CO., 1898. 7V 7*? PRINTED AT THE WICKERSHAM PRINTING HOUSE, 53 and 55 North Queen Street, LANCASTER, PA., U. S. A. PREFACE TO THE THIRD BMERICflN EDITION. THE rapid sale of the second American edition of Dr. George Langbein's work, " Handbuch der Galvanischen Metall-Nieder- schlaege" and the constant demand for it, are the best proofs of the value and usefulness of the book. In the third edition, which is now presented to the public, no changes have been made in the arrangement of the text, and it has been endeavored to include all practical methods of plat- ing metals which have become known since the publication of the first and second editions, as well as the most recent ma- chinery and apparatus, so as to make the work still more ac- ceptable and useful to the reader. The editor is under obligations for information and electro- types to the Hanson & Van Winkle Co., of Newark, N. J., the well-known firm dealing in electro-platers' supplies ; to the Electro- Chemical Storage Battery Co., of New York City, and to Mr. Bossard, inventor of the Bossard Mechano-Electro- plating. Tanks. The publishers have spared no expense in the proper illus- tration and the mechanical production of the work, and, like the previous editions, it has been provided with a copious table of contents and a very full index, so as to render reference to any subject prompt and easy. W. T. B. PHILADELPHIA, February I, 1898. (Hi) PREFACE TO THE FIRST flMERICAN 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, Vollsiaendiges Handbuch der Galvanise hen Metall- Niederschlaege, is presented to the English-reading public with the full confidence that it will not only fill a useful place in technical literature, but will also prove a ready book of reference and a practical guide for the workshop. In fact, it is especially intended for the practical workman, wherein he can find advice and information regarding the treatment of the objects while in the bath, as well as before and after electro-plating. The au- thor, Dr. George Langbein, is himself a master of the art, being the proprietor of an extensive electro-plating establishment combined with a manufactory of chemical products, machinery and apparatus used in the industry. The results yielded by the modern dynamo-electric machines, to which the great advance in the electro-plating art is largely due, are in every respect satisfactory, and the more so since the need of accurate, and at the same time handy, measuring in- struments has also been supplied. With the assistance of such measuring instruments, the establishment of fixed rules regard- ing the current-conditions for a galvanic bath has become pos- sible, 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 deter- (v) VI PREFACE TO THE FIRST AMERICAN EDITION. mined conditions and provided with well-working measuring instruments, he can at once produce beautiful and suitable de- posits of the various metals. The data referring to these current-conditions, according to measurements by Dr. Langbein, are given as completely as pos- sible, while for the various baths, only formulae yielding entirely reliable results have been selected. To most of the baths a brief review of their mode of action and of their advantages for certain uses is added, thus enabling the operator to select the bath most suitable for his special purpose. To the few formulae which have not been tested, a note to that effect is in each case appended, and they are only given with due reserve. To render the work as useful as possible, the most suitable formulae for plating by contact and immersion, as well as the best methods for coloring the metals, and the characteristic properties of the chemicals used in the industry, are given. However, the preparation of the chemicals has been omitted, since they can be procured at much less expense from chemi- cal works than it would be possible for the electro-plater to make them in small quantities, even if he possessed the neces- sary apparatus and the required knowledge of chemistry and skill in experimenting. If is hoped that the additions made here and there by the translator, as well as the chapter on " Apparatus and Instru- ments," and that of " Useful Tables," added by him, may con- tribute to the usefulness of the treatise. Finally, it remains only to be stated that the publishers have spared no expense in the proper illustration and the mechani- cal 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 i, 1891. CONTENTS HISTORICAL PART. CHAPTER I. HISTORICAL REVIEW OF ELECTRO-METALLURGY. PAGK 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, f the true causes of the electric-contact current; Galvani's experiments . . I 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 ; Cruikshank's trough battery . . ... . . . . . . . .2 Decomposition of water by electrolysis by Nicholson and Carlisle, 1800 ; Wollaston's observations, 1801 ; Cruikshank's investigations, 1803 ; Brugnatelli's experiments in electro-gilding, 1805 ; Sir Humphrey Davy's discovery of the metals potassium and sodium, 1807 ; Prof. Oersted's discovery of the deflection of the magnetic needle, 1820 . 3 Construction of the galvanoscope or galvanometer; Ohm's discovery, in 1827, of the law named after him ; Faraday's discover} 7 , in 1831, of electric induction ; First electro-magnetic induction machine con- structed by Pixii; Faraday's electrolytic law laid down and proved in 1833 ! Production of iridescent colors, in 1826, by Nobili ; Production of the amalgams of potassium and sodium, in 1853, by Bird ; Discov- ery of the actual galvano-plastic process, in 1838, by Prof. Jacobi . 4 Claims of priority of invention by Mr. T. Spencer and Mr. C. J. Jordan ; I/abors* of the Elkingtons and of De Ruolz ; Murray's discovery in 1840, of black-leading; Introduction, in 1843, f gutta-percha by Dr. Montgomery; First employment, in 1840, of alkaline cyanides by Wright . 5 Patent for the deposition of nickel, 1840 ; Origination of the term Vlll CONTENTS. "electro-metallurgy," by Mr. Alfred Smee, 1841 ; Prof. Boettger's dis- covery, in 1842, of the deposition of nickel from its double salt ; First deposition of metallic alloys by De Ruolz ; First use of thermo- electricity, in 1843, by Moses Poole ; Advances in the art of electro- deposition ....... ..... The first magnetic machine that deposited silver on a practical scale, constructed, in 1844, by Woolrych ; Attempts, since 1854. by Christofle & Co. to replace their batteries by magneto-electrical machines ; The Alliance machine ........... Objections to Wilde's machine ; Dr. Antonio Pacinotti's invention, in 1869, of the ring named after him ; Siemens' dynamo machine, 1866 ; Wheatstone's dynamo machine, 1867 ; Introduction, in 1871, of Zen- obe Gramme's machine ; The Hefner-Alteneck machine, 1872 ; Sie- mens & Halske's machine, 1884; S. Schuckert's machine, 1884; Vari- ous dynamo-electrical machines . . . . . . . Investigators and practitioners who have contributed to the improve- ment of the electro-chemical processes and the perfection of galvano- plasty . . . . II. THEORETICAL PART. CHAPTER II. MAGNETISM AND ELECTRICITY. i. MAGNETISM. Loadstone or magnetic iron ore ; Natural and artificial magnets ; Defi- nitions of the magnetic poles and of the neutral line or neutral zone, and their positions . . . . . . . . . . .10 Magnetic meridian ; North and south poles ; Phenomena of attraction and repulsion; Ampere's theory . . . . . . . .11 The solenoid ; Rejection of Ampere's theory by many scientific men ; Definition of the magnetic field 12 II. ELECTRICITY. Definition of idio-electrics and non-electrics; Gray's discovery, 1727; Good and bad conductors; The electroscope; Existence of two kinds of electricity ; Vitreous, or positive, and resinous, or negative, elec- tricity 13 CONTENTS. ix PAGE Double fluid hypothesis of electricity ; Single fluid hypothesis of elec- tricity . . . . ... . . . . . .14 Investigations of Prof. Herz, 1889 ; Colomb's law ; Series of electro- motive force or tension ; Production of electricity by the contact of metals and fluids ........... 15 The galvanic current or hydro-electric current ; Galvanic element or galvanic chain; Electrical potential; Electro-motive force; Resistance. 16 Conductivity of metals according to Lazere Weiler; Quantity of current Ohm's law 17 Essential or internal resistance; Non-essential or external resistance . 18 Union or coupling of the elements for electro-motive force or tension ; Coupling for quantity of current ; Mixed coupling . . . .20 Proposition deduced from Ohm's law; Effects of the electric current . 21 Electro-magnetism. Rule for determining the direction which the magnetic needle will as- sume when placed in any particular position to the conducting wire . 21 Galvanoscopes, galvanometers, or multipliers; The astatic galvanome- ter ; The tangent galvanometer ; The sine galvanometer . . .22 Electro-magnets ; The solenoid ; Law of the action of two electrified wires on each other . . . .... . . . .23 Induction. What is understood by induction . '. * . . . . .23 Primary or inductive current ; Secondary or induced current . . .24 Alternating currents ; Extra currents . 25 Chemical Actions of the Electric Current Electrolysis. Reduction of the constituents of a fluid by the electric current ; Pure water a bad conductor . . . . . . . . . .25 Faraday's discovery of the chemical actions of the electric current ; Electrolysis ; Electrolyte ; Electrodes ; Anode ; Cathode ; Ions ; Ani- ons ; Cations ; Atoms ; Clausius' theory of the molecules . . .26 Counter or polarizing current; Faraday's electrolytic laws ; Experi- ments with the voltmeter . .27 Local action ; Electro-chemical equivalents ; Joule's law . . .29 Consumption of power in electrolysis ; Electric units adopted by the International Congress of 1881 ; Fundamental or C. G. S. (centimetre- gramme-second) system ; Force or power dyne ; Work erg ; Quan- tity ; Potential or electro-motive force ; Resistance . . . .30 The ohm ; The ampere ; The volt ; The farad ; The coulomb ; The watt; Definition of the English and of the French horse-power . .31 CONTENTS. SOURCES OF CURRENT. CHAPTER III. GALVANIC ELEMENTS THERMO-PILESMAGNETO- AND DYNAMO- ELECTRIC MACHINES. A. GALVANIC ELEMENTS. The voltaic pile ; Trough battery 32 Reduction of local action by amalgamating the zinc ; Various ways of amalgamation ............ 33 Bruant's recommendation ; Definition and cause of polarization ; Smee's element . .',-... . . . . . . . .34 Constant elements ; Daniel's element ....... 35 Meidiuger element . .36 Grove element ; Bunsen elements 37 Improved Bunsen cell .......... 39 Electropoion and its composition ; Location of elements ; Dupre"'s sub- stitute for sulphuric and nitric acids for filling elements . . .40 A soluble chromium combination which depolarizes with rapidity ; In spection and cleansing of the binding screws . . . . .41 Manipulation of Bunsen elements ........ 42 Advisability of having a duplicate set of porous clay cells ; Renewal of the acids; Foote's pinnacle gravity battery 43 Oppermann's element .......... 44 The I/eclanche element; Lallande and Chaperon element . . .48 The cupron element . . . . . . . . . . .50 Various elements ; Duns' potash element ....... 51 Element patented by Knaffe and Kiefer, of Vienna 52 Plunge or bichromate batteries ; The Bunsen plunge battery ; Fein's bichromate battery ........... 53 Keiser & Schmidt's bichromate battery 54 Bichromate element for gilding or silvering small articles . . .55 Stcehrer's battery ; Plunge battery manufactured by Dr. G Langbein & Co .56 B. THERMO-ELECTRIC PILES. Prof. Seebeck's discovery, in 1822, of a new source of electricity . . 57 Definition of a thermo-electric couple and of thermo-electricity; Noe's thermo-electric pile ; Clatnond's thermo-electric pile .... 58 Hauck's thermo-electric pile ......... 59 Gulcher's thermo-electric pile ......... 60 Superiority of dynamo-electric machines over thermo-electric piles . 62 CONTENTS. xi C. MAGNETO- AND DYNAMO -ELECTRIC MACHINES. Faraday's discovery, in 1831 ......... 62 Magnetic field, or the region of the lines of force ; What a magneto- electric or dynamo-electric machine actually is . . . .63 Prof. S. P. Thompson's definition of a dynamo-electric machine * . 64 Pixii's electrical machine, 1832 ; Saxton and Clarke's improvements ; Dr. W. Siemens' improvement, 1857; Pacinotti's ring conductor, 1860; Dr. W. Siemens' and Sir. C. Wheatstone's discovery . . . .65 Classes of electric generators ; Continuous current and alternating cur- rent machines ; The Gramme machine ....... 66 The Gramme armature ; Modern Gramme dynamo for galvanoplastic purposes ............. 67 Disadvantage of the Gramme machine ....... 68 S. Schuckert's flat ring machine 69 Fein's dynamo machine ; The Brush dynamo 70 The ring of the Brush dynamo ......... 71 Siemens' and Halske's dynamo-electric machines . . . . .72 Krcettlinger dynamo ........... 74 Lahmeyer dynamo 75 Resume of the evolution of the dynamo for plating purposes in the United States ; The Weston dynamo 77 "Little Wonder" dynamo - . . . . .78 The "H. & V. W." dynamo . . . . . . . . . 79 The new "H. & V. W." dynamo . . , . . . . .81 Advantages claimed for the new " H. & V. W." dynamo ; Various dynamo machines . . . . 83 Value of the dynamo, and its effect upon the electro-plating industry ; Data for the most suitable machine . . . * . . 84 IV. PRACTICAL PART. CHAPTER IV. ARRANGEMENT OF ELECTRO-PLATING ESTABLISHMENTS IN GENERAL. Necessity of sufficient light and thorough ventilation . . . .85 Location of Bunsen elements; Provision for heating . . . .86 Importance of a good supply of water; Best materials for floors; Size of the operating room .87 Grinding and polishing rooms . . . . ... , . 88 Prevention of dust in the polishing room; Location of the transmission carrying the belt-pulleys . . . . . .,-..,, . . 89 Xll CONTENTS. ELECTRO-PLATING ARRANGEMENTS IN PARTICULAR. Parts constituting the actual electro-plating plant ; Arrangement with elements ........*..-.. 89 Choice of coupling the elements; Proportion of the effective zinc surface of the elements to that of the anodes and articles . . . .90 Requisites as regards the result of the process of deposition . . .91 Coupling of elements for solid and thin deposits . . . . .92 Auxiliary apparatus; The rheostat, current-regulator, resistance board or switch board .93 Conditions upon which the action of the resistance board is based . . 94 Horizontal and vertical galvanometers . . . . . . .95 Location of the resistance board and galvanometer ; Improved switch- board or rheostat . . . . ... . . . .96 Indications made by the galvanometer 97 The Weston voltmeter . 100 The Weston ammeter; Rules to be observed in conducting the current . 102 Positive or anode wire; Negative or object wire; Vats or tanks . . 103 Wooden vats; Wooden vats lined with sheet lead 104 Enameled iron vats; Agate vessel for gold and other solutions . .105 Conducting rods; Anodes and their arrangement ..... 106 Binding posts and screws; Mode of suspending the anodes . . . 107 Mode of suspending the objects; Slinging wires; Protection of the con- ducting rods; Cleansing and rinsing apparatuses ..... 108 Dipping or pickling ; Sawdust ; Arrangements with dynamo-electric machines ; Rules for setting-up and running dynamo-electric machines ............ 109 Insulation of the object and anode wires ; Special wire carriers ; Ar- rangement with one machine which has to feed several baths; Loca- tion of the dynamo resistance-board . ..... 110 The amperemeter or ammeter; The voltmeter 113 Coupling of the main object wire with the main anode wire, with the re- sistance board, the voltmeter, the shunt, and the two baths . . 114 Ground plan of an electro-plating establishment . . . . .116 Table for freeing the articles from grease . . . . . .119 Plating room arranged by the Hanson & Van Winkle Co., of Newark, N. J. ; Mode of calculating the thickness of conducting wire for dynamos ............. 120 CHAPTER V. TREATMENT OF METALLIC ARTICLES. A. MECHANICAL TREATMENT. Treatment before electro-plating ; Scratch brushing ; Formation of the deposit in correspondence with the surface of the basis-metal . . 122 Modes of scratch-brushing ; Various forms of scratch brushes . . 123 \ CONTENTS. xiii Treatment of scratch-brushes ; Circular scratch-brushes .... 124 Circular scratch-brush for cleansing purposes, and its construction . 125 Brushes . . -. ' . . . . . ... . . 126 Cleansing by the sand blast . . ... . . . . 127 Tumbling drum or box ..*'.. . . . . . . . 128 Improved exhaust tumbling barrel . .... . . . . 129 Mode of polishing articles in the tumbling drum ..... 130 Grinding; Grinding disks and their construction; Roughing wheel, medium wheel and fine wheel 4 . . . . . . . . 132 Treatment of the grinding disks ; Vienna lime ; Grinding lathes . . 133 Execution of grinding ' . . . . . . , . . 134 Fibres and fibre-brushes ; Grinding iron and steel articles . . . 135 Grinding brass and copper castings ; Treatment of sheets of brass, Ger- man silver, and copper ; Treatment of zinc castings and sheet zinc . 136 Polishing; Foot lathe for polishing ; " Compress " polishing wheels . 137 Foot lathe for light grinding, polishing and buffing. . . . . 138 American double-polishing lathe; Lathe manufactured by the Hanson & Van Winkle Co., of Newark, N. J. .... . . . .139 Glue pot .... . . ... . . . -. . 141 Belt strapping attachment or endless belt machine . ., 142 Flexible shaft for grinding, polishing and buffing . . . . . 143 Polishing materials ; Rouge composition ; Burnishing . . . . 144 Mechanical treatment during and after the electro-plating process ; Scratch-brushing the deposits , . . . ..... 145 Effect of scratch-brushing ; Scratch-brushes used for different metals ; Decoctions used in scratch-brushing ; Scratch-brushing by hand . 146 Lathe brush. ............ 147 Treatment of the finished electro plated objects; Sawdust for drying the objects ; Method of freeing nickeled objects from moisture . . . 148 Polishing deposits of nickel, copper, brass, tin, gold and silver, and platinum; Operation of burnishing and forms of burnishers . . 149 B. CHEMICAI, TREATMENT. Pickling ; Mixture for pickling cast iron and wrought iron objects . 150 Excellent pickle for iron ; To cleanse badly-rusted iron objects ; Dura- tion of pickling ; Pickling zinc objects ; Cleansing and brightening copper, brass, bronze, tombac, and German silver . . - . . 151 Preliminary pickle ; Bright dipping bath ; Use of potassium cyanide for pickling; Manipulation of pickled objects 152 Preparation of a good dead dip ; Main points in pickling . ... . 153 Absorbing plant for escaping acid vapors . . . . . . . 154 Regaining of acid and metal from exhausted dipping baths -. . 155 Mixture for the production of a grained surface ; Removal of grease . 156 Preparation of lime mixture ; Cleansing with benzine .... 157 Tying the objects to metallic wires; Removal of oxide from the metallic objects; Steel spring carboy rocker . . . . . . .158 xiv CONTENTS. PAGE CHAPTER VI. PROCESSES OF ELECTRO-DEPOSITION. Importance of the constitution of the water used as a solvent; Spring and well water; Rain water . . ...... 159 Importance of the purity of the chemicals used . . . .160 Concentration of the baths; Non-reliability of measurement by hydro- meter degrees 161 Effects of baths too poor in metal and too concentrated; Stirring up the baths 162 Effect of heavier and more saturated fluid on the anodes; Constant agitation of the baths by mechanical means ...... 163 Temperature of the baths; Boiling of the baths; Kettles and boiling pans ............. 164 Working the bath with the electric current in place of boiling; Dissolu- tion of nickel salts dissolving with difficulty . . . . . . . 165 Filtration of the boiled solutions; Means of securing lasting qualities to the baths; Choice of anodes . . ; 166 Alloying of the deposit with the basis-metal; Gore's experiments; Con- ditions for the good performance of an electrolytic bath . . .167 Reduction of metals without a battery (electro-deposition by contact); Reduction of metal by dipping one metal into one fluid . . .168 CHAPTER VII. DEPOSITION OF NICKEL AND COBALT. i. NICKELING. Growth and popularity of nickel-plating; Properties of nickel . .169 Nickel baths; General rules for preparing nickel baths . . . .170 The active constituent in many prepared nickeling salts; Use of the chlorine combinations; Additions to the nickeling bath recommended by various experts; Effects of the presence of small quantities of a free acid; Boric acid as an addition to nickeling and all other baths, and its effects 171 Determination of the acidity, alkalinity, and neutrality of nickel baths . 172 Formulae, preparation, characteristics and treatment of nickel baths . 173 Burning or over-nickeling . . . T . . . . . . 174 Nickel baths containing boric acid; Weston's bath ..... 175 Kaselowsky's formula 176 Proportion of cast to rolled anodes . . 177 Bath for rapid nickeling of polished, slightly coppered zinc articles; Nickel bath for iron, brass and copper, and sheet zinc and zinc castings .... 178 Compositions of a few nickel baths which have been highly recom- CONTENTS. XV PAGE meiided; An English formula; Addition of bisulphide of carbon to nickel baths; Bath for nickeling small articles ..... 179 Nickel baths without nickel salts; Nickel anodes 180 Objections to insoluble anodes ......... 181 Use of rolled and cast anodes together in one bath; Size of anode- surface 183 Cause of the reddish tinge of the anodes; Manner of suspending the anodes; The process of electro-nickeling ...... 184 Coppering or brassing articles previous to nickeling .... 185 Suspension of the objects in the bath; Suitable current-strength for nickeling 186 Burning or over-nickeling ; Criteria for judging whether nickeling pro- gresses with a correct current-strength ....... 187 Most suitable current-density for nickeling ...... 188 Solid nickeling ; Test for sufficient!}' heavy nickeling .... 189 Arrangement of the anodes ; Nickeling of flat objects ; Round or half- round surfaces ; Smooth articles ; Objects with depressions and hol- lows, and lamp feet of cast zinc ........ 190 Additional rules for nickeling and other electro-plating processes; Mode of suspending objects with depressions and hollows in the bath; Polar- izing phenomena .. ...... . . . . . . 191 Nickeling en masse of small and cheap objects ..... 193 Warren's solutions of nickel and of cobalt to be decomposed in a sim- ple cell apparatus; Stripping nickeled articles ...... 194 Stripping acid . . . . . . . . . . . 195 Stripping by means of the battery or the dynamo; Remedy against the yellowish tone of nickeling ; Resume of the principal phenomena which may occur in nickeling . . . . . . . . 196 Refreshing nickel baths . . . .198 Polishing nickel deposits ; Treatment of nickeled articles which are to be left dead; Nickeling sheet zinc ; Mystery with which the nickeling of sheet zinc has been surrounded 199 Conditions required for, and the execution of nickeling sheet zinc ; Pre- liminary grinding or polishing ; Construction of cloth bobs . . 200 Mode of polishing or grinding the sheets . ....'. . 201 Self-acting sheet polishing machines ; F. Rauber's sheet grinding and polishing machine . . . . 202 Freeing the sheets from grease . ...... . . 204 Nickeling the sheets ; Advantage of previous coppering or brassing . 205 Prevention of the peeling off of the nickel deposit ; Coppering the sheets . . . . 206 Dimensions of vats for nickeling the sheets ; Proportion of anode-surface to zinc-surface . . . ... * . , ti . . <. . , . . 207 Cause of black streaks and stains ; Augmentation of the metallic content of the bath ; Polishing the nickeled sheets , r .. * .... . 208 XVI CONTENTS. PAGE Nickeling of tin-plate, of copper and brass sheets, and of sheet iron and sheet steel ' . . . ' . . .209 Nickeling of wire '. 210 Apparatus for nickeling wire; Nickeling wire gauze . . . . 212 Nickeling of knife-blades, sharp surgical instruments, etc. . . . 213 Nickeling of electrotypes, cliches, etc 214 Baths for hard nickeling . . 215 Treatment of the nickeled plates; Recovery of nickel from old baths . 210 Urquhart's plan for recovering nickel from old solutions ; To improve defective nickeling; Arrangement of the "doctor ; : ' Nickeling by contact and boiling . . . . . . ... . 217 Deposition of an alloy containing nickel according to R. Kaiser ; De- posits of nickel alloys . . . . . . . . . 219 Nickel Bronze ; French process for the deposition of German silver ; Watt's method .220 2. COBAI/TING. Properties of cobalt 221 Baths for cobalting ; Cobalting of copper plates for printing ; Determin- ation of the quantity of copper dissolved in stripping the cobalt de- posit from cobalted copper plates ........ 222 Warren's cobalt solution ; Cobalt solution recommended by Mr. G. W. Beardslee, of Brooklyn, N. Y. ; R. Daub's bath for cobalting small fancy articles 223 Cobalting by contact 224 CHAPTER VIII. DEPOSITION OF COPPER, BRASS AND BRONZE. i. COPPERING. Properties of copper; Copper baths, their composition, preparation, prop- erties and treatment .......... 225 Hassauer's copper bath; Copper baths for iron and steel articles . . 226 Baths for coppering zinc articles ........ 228 Baths prepared with cupron and cuproso-cupric sulphite; Copper baths without potassium cyanide 229 Weil's copper bath and method of coppering; Copper bath recommended by Walenn; Copper bath according to Pfanhauser .... 230 Gauduin's copper bath; Execution of coppering; Anodes used; Forma- tion of slime on the anodes ; Phenomena appearing in copper baths containing cyanide .......... 231 Necessity of careful cleaning and pickling the articles before coppering. 232 Preliminary scouring and pickling; Scratch-brushing and treatment of defective places ........... 233 CONTENTS. xvii Prevention of the formation of stains ; Schultz's patent to prevent the formation of stains; Polishing the deposit of copper .... 234 Treatment of coppered objects to be coated with another metal; Copper- ing small articles en masse; Coppering by contact and dipping . . 235 To coat zinc plates with a very thin but hard layer of copper ; Bacco's copper bath; Brush-coppering . . .' 236 Application of a thin film of copper to iron and steel objects; Coppering steel pens, needles' eyes, etc. ; Inlaying of depressions of copper art- castings . . . .......... . . . . 237 2. BRASSING (CUIVRE-POU DEPOSIT). Constitution and varieties of brass; Brass baths, their composition, pre- paration and treatment . .'.__. 238 Rules for baths containing more than one metal in solution; Brass bath according to Roseleur . . . . . . . . . . 239 Irregular working of fresh brass baths; Bffect of an addition of arsenious acid to brass baths . . .... . . . . . . 240 Baths for brassing iron; Baths with cuproso-cupric sulphite . . . 241 Bath for brassing cast iron, wrought iron and steel ; Composition of a solution for transferring any copper-zinc alloy serving as anode . 242 Bath for brassing all kinds of metal recommended by Pfanhauser; Ex- ecution of brassing .... . . - . .'.".. . 243 On what the color of the deposits depends; Anodes used and anode-sur- face required . , . . . . . . ... . 244 Formation of slime on the anodes, and what it indicates; Remedies for the slow formation of the deposit . . . . . . , . 245 Importance of the distance of the objects to be brassed from the anodes; Brassing of unground iron castings . , fc . . . . 246 Brassing by contact and dipping . . . . . . / . . 247 3. BRONZING. Gountier's solution for coating wrought and cast iron with bronze; Other bronze baths and their composition, preparation and treatment . . 247 Hess's bath for deposits of tombac; Execution of bronzing . . . 248 CHAPTER IX. DEPOSITION OF SILVER. Properties of silver ; Silver baths, their composition, preparation and treatment; Silver bath for a heavy electro-deposit of silver (silvering by weight); Preparation of bath with silver chloride .... 249 Preparation of bath with silver cyanide . . - < . , . . 250 Silver bath for ordinary electro-silvering; Treatment of the silver baths; The silver anodes^ ..... . . . ... . 251 Most suitable current-strength for silver baths; Coupling of the ele- xviii CONTENTS. PAGE ments; Indication of the presence of too much or not enough potas- sium cyanide . . ; . . . . . . . . . . 252 Objections to insoluble platinum anodes; The behavior and appearance of the anodes as criteria of the content of potassium cyanide in the bath . .... 253 Keeping the bath constant by silver anodes; Proper treatment of baths made with chloride of silver 254 Gradual thickening of the bath; Augmentation of the content of silver in baths . . . . 255 Determination of the content in proper proportions of silver and excess of potassium cyanide . . . . . . . . . . 256 Contrivances to keep the objects to be silvered in gentle motion while in the bath 257 Singular phenomenon in silvering; Remedy against a yellow tone of the silvering . ...... . . . . . . . 258 Areas silvering as introduced by the London Metallurgical Co. ; Experi- ments in areas silvering .......... 259 Execution of silvering; Silvering by weight ...... 260 Mechanical and chemical preparation of the objects; Treatment of copper and its alloys; German silver and brass; Freeing from grease; Pickling ; Rubbing ; Pickling in the preliminary pickle ; Amalgama- ting (quicking) ........... 261 Slinging wires; Treatment of the objects while being silvered; Amount of silver deposited upon various grades of plated ware manufactured by the William Rogers Manufacturing Co., of Hartford, Conn. . . 262 Method of controlling the weight of the deposit . . . . . 263 Roseleur's plating balance ......... 264 Plating balance together with the resistance board, voltmeter and silver bath ..-. 266 Treatment of articles which are to retain the crystalline dead white, with which they come from the bath; Polishing the silvered articles; Operation of burnishing; Burnishing machines ..... 267 Ordinary silvering; Practice of the Meriden Britannia Co.'s works at Meriden, Conn., with Britannia or white metal 268 Treatment of German silver or nickel articles and of steel articles; Methods in use with the William Rogers Manufacturing Co., Hart- ford, Conn., for preparing work for plating; For cleansing (steel) cntlery; Nickel-silver (German silver) for spoons; Britannia metal (hollow ware) 269 Rogers' striking solution ; Meriden Company's striking solution; Methods of depositing an extra heavy coating of silver on the convex surfaces of spoons and forks; " Stopping off " 270 Stopping of varnish; Silvering by contact, by immersion, and cold silvering with paste; Bath for silvering by contact with zinc; Baths for silvering by immersion ......... 271 CONTENTS. XIX Preparation of solution of sodium sulphide . , . . . . 272 Dr. Ebermayer's bath for immersion . , . . . . 274 Silvering articles, especially of alloys of copper without the use of a current . . ........ ..... . . . 275 Coating small articles such as hooks and eyes, pins, etc., with a thin film of silver . ! . . . . . . . . . 276 Cold silvering with paste; Composition of argentiferous pastes; Graining 277 Preparations used for graining . . . . . . . . . 278 The operation of graining; Resist and its composition .... 279 Gilding of grained watch parts; Silvering of fine copper wire . . 280 Incrustations with silver, gold and other metals ; Imitation of niel or nielled silvering; Preparation of the nielling powder .... 281 Imitation of uiel by electro-deposition; Old (antique) silvering . . 282 Oxidized silver ; Yellow color on silvered articles ; Stripping silvered articles 283 Determination of electro-deposited silvering ^ 284 Method for the determination of genuine silvering used by custom-house officers in Germany; Recovery of silver from old silver baths, etc. . 285 The wet method; Reduction of the chloride of silver by pure zinc . . 286 CHAPTER X. DEPOSITION OF Goux Occurrence and properties of gold ; General composition of the native metal ..'... . .287 Shell-gold or painter's gold; Gold baths, their composition, preparation and properties ............ 288 Bath for cold gilding . . 289 Bath with yellow prussiate of potash for cold gilding . . . . 290 Baths for hot gilding . . 291 Preparation of the gold bath with the assistance of the electric current. 292 Management of gold baths; Use* of platinum anodes for coloring the de- posit; Coloration by means of the resistance board . 293 Vats for gold baths; Porcelain dish for small gold baths for hot gilding. 294 Heating larger baths; Execution of gilding; Gilding without a battery. 295 Preparation of the articles for gilding; Current-strength for gilding . 296 Gilding the inner surfaces of hollow-ware ; Gilding in the cold bath ; Gilding with the hot bath . .297 Red gilding . . . ^ 298 Determination of the content of copper required for obtaining a beauti- ful red color; Green gilding; Rose-color gilding; Dead gilding. . 299 Dead gilding on zinc . . . . . - . . . . . . 300 Coloring of the gilding; Gilder's wax and its preparation . . . 301 Processes for giving gilded articles a beautiful rich appearance ; Mode of improving bad tones of gilding ... . . . . . 302 XX CONTENTS. PAGE Incrustations with gold ; Gilding of metallic wire and gauze; J. W. Spaeth's machine for gilding wire and gauze ..... 303 Gilding by contact, by immersion and by friction; Baths for gilding by contact 305 Porcelain capsules for dissolving gold ....... 306 Preparation of " matt " for gilded articles; Baths for gilding by dipping. 308 Gilding of porcelain, glass, etc.; Gilding by friction, or gilding with the rag, with the thumb, with the cork . . . . . . . 310 Martin and Peyraud's method of gilding by friction .... 311 Fire or mercury gilding; Preparation of the gold amalgam; Application of the amalgam . . . . . 312 Method of gilding which is a combination of fire-gilding with electro- deposition . . . . . . . . * . . . 314 Improvement of old dead gilding; Du Fresne's method of gilding; Re- moving gold from gilded articles "stripping" 315 Determination of genuine gilding . '. .... . x . . 316 Recovery of gold from gold baths, etc. ; The wet process . . .317 Recovery of gold from acid mixtures . . -...,- . . . . 318 CHAPTER XI. DEPOSITION OF PLATINUM AND PALLADIUM. I. DEPOSITION OF PLATINUM. Properties of platinum . . . . . . . " . .318 Platinum baths, their composition, preparation and properties ; Boett- ger's bath; Preparation of platoso-ammonium chloride . . .319 Platinum bath patented by the Bright Platinum Plating Co. of London; Directions for preparing platinum baths, by Dr. W. H. Wahl; Alkaline platinate bath . .320 Preparation of an oxalate solution ... .x .... 321 Preparation of the phosphate bath ; Management of platinum baths . 322 Execution of platinizing ; Platinizing of large objects ; Production of heavy deposits ............ 323 Platinizing of glass ; Platinizing by contact ; Recovery of platinum from platinum solutions .......'... 324 2. DEPOSITION OF PALLADIUM. Properties of palladium ; Palladium bath according to M. Bertrand ; Pilet's bath for plating watch movements 325 CHAPTER XII. DEPOSITION OF TIN, ZINC, LEAD AND IRON. I. DEPOSITION OF TIN. Properties of tin ; Moire" metallique on tin ....... 326 Tin baths, their composition, preparation and properties; Direct tinning of objects of zinc, copper, and brass ....... 327 CONTENTS. XXI Experiments with Salzede's bronze bath ; Pfanhauser's experiments ; Tin bath given by Taucher ... . . . . . . 328 Management of tin baths ; Current strength required ; Anodes ; Choice of tin salts 329 Preliminary treatment of iron and steel objects; Process of tinning; Tin- ning by contact and boiling ; Solutions for tinning by contact . . 330 Zilken's solution for tinning by contact in a cold bath; Tinning solution for iron and steel articles; Tinning solution for small brass and copper articles 331 Boettger's solution ; Eisner's bath ; Production of a durable coating of tin ; Tinning of needles . 332 Superficial coating of tin on articles of brass, copper or iron ; Stalba's method of tinning ........... 333 2. DEPOSITION OF ZINC. Properties of zinc. 333 Zinc baths, their composition, preparation, and properties; Difficulty In producing a deposit of uniform thickness upon shaped articles . . 334 Anodes used in zinc baths ........... 335 Execution of zincking 336 Zincking iron by contact ; To coat brass and coppar with a bright layer of zinc; Zinc alloys; Production of an alloy of zinc and tin by the use of the battery . . ... . . , . . . .- . 337 3. DEPOSITION OF I,EAD. Properties of lead; Lead baths, their composition, preparation and prop- erties; Anodes for lead baths 338 To coat gun barrels and other articles of steel or iron with superoxide of lead; Leading by contact; Metallic chromes (Nobili's rings) iridescent colors, electrochromy 339 Mr. Gassort's plan to obtain metallo-chromes . . . . . 340 4. DEPOSITION OF IRON (STEEUNG). Principal use of the electro-deposition of iron ; Steel baths, their compo- sition, preparation, and properties; Varrentrapp's steel bath ; Boett- ger's steel bath , . . .341 Baths for the production of electrotypes in iron ; Steel bath recom- mended by Klein; C. Obernetter's method of steeling copper printing plates . . . .., . . . . 342 Production of a deep black deposit of iron for decorative purposes . 343 Management of iron baths; Execution of steeling ..... 344 Steeling by contact * ... 345 XX11 CONTENTS. PAGE CHAPTER XIII. DEPOSITION OF ANTIMONY, ARSENIC, AIJJMINIUM. I. DEPOSITION OF ANTIMONY. Properties of antimony; Antimony baths, their composition, prepara- tion and properties; Explosive property of the antimony deposit . 345 Lustrous non-explosive deposit of antimony ...... 846 2. DEPOSITION OF ARSENIC. Properties of arsenic; Arsenic baths, their composition, preparation and properties . . . . 346 Deposits of antimony and arsenic by contact and immersion . . . 347 3. DEPOSITION OF ALUMINIUM. Properties of aluminium; Aluminium baths; Bertrand's process; Goze's process . 348 Reinhold's formula; New method for the electro -deposition of alu- minium . 349 Process used by the Tacony Iron & Metal Co. in plating the columns of the Philadelphia Public Buildings; Electro-deposition upon alu- minium .;........... 350 Advisability of previous coppering, and baths for that purpose; Prof. Nees' process 351 Electro-deposits produced by the Mannesmann Pipe Works, Germany . 352 CHAPTER XIV. GAI/VANOPI 42 Sn 12 " Na 4.6 Q Quantity of current. Ohm' s law. The quantity of electricity or, in other words, the current strength, which an element fur- nishes at a determined extreme point, depends on the strength of the electro-motive force which impels the current, as well as on the resistance which the conductor offers to the current. In the preceding it has been seen that the electro-motive force corresponds to the difference of the potentials of two conductors connected by a metallic wire ; the greater this difference is, the greater the energy with which the compensation of the elec- tricities takes place. It has also been explained that the re- 18 ELECTRO-DEPOSITION OF METALS. sistance increases in proportion to the length, and decreases with the increase in the cross-sectfon of the conductor. Upon these relations Ohm's law is based, and in its completeness it may be summed up as follows : The quantity of electricity or the strength (intensity} of current is directly proportional to the sum of the electro-motive forces of the exciting elements, and is in- versely proportional to the sum of the resistances of its closing circuit; however, the resistance of each part of the closing circuit is proportional to its length and inversely proportional to its cross- section. Now, if 5 indicates the strength of current, E the sum of the electro-motive forces, and L the total resistance, then the strength of current 5 is S-jj-, The total resistance L is, however, composed of two different resistances, namely, of the so-called essential or internal resist- ance, which expresses the resistance of the substances in the elements themselves, and of the non-essential or external resist- ance of the closing circuit. If, therefore, the internal resistance R and the external resistance = r, the total resistance will be L = R + r, and the formula given above is changed to R \-r Let us now examine the useful applications which result from Ohm's law, to the coupling of the elements, they being of great importance to the practical electro-plater. According to the above formula, which expresses the total performance of a bat- tery, the strength of current of a single element is, if s indicates its current strength, e the electro-motive force, R the essential or internal resistance, and r the resistance in the closing circuit, R+r By now uniting several such elements, let us say n elements, to a column, the electro-motive force of the latter has become n -f e = ne y and the internal resistance nr; with the same closing circuit as that of the single element, r will not increase, hence the strength of these n elements must be written MAGNETISM AND ELECTRICITY. 1 9 ~ n R + r It is now clear that when a determined closing circuit of the resistance r is given that the strength of current cannot -be in- definitely augmented by increasing the number of n elements ; because, though the electro-motive force, by the augmentation of n elements, increases by so many n, the internal resistance R also grows, so that finally the value r, which remains constant, disappears, contrary to the resistance R, which increases n times. Hence, the strength of current constantly approaches more the limit of value On the other hand, the effect can neither be increased by enlarging the area of the pair of plates nor by decreasing the resistance of the fluid in a given number of elements. Because when r, the external resistance, is sufficiently large so that the internal resistance, n R, may be neglected, the intensity always & approaches more the value . Hence, it follows that the augmentation of the area of the ex- citing pair of plates produces an increase in the current-strength only when the external resistance in the closing circuit is small in proportion to the internal resistance of the battery. If we now apply the results of the above explanations to practice, we find that the elements may be coupled in various ways according to requirement. i. If, for instance, four Bunsen elements (carbon-zinc) are coupled one after another in such a manner that the zinc of one element is connected with the carbon of the next, and so on (Fig. 2), the current passes four times in succession through an equally large layer of fluid, in consequence of which the in- ternal resistance, 4 R, is four times greater than that of a single element, while the resistance of the closing circuit, r, remains the same. Hence, while the current-strength is thereby not in- creased, the electro-motive force is, and for this reason this 20 ELECTRO-DEPOSITION OF METALS. mode of coupling is called the union or coupling of the elements for electro-motive force or tension. FIG. 2. 2. By connecting four elements alongside of each other, i. e., all the zinc plates and all the carbon plates one with another FIG. 3. FIG. 4. (Fig. 3), the current simultaneously passes through the same layer of fluid in four places ; the internal resistance of the bat- tery is therefore the same as that of a single element, and since the area of the plates is four times larger than that of a single element, the quantity of current is aug- mented by this mode of coupling. This is called coupling for quantity of current. 3. Two elements may, however, be connected for electro-motive force or tension, and several such groups coupled alongside of each other as shown in Fig. 4, whereby, according to what has above been said, the electro-motive force as well as the cur- augmented. This rent strength is mode of connection is called mixed coupling. According to the resistance of the bath, as well as of the ex- terior closing circuit, and the surfaces to be plated, the electro- MAGNETISM AND ELECTRICITY. 21 plater may couple his elements in either way, and in speaking later on of the elements the various modes of coupling will be further discussed. We will here only mention the proposi- tion deduced from Ohm's law that a number of galvanic elements yield the maximum of intensity of current when they are so arranged that the internal resistance of the battery is equal to the resistance in the closing circuit. Hence, when operating with baths of good conductivity and slight resistance, for instance, acid copper baths, silver cyanide baths, etc., with a slight dis- tance 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. The effects of the electric current are thermal, physiological, electro-magnetic, inductive, and chemical ; however, for our purposes, only the last three need be discussed. Electro-magnetism. If a wire conveying the electric current be brought near a magnetic needle, the latter will immediately be deflected from its direction, no matter whether the wire conveying the current be placed alongside, above, or beneath the magnetic needle. The direction which the needle will assume when placed in any particular position to the conducting wire, may be determined by the following rule: Let the current be supposed to pass through a watch from the face to the back : the motion of the north pole will be in the direction of the hands. Or, let the ob- server imagine himself swimming in the direction of the current with his face towards the needle : the north pole of the needle will then be deflected towards his left hand. When the needle is subjected to the action of two currents in opposite directions, the one above and the other below, they will obviously concur in their effects. The same thing happens 22 ELECTRO-DEPOSITION OF METALS. when the wire carrying the current is bent upon itself and the needle placed between the two portions ; and since every time the bending is repeated a fresh portion of the current is made to act in the same manner upon the needle, it is easy to see how a current, too feeble to produce any effect when a simple straight wire is employed, may be made by this contrivance to exhibit a powerful action on the magnet. It is on this principle that instruments called galvanoscopes, galvanometers, or mtdtipliers are constructed. They serve not only to indicate the existence of electrical currents, but also to show by the effects upon the needle the direction in which they are moving. The delicacy of the instrument has been increased 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 fibre of untwisted silk, with the lower needle in the coil and the upper one above it. The advantage thus gained is twofold : the sys- tem is astatic, unaffected, 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- MAGNETISM AND ELECTRICITY. 23 fleeting 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 more highly magnetic the greater the number of turns of the coil, and the more intense is the current passing through the turns. However, not only the iron bar, around which the current circulates, becomes magnetic, but also a conducting wire through which passes a strong current. By suspending a cir- cular conducting wire so that it is free to move around its ver- tical axis, its direction is affected by the magnetism of the earth, and it will take up a position so that its plane stands at a right angle to the plane of the magnetic meridian ; by now conducting the current through a wire having the form of a long helix, a so-called solenoid, the wire will, in a like manner, place itself with the turns of the helix at right angles to the plane of the magnetic meridian, or, in other words, the axis of the solenoid will lie in the magnetic meridian. In the same manner as an electrified conducting wire acts upon a magnet, two electrified wires exert an attracting and re- pelling influence on each other, the general law of the action being that electric currents moving in parallel lines attract one another if they move in the same direction, and repel one another if they move in opposite directions. Induction. By induction is understood the production of an electric cur- rent in a closed circuit which is in the immediate neighborhood of a current-carrying wire. Suppose we have two insulated copper wire spirals, A and B (Fig. 5), B being of 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. 2 4 ELECTRO-DEPOSITION OF METALS. This current is recorded by the deflection of the magnetic needle of a multiplier, M, which is connected with the ends of A, the deflection of the needle showing that the current pro- duced in A by the current in B moves in an opposite direction. The current in A, however, is not lasting, because, after a few oscillations, the magnetic needle of the multiplier returns to its previous position and remains there, no matter how long the current may pass through B. If, however, the current in B be interrupted, the magnetic needle swings to the opposite direc- tion, thus indicating the formation of a current in A, which passes through it in the same direction as the interrupted current in B. FIG. 5. The current causing this phenomenon is called the primary or inductive current, and that produced by it in the closed cir- cuit the secondary or induced current. From what has been above said, it is clear that an electric current at the moment of its formation induces in a neighboring 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 inductive MAGNETISM AND ELECTRICITY. 25 current, its sudden augmentation also effects the induction of a current of opposite direction in a neighboring wire, while its sudden weakening induces a current of the same direction ; the same effect being also produced by bringing the inductive wire closer to, or removing it further from, the neighboring wire. The induced currents being alternately formed by opening and closing the circuit, and they showing different directions, the term alternating currents has been applied to them. If the turns of the spirals are very close together, each turn induces the other, the so-called extra currents being thereby formed. The induced currents follow Ohm's law the same as the in- ductive current. A long inducing wire with a small cross-sec- tion offers greater resistance than a short wire with a larger cross-section, and consequently in the first case the current will possess slighter intensity and higher tenison, and in the other greater intensity and less tenison. In the same manner as an electrified wire induces a current in a neighboring wire, a magnet or electro-magnet also produces induced currents in a coil of wire surrounding it. These cur- rents act in the same manner as those produced by other means, and by taking into consideration Ohm's law, currents of great and slight intensity can be produced at will, as will be seen in speaking of the dynamo-electric machines, the construc- tion of which is based upon the principle of induction. Chemical actions of the electrical current Electrolysis. An electric current on being conducted through a fluid effects the reduction of its constituents. By cutting, for instance, the conductor of an electric current, and introducing the two wire ends thereby formed into water acidulated with dilute sulphuric acid, the water, provided the current is strong enough, is de- composed into its constituents, hydrogen and oxygen, the former separating in the form of gas on the negative pole and the latter on the positive. If such a decomposition does not take place, the fluid does not conduct the current. Pure water 26 ELECTRO- DEPOSITION OF METALS. by itself is a bad conductor, and to make its decomposition possible it has to be made conductive by acidulation with dilute sulphuric acid. When a chemical composition is decomposed by the current, the constituent forming the basis of the combi- nation separates on the negative pole, and that constituting the acid on the positive ; hence metals and hydrogen are liberated on the negative, and acids and oxygen on the positive pole. To Faraday is due the discovery of the chemical actions of the current and the exposition of the laws governing the separation of the constituents. He adopted the term electrolysis for the electrical separation of chemical combinations, and electrolyte ior the fluids subjected to electrical decomposition. To the poles or plates leading the current into and out of the electro- lyte he applied the term electrodes, the positive pole being the anode, and the negative pole the cathode. The elements of the electrolyzed liquid, which are liberated by the action of the current, are termed ions, those set free on the anode or positive electrode being termed anions, and those at the cathode or negative anode cations. Thus, when acidulated water is electro- lyzed, two ions are evolved, namely, oxygen and hydrogen, the former at the positive and the latter at the negative electrode. It is absolutely necessary for the electrolyte to be in a fluid state, though it does not matter whether the fluid state is pro- duced by solution or fusion. We know no more of the actual cause of the chemical action of electricity than of its nature and origin. According to Clausius' theory, matter is composed of minute particles called molecules, which, though mechanically indivisible, are chem- ically divisible. The constituent parts of the molecules which are no further chemically divisible are called atoms. Clausius supposes that the molecules are in constant motion ; that in solid bodies they move around determined positions of equi- librium, while in fluids even apparently tranquil they move from one place to another, constantly revolving and pushing against one another without being subjected to a return to their original positions. In pushing against one another the molecules are MAGNETISM AND ELECTRICITY. 27 decomposed into the atoms of which they are composed ; those atoms, however, which have become electro-negative under the influence of the current endeavor to reach the anode, while those which have become electro-positive move towards the cathode. But in doing this they meet atoms of opposite polarity, with which they reunite to a molecule until they are again liberated by this molecule pushing against another, when they move further towards the anode. Arriving at the electrodes, they find no more atoms of opposite polarity with which they might unite to a molecule ; both atoms, therefore, remain free on the electrodes, while the electrolyte between the two electrodes suffers no perceptible change. The atoms are, therefore, to be considered as ions. However, in order that the ions may be attracted by the electrodes, a current of determined electro- motive force is required ; as otherwise, though the electrolyte may conduct the current, the atoms attract one another more vigorously than they are attracted by the electrode, and again form molecules. To this mutual attraction of the atoms of oppo- site polarity is due the resistance of the electrolyte to the trans- mission of the current, and also the formation of a current of an opposite direction to that of the primary current, which is called the counter or polarizing current. This counter current, which is so effectually utilized with accumulators (secondary batteries), is the worst enemy of the electro-plater, and to overcome it very strong currents have frequently to be used, as will be shown, for instance, in nickeling sheet zinc. Faraday is also the discoverer of the following electrolytic laws : First law. The quantity of substance separated within a de- termined time by the current is directly proportional to the strength of the current. By conducting the current through a volt- meter (Fig. 6), i. e. t a closed decomposing cell provided with two platinum electrodes, which are in contact with the poles of the element, and dip into acidulated water, oxygen evolves on the positive electrode and hydrogen on the negative. The gas mixture (oxyhydrogen gas) is conducted through a bent tube 28 ELECTRO-DEPOSITION OF METALS. FIG. 6. inserted air-tight in the stopper of the cell, into graduated ."..; tubes, in such a manner that the gas enters the tubes under water. The escaping mixture of gas rises in the form of bubbles into the upper part of the tube, and the volume of gas there collected in a determined time can be readily read off. Now, if a current of determined strength has produced a determined quantity of oxyhydrogen gas in the voltmeter, a. current twice as strong will, according to Faraday's law, produce in the same time double the volume of gas, from which further results the fact that for the decomposition of a determined quantity of any body, a constant quantity of current is always re- quired, to which the term electrical eqivalent might be applied. Second law. If the same current acts upon a series of differ- ent solutions, the weights of the elements separated at the same time in each solution are proportional to their chemical equivalents. If, for instance, the same current be conducted through three decomposing cells, one of which contains water, the second a solution of blue vitriol, and the third a solution of nitrate of silver, for each gramme of hydrogen developed in the first cell, 31.75 grammes of copper will be separated in the second cell, and 1 08 grammes of silver in the third cell, because their chemical equivalents are as I : 31.75 : 108. Third law. In an element, the chemical decomposition the dissolution of zinc is proportional to the strength of current ; or, in other words, as many equivalents of zinc are dissolved in the element as equivalents of another metal are separated in an in- serted electrolyte. Every electro-plater observes that the zinc cylinders of the elements are dissolved ; and it is just this solu- MAGNETISM AND ELECTRICITY. 2Q tion which maintains the development of the electric current. As is well known, zinc is strongly attacked and dissolved by dilute sulphuric acid; therefore a dissolution of zinc takes place before the galvanic apparatus is closed. This dissolution of zinc, independent of the production of current, is termed local action, and to decrease it the zinc is amalgamated by first wash- ing it with strong soda to remove grease. Then it is dipped into a vessel of water containing T V of sulphuric acid. As soon as strong action takes place it is transferred to a suitable dish, mercury poured over it, and finally is rubbed till a bright silver-like film forms ; then it is set up on edge to drain, and before use any globules set free are rubbed off. If local action has thus been prevented, only as much zinc will dissolve, according to this law, as is chemically equivalent to the metal separated in the decomposing cell. If, however, local action is present, the consumption of zinc is increased by the quantity corresponding to solution by local action. Electro-chemical equivalents. This term is applied to the weights of the various electrolytes which are decomposed in the unit of time by the electric unit. The electro-chemical equivalents are proportional to their chemical equivalents. The electro-chemical equivalent of a body is found by multiplying its chemical equivalent by the electro-chemical equivalent of hydrogen=o.ooo 1 022 . When an electric current passes through a conductor, the latter becomes more or less heated. According to Joule's ex- periments, it was found that the development of heat in the con- ductor is proportional to its resistance; and further, that it is pro- portional to the square oj the strength of current. Hence the development of heat will be the greater the smaller the cross-section of the conductor and its conducting capacity are, and the larger the quantity of current which passes through it. For practical purposes, the conclusion derived from this is the necessity of choosing conducting wire of good conducting capacity and of sufficiently large diameter to prevent the devel- opment of heat, which in this case means loss of current. 30 ELECTRO-DEPOSITION OF METALS. Consumption of power in electrolysis. Without a desire fur- ther to enter into the details of the electro-chemical theory, it may for the sake of completeness, be mentioned that the force required for the decomposition of an electrolytic solution is at least equal to that which, when converted into heat, corresponds to the heat developed by the separated bodies in their reunion into their original combination. Electric units. The electro-motive force required for the de- composition being frequently given, as well as the intensity which the current must possess in order properly to coat a de- termined surface of article with the electrolytically separated metal, the electric units serving for electric measures will be briefly given : To measure the physical phenomena of the current it is nec- essary to refer to mass, length, and duration of time, and the units adopted by the International Congress of 1881 are as fol- lows : 1. Unit of length, I centimetre. 2. Unit of time, I second. 3. Unit of mass, the mass of one gramme. The term fundamental or C. G. S. (centimetre-gramme-sec- ond) units has been applied to this system. Force or power (F) Dyne. Force which acting upon I gramme for a second generates a velocity of I centimetre per second. Work Erg. Amount of work done by I dyne working through i centimetre of distance. Quantity. The quantity conveyed by unit current in i second. Potential or electro-motive force. The difference of the electric condition between two conductors or two points of a conductor, when the transference of electricity from one to the other is proceeding at the rate of i erg of work per unit of electricity transferred. Resistance. A resistance such that with unit of difference of potential between the ends of conductor, I unit of current is conveyed along it. MAGNETISM AND ELECTRICITY. 31 Of the so-called practical units, which were retained by the Congresses and Conferences of 1881 and 1884, there are five: the ohm, volt, ampere, farad, and coulomb. The ohm is the practical unit of resistance. It is equal to the resistance of a column of mercury I metre long and I square millimetre in cross-sectional area at o C., and approximately "equal to the resistance of 48.5 metres of pure copper wire, I millimetre in diameter, at OC. The ohm is equal to io 9 C. G. S. units. The ampere is the practical unit of the current-strength (in- tensity) ; it is equal to T ^ of the theoretical C. G. S. unit. For practical purposes the quantity of silver precipitated in one second is taken as the representative value of an ampere, 0.0011188 gramme of silver corresponding, according to Kohl- rausch, to one ampere. The volt is the practical unit of the electro-motive force, and is equal to io 8 C. G. S. units. It is approximately equal to the electro-motive force of a single Daniell's cell. 'The farad is the practical unit of capacity equal to io 9 C. G. S. units ; the coulomb is the unit of quantity, i. e., the volume of current equal to that of I ampere passing through a circuit for one second of time. A current of I ampere at the pressure of I volt is termed a watt; it is a most useful unit for comparing different currents, and is really the product of volume into pressure. The English horse-power (H. P.) is taken at 550 foot-pounds per second, and is thus equivalent to raising 550 pounds through one foot, or one pound through 550 feet, in a second. (The French H. P. is 542.48 foot-pounds per second.) Ill SOURCES OK CURRENT. CHAPTER III. GALVANIC ELEMENTS THERMO-PILES MAGNETO- AND DYNAMO-ELECTRIC MACHINES. THE sources of current used for electro-deposition of metals are the galvanic elements, thermo-piles, magneto-electric machines, and dynamo- electric machines. A. GALVANIC ELEMENTS. It is not proposed to enter into a detailed description of all the forms of galvanic elements, because the number of such constructions is very large, while the number of those which have been successfully and'permanently introduced for practical work is comparatively small. The original form of the galvanic elements, the voltaic pile, consisting of zinc and copper plates separated from one another by moist pieces of cloth, has been already 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 f 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 GALVANIC ELEMENTS. 33 one another in the same vessel, the copper plate of the one vessel being connected with the zinc plate of the next, and so on. In all elements with one fluid as an excitant, the current is quite strong at first, but quickly decreases for the following rea- sons : First, during the interruption of the current, a change takes place in the fluid by the local action in the element, and then with a closed circuit the zinc with the impurities it con- tains forms small voltaic piles, the element consequently also performing a certain chemical work during the interruption of the current. As mentioned on p. 29, the local action can be reduced to a minimum by amalgamating the zinc. Such amalgamation is also a protection against the above-mentioned chemical work of the element, the bubbles of hydrogen adher- ing so firmly to the amalgamated homogeneous surface as to form a layer of gas around the zinc surface, which prevents its contact with the fluid. Amalgamation may be effected in various ways. The zinc is either scoured with coarse sand moistened with dilute sulphuric or hydrochloric acid, or pickled in a vessel containing either of the dilute acids. The mercury may be either mixed with moist sand and a few drops of dilute sulphuric acid, and the zinc be amalgamated by applying the mixture by means of a wisp of straw or a piece of cloth ; or the mercury may be ap- plied by itself by means of a steel wire brush, the brush being dipped in the mercury, and what adheres quickly divided 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 a mercury salt and rub with a woollen rag. A suitable solution is prepared by dis- solving 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. In order to preserve as much as possible the coating of mercury upon the zinc, sulphuric 3 34 ELECTRO-DEPOSITION OF METALS. acid saturated with neutral mercuric sulphate is used for the ele- ments ; for which purpose frequently shake the concentrated sul- phuric acid (before diluting with water) with the mercury salt. Bouant recommends instead of the addition of mercuric sul- phate, 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 I quart of water, with an excess of a mix- ture of equal parts of mercuric sulphate and mercuric chloride, and, after cooling, filter and use the clear solution. The third reason for the decrease of the current-strength in elements with one fluid is polarization. By polarization is un- derstood the appearance in the element of a second current which, being opposite to that produced by the element, weak- ens the action of the latter. The cause of galvanic polarization is found in the fact that the negative pole-plate becomes coated with a layer of hydrogen, whereby according to Clausius's the- ory (p. 26) the attraction of the anodes for the ions is essenti- ally weakened, while, according to another theory, the electro- negative plate, by contact with the layer of gas, becomes elec- tro-positive towards the other, which is coated with bubbles of oxygen. Polarization can only be entirely avoided in elements the neg- ative pole-plate of which dips into a fluid which oxidizes the hydrogen to water, as is the case in the so-called constant ele- ments with two fluids, as will be seen later on. Proceeding from the conviction that rough surfaces allow the bubbles of hydrogen to pass off much more freely than smooth surfaces, Smee constructed the element named after him. It 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. The platin- izing is effected by hanging the silver plates in a vessel filled GALVANIC ELEMENTS. 35 with acidulated water, adding some chloride of platinum, and placing the vessel in a porous clay cell filled with acidulated water and containing a piece of zinc, the latter being connected with the silver plates by copper wire. The platinizing obtained in this manner is a black powder which roughens the surfaces, in consequence of which the bubbles of hydrogen become read- ily detached and the 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 element, it is advisable to add some chloride of platinum to the dilute acid of the element. The electro-motive force of the Smee element 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 oxidizes the hydrogen to water. From this conviction originated the so-called constant elements with two fluids, the first of these elements being, in 1829, constructed by Becquerel, which, in 1836, was succeeded by the far more effective one of Daniell. As most generally used, Daniell's element (Fig. 7) consists of a glass vessel, a copper cylinder, a porous clay cell, and a rod of zinc suspended in the latter. The glass vessel is filled with concentrated solution and a small piece of blue vitriol, and the porous clay cell with dilute sulphuric acid. The oxygen evolved on the electro-positive zinc oxidizes the latter, sulphate of zinc being formed, while the hydrogen sep- arating on the electro-negative copper reduces from the blue vitriol solution a quantity of copper equivalent to it, which sep- arates upon the electro-negative plate. However, after a com- paratively short time of working, the dilute sulphuric acid is FIG. 7. ELECTRO-DEPOSITION OF METALS. FIG. 8. consumed for the formation of sulphate of zinc, the electro- motive force becoming very weak. The necessity of frequently renewing the dilute sulphuric acid is an inconvenience whfch the Daniell elements show more than any others. Furthermore, by the action of osmose, blue vitriol solution gets into the por- ous cell, where it is decomposed by coming in contact with the zinc, the copper being separated upon the latter, whereby the effect is destroyed or at least very much weakened. The electro- motive force of the Daniell element is about I volt. The Meidinger element may be considered a modified Daniell element. Like the Callaud element, it has no porous division, the mixture of the two fluids being prevented by their different specific gravities. The shape of the Meidinger element, as most generally used, is shown in Fig. 8. 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 b, 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 en- tire element is also filled with Epsom salt solution (i 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 circuit is not closed, the concentrated copper solution re- mains quietly standing in K, its greater specific gravity pre- venting it from rising higher and reaching the zinc. If, how- ever, the circuit be closed, zinc is dissolved, while metallic copper is separated from the blue vitriol solution, and concen- trated solution flows from the balloon C to the same extent as GALVANIC ELEMENTS. 37 the blue vitriol solution in D becomes dilute by the separation of copper. Hence the action of the element remains constant for quite a long time, and of all the modified forms of Daniell's element consumes the least blue vitriol for a determined quantity of current. However, in consequence of its great in- ternal resistance (9.90 ohms) its current-strength is small. The electro-motive force of the Meidinger element is 0.95 volt. Grove, in 1839, substituted platinum for copper ; the platinum dips in concentrated nitric acid, while the zinc cylinder stands in dilute sulphuric acid. The hydrogen liberated on the platinum is oxidized to water by the nitric acid, hyponitrous acid escaping in the form of gas. The electro- motive force of the Grove element is at first double that of the Daniell element, but it soon abates on account of the dilution of the nitric acid by water. To prevent this weakening, concentrated sulphuric acid, which absorbs the water formed by the oxidation of the hydrogen, may be added to the nitric aeid. Though the resist- ance of the Grove element is small (0.70 to 0.75 ohm), and its electro-motive force 1.70 to I.QO volts, according to the con- centration of the solutions, it is but seldom used on account of its costliness. Bunsen, in 1841, replaced the expensive platinum 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 glowing it with the exclusion of air. After cooling, the carbon is again saturated with sugar solution (others use tar, or a mixture of tar and glycerine) and again glowed with the exclusion of air, these operations being, if necessary, repeated once more, es- pecially when great demands are made on the electro-motive force and solidity of the artificial carbons. Figs. 9, 10, and 1 1 show the three forms of Bunsen's elements most generally used. ELECTRO-DEPOSITION OF METALS. Fig. 9, which is the most convenient and practical form, con- sists of an outer vessel of glass. In this is placed a cylinder of zinc in which stands a porous clay cell, 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 its working, when the material is good, is exceedingly dim- cult. It is generally cut with a thin, strip of iron and watered silver-sand. Blocks for Bunsen cells cost less because they are more, easily produced. Rods for Bunsen cells should be a few inches longer than the pots to protect the top contact from 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 sol- dered or secured by means of a binding-screw to the zinc cyl- inder while the prism of gas-carbon carries the binding-screw (armature), as seen in Fig. 9, in the upper part of which acop- FIG. 9. FIG. 10. FIG. ii. per sheet or wire is fixed for the transmission of the current. The outer vessel is filled with dilute sulphuric acid ( I part by weight of sulphuric acid of 66 Be. free from arsenic and 1 5 parts by weight of water), and the porous cell 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. 10 the cylinder of artificial carbon is in the glass ves- GALVANIC ELEMENTS. sel, while the zinc, which, in order to increase its surface,. has a star-like cross-section, is placed in the porous clay cell. 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 element shown in Fig. 9 is more advantageous, because its effective zinc surface can be kept larger. Fig. 1 1 shows a plate element such as is chiefly used for bichromate batteries. FIG. 12. Fig. 12 shows an improved Bunsen cell of great power for nickel and electro-plating, electro-motors, etc. It has an electric- motive force of 1.8 volts. When the absence of power prevents the use of a dynamo, a battery of these cells is very suitable for nickel-plating. It is an easy battery to set up and keep in working order. The batteries are set up by well amalgamating, inside and outside the zinc, and placing it in the jar. Inside the zinc place the porous cup, and within the porous cup the carbon, and then pour nitric acid in the porous cup. In the outer jar pour a mixture of I part sulphuric acid to 12 of water (previously mixed and allowed to cool). This acid mixture should cover the zinc or be on a level with the liquid in the porous cup. When the liquid in the outer jar becomes milky, 40 ELECTRO-DEPOSITION OF METALS. withdraw it with a syringe or siphon, and refill, adding occa- sionally small quantities of nitric acid to the porous cup, and keeping the zinc thoroughly amalgamated by one of the methods given on page 33. A very good plan of amalgamating zinc is as follows : Dip in lye to remove grease, rinse, then dip in the dilute acid in the glass jar, and then brush over with about 2 ozs. of mercury contained in a little flannel bag. Electro poion may be substituted for the nitric acid in the por- ous cup. This battery liquid consists of I Ib. of bichromate of potash dissolved in 10 Ibs. of water, to which 2^/ 2 Ibs. of com- mercial sulphuric acid have been gradually added. The Bunsen elements are much used for electro-deposition, since they possess a high electro- motive force (1.88 volts) and, on account of slight resistance (0.25 ohm), develop consider- able current- strength. Like the Grove elements, they have the inconvenience of evolving vapors of hyponitrous acid, which are not only injurious to health, but also attack the metallic articles in the workshop. Wherever possible they should be placed in a box at such a height that they may be readily manipulated. This box should have means of ventilation in such a way that the air coming in at the lower part will escape at the top through a flue, and carry away with it the acid fumes disengaged. It is still better to keep the elements in a room separate from that where the baths and metals are to be ope- rated upon. Furthermore, as the nitric acid becomes diluted by the oxidation of the hydrogen, and the sulphuric acid is con- sumed in the formation of sulphate of zinc, the acids have to be frequently renewed. To avoid the acid vapors, as well as to render the elements more constant, A. Dupre has proposed the use of a 30 per cent, solution of bisulphate of potash in water in place of the dilute sulphuric acid, and a mixture of water 600 parts, concentrated sulphuric acid 400, sodium nitrate 500, and bichromate of potash 6c, 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- GALVANIC ELEMENTS. 4! rately concentrated (about 30 per cent.) solution of bisulphate of potash or soda, and the clay cell with solution of chromic acid I part chromic acid to 5 parts water. As soon as the electro-motive force of the element abates, it is strengthened by the addition of a few spoonfuls of pulverized chromic acid to the chromic acid solution. It is better to use the chromic acid in the form of powder, which is especially prepared for this purpose, than a chromic acid solution produced by mixing solu- tion of bichromate of potash with sulphuric acid, the tendency of such a solution to form crystals exerting a disturbing effect. The chromic acid solution loses effect in a comparatively short time, the electro-motive force decreasing in a few hours, and chromic acid must be added, or the cell refilled. Another soluble chromium combination which depolarizes with rapidity and maintains the constancy of the elements for a much longer time, is obtained by treating pulverized chrome- ironstone with concentrated sulphuric acid and careful dilution with water. With a single filling of this solution the battery could be kept working for six days from morning to evening without refilling being required. During the night the battery remained filled, but inactive. The electro-motive force of an element filled with the chromium solution is to be sure some- what less than when nitric or chromic acid is used, it amount- ing to 1.5 volts, but on account of the great constancy and consequent cheapness of the filling, the fact that an additional element has to be added for a bath requiring a greater tension than 3 volts for decomposition need not be taken into con- sideration. In using nitric acid it is also advantageous to pour a 0.39 to 0.78 inch thick layer of oil upon the acid, to decrease the vapors. The binding screws which effect the metallic contacts must of course be frequently inspected and cleaned, which is best done by means of a file or emery paper. It is advisable to place a piece of sheet platinum between the binding surface of the carbon armature and the carbon in order to prevent the -42 ELECTRO-DEPOSITION OF METALS. acid rising through the capillarity of the carbon from acting directly upon the armature (generally brass or copper). To prevent the acid from rising, the upper portions of the carbons may be impregnated with paraffine. For this purpose the car- bons are placed f to I 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 paraffine is removed by scraping with a knife-blade or rasp. Manipulation of Bunsen elements. Before using the elements the zinc cylinders should be very carefully amalgamated accord- ing to one of the methods given on p. 33. The nitric acid need not be pure, the crude commercial acid sufficing, but it should be as concentrated as possible and show at least 36 Be. For the prisms it is best to take carbon produced in gas-houses using coal without the addition of brown coal, the electro- motive force of the latter being less. If artificial carbon is em- ployed, it 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 elements. In order to avoid an unnecessary consumption of zinc and acid, the elements are taken apart when not in use, for instance, over night. Detach the brass armature of the carbon prism and lay it in water to which some chalk has been added ; lift the carbon from the clay cylinder and place it in a porcelain dish or earthenware pot ; empty the nitric acid of the clay cell into a bottle provided with a glass stopper; place the clay cell in a vessel of water, and finally take the zinc cylinder from the dilute sulphuric acid and place it upon two sticks of wood laid across the glass vessel to drain off. In putting the elements together the reverse order is fol- lowed, the zinc being first placed in the glass vessel and then the carbon in the porous clay cell. The latter is then filled about three-quarters full with used nitric acid, and fresh acid is added until the fluid in the clay vessel stands at a level with that in the outer vessel. The cleansed brass armature is then screwed upon the carbon prism. Finally, add to the dilute GALVANIC ELEMENTS. 43 FIG. 13. sulphuric acid in the outer vessel a small quantity of concen- trated sulphuric acid saturated with mercury salt. It is advisable to have at least a duplicate set of porous clay cells, and in putting the elements together to use only cells which have been thoroughly soaked in water. The reason for this is as follows : The nitric acid fills the pores of the cell, 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 cells 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 cell should not be at a higher level than the sulphuric acid, in the outer .vessel. When the Bunsen elements are'in steady use from morning till night, the acids will have to be entirely renewed every third or iourth day. The solution of sul- phate of zinc in the outer vessel is thrown away, while the acid of the clay cells may be mixed with an equal volume of concentrated sul- phuric acid, and this mixture can be used as a preliminary pickle for brass and other copper alloys. Foote s pinnacle gravity battery. Gravity batteries are especially suited for continuous work at a low rate, the operating cost being as low as, if not lower than, any other type of battery. Four of these cells in series will charge a small storage battery. The type of gravity shown in Fig. 13 is one of the best in the market. The battery is set up by placing the copper cross and zinc in position. Pour clean water into the jar until within two inches of the top, then drop in blue vitriol (sulphate of copper) 44 ELECTRO- DEPOSITION OF METALS. in small lumps. The battery may be made immediately avail- able by adding 4 ozs. of pulverized sulphate of zinc. When the hydrometer reads less than 15 Be., there is not enough zinc sulphate in solution ; when over 30 Be., there is too much. Oppermann s element is in the main a Bunsen element, but is distinguished from the latter by nitric acid containing molybdic acid being used as depolarizing fluid instead of pure nitric acid. It is also provided with a hollow porcelain body upon the clay FIG. 14. cell. This porcelain body is filled with a solution of potassium permanganate, whereby the escaping vapors are mostly ren- dered innocuous. Furthermore, the element when at rest con- sumes no material. To avoid the inconvenience of emptying the elements, Oppermann has provided his battery jars, close above the bottoms, with two tubulures opposite to one another. This arrangement allows of all the jars of a battery being con- nected with one another, as shown in Fig. 14. The first jar of the battery is connected by means of a rubber tube of suitable GALVANIC ELEMENTS. 45 length with a large tubulated supply-jar, while one of the tubulures of the last jar is provided with a massive rubber stopper. The supply-jar contains the exciting fluid for the ex- terior cells. The clay cell of the Oppermann element is closed by a hollow porcelain lid. The latter contains a fluid capable of absorbing or decomposing the vapors evolved by the decompo- sition of the depolarizing fluid containing nitric acid. In the centre of the porcelain lid is a square hole in which the carbon prism is secured. The fluid in the lid consists of a solution of potassium permanganate acidulated with a small quantity of sulphuric acid. The solution is prepared as follows : Dissolve I part by weight of pure potassium permanganate in 20 parts by weight of distilled water, and add to the solution about I part by weight of dilute sulphuric acid. The vapors of hypo- nitrous acid are absorbed with avidity by this solution, and oxidized partly to nitrous acid and partly to nitric acid. Both of these acids combine with the potassium or the manganous oxide, and the potassium permanganate solution, which exhibits at first a deep violet color, is finally completely decolorized. When this is the case, which will be in about 3 or 4 hours, the solution has to be renewed. This is done in the simplest manner by introducing about 5 ccm. of the solution into the lid by means of a pipette, whereby the solution consumed is forced from the lid, passes into the clay cell and enriches the depolar- izing fluid by the addition of fresh nitric or nitrous acid. The arrangement of the elements and their combination to a battery is effected as follows : The battery jars are placed as indicated in the illustration and connected with one another by means of rubber stoppers, glass tubes bent at a right angle and short pieces of rubber hose. It is advisable first to dip the rubber stoppers in water, then to press them firmly into the tubulures and finally to insert the glass tubes also previously moistened with water. For the sake of security the rubber stoppers are fastened to the tubulus with cord or wire. One tubulus each of the two end jars, however, remains free. The 46 ELECTRO-DEPOSITION OF METALS. free tubulus of the last jar is tightly closed with a massive rubber stopper, while that of the first jar is provided with a per- forated stopper and a glass tube, and is connected with the supply-jar by means of a rubber hose of suitable length. In the battery-jars thus connected the zinc cylinders are first placed, and next in the latter the clay cells, and finally in the clay cells the carbon prisms. The clay cells are then filled with the depolarizing fluid. The porcelain lids are next placed upon the carbon prisms and the brass binding-screws secured to the prisms. The size of the porcelain lids must be such that they reach into the clay cells and are about even with the upper edge of the latter. The holes on the upper side of the porce- lain lids remain open. For filling the lids with potassium per- manganate solution a pipette is used. At 5 ccm. the pipette is provided with a mark and it is filled up to that point by dipping it in the fluid or by suction. The upper opening is then closed with the index finger of the right hand and the point of the pipette introduced into the hole of the lid. By now removing the finger the contents of the pipette run into the lid. For filling the outer cells it is best to use a concentrated solu- tion of common salt, which is prepared by dissolving 35 parts by weight of common salt in 100 parts by weight of water. Should the solution be very turbid, it has to be filtered. This is also necessary in case the solution, while in use, deposits a muddy sediment. In place of common salt solution, a concen- trated sal ammoniac solution may be used. It is prepared by dissolving 25 parts by weight of sal ammoniac in 75 parts by weight of water. Dilute sulphuric acid (i part by weight of pure sulphuric acid in 30 parts by weight of water), with an addition of a small quantity of neutral sulphate of mercury, is also suitable as an exciting fluid. Common salt solution, how- ever, deserves preference ; and its action can be strengthened by the addition of a very small quantity of dilute sulphuric acid. The exciting fluid is brought into the supply-jar. The ordinary element is 7.87 inches in height and, when this size is used, the supply-jar must have a capacity of at least as many quarts GALVANIC ELEMENTS. 47 as there are elements in the battery. To fill the jars the supply-jar is placed at a higher level and the cock opened. The solution then runs into all the battery-jars connected with one another. After connecting the copper band of the zinc cylinder with the binding-screw of the carbon of the next ele- ment, the battery is ready for use. To connect the end poles of the battery with the respective apparatus, quite stout copper wire thoroughly insulated should be used. The wire should be at 0.079 inch in diameter, and be as short as possible. When work with the battery is to be interrupted, the supply- jar is placed at a lower level and the cock opened. The ex- citing fluid then escapes from the outer cells of the elements and the development of current ceases. While the battery is not in use, a small portion of the depolarizing fluid oozes through the clay cells and collects upon the bottom of the bat- tery-jars. This fluid must be removed before the battery is again put in operation. For this purpose the glass tubes bent at a right angle inserted in the tubulures of the jars are turned so that one leg points upwards. The rubber hoses are then withdrawn, the bent glass tubes turned downward and the jars emptied by tilting them. For filling the clay cells with fresh depolarizing fluid, a glass funnel with glass cock and long discharge tube is used, whereby it is, however, necessary to slightly lift the porcelain lid in order to reach the interior of the clay cell. The clay cells require emptying entirely only when the battery is not to be used for some time or when it is to be cleaned, which has to be done once in a while. When the exciting fluid in the outer cells has become ineffective, it has to be replaced by a fresh supply. How often the battery has to be cleansed and how often the exciting fluid has to be renewed, depends of course on the length of time the battery is in use. The efficacy of the battery can be still further increased by keeping the exciting fluid in the exterior cells in constant circulation, which is effected by the following arrangement: Each of the two end cells of the battery is connected with a 48 ELECTRO-DEPOSITION OF METALS. supply-jar of suitable capacity and the full jar of the two supply-jars is placed at a higher, and the empty jar at a lower, level. By means of a screw-clip the discharge and influx of the fluid are so regulated that the latter always stands at the same level. When the upper jar is empty, the position of the jars is reversed. By now placing the two supply-jars in a tub containing ice and thus constantly cooling the circulating ex- citing fluid, the heating of the elements which otherwise con- stantly takes place is avoided, and the battery can be kept working for a longer time without interruption. The ordinary Oppermann element, 7.87 inches high, has a tension of 1.85 to nearly 2 volts. The current strength meas- ured on the open element by means of the spiral ammeter is 15 to 20 amperes. The quantity of oxyhydrogen gas evolved, measured by the voltmeter, amounts to about 20 ccm. per minute. Thus far we have followed the statements of the inventor himself. The element has not yet been thoroughly tested in practice, and while it must be admitted that nitric acid con- taining molybdic acid exerts greater depolarizing action than either nitric or chromic acid by itself, it would seem to us that cleansing the glass-jars of the depolarizing fluid oozing through is nearly as laborious, and consumes as much time, as empty- ing the ordinary Bunsen elements. The Leclanche element (zinc and carbon in sal ammoniac solution with manganese peroxide as a depolarizer) need not be further described, it not being adapted for regular use in electro-plating. It is in very general use for electric bells, its great recommendation being that, when once charged, it retains its power without attention for several years. Lallande and Chaperon have introduced a copper oxide element, shown in Fig. 15, which possesses several advan- tages. It consists of the outer vessel G, of cast-iron or cop- per, 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 ebonite GALVANIC ELEMENTS. 49 cover carrying a terminal connected with the zinc. The her- metical 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 copper oxide, O, and the vessel is filled with a solution of 50 parts of caustic potash in 100 of water. When the circuit is closed, decomposition of water takes place, the oxygen which appears on the zinc forming with the latter zinc oxide, which readily dissolves in the caustic potash solution, while the FIG. 15. hydrogen is oxidized with the simultaneous reduction of copper oxide to copper. When the element is open, i. e. y the circuit not closed, neither the zinc nor the copper oxide is attacked, and hence no local action nor any consumption of material takes place. The electro-motive force of this element is 0.98 volt, and its internal resistance very low. It is remakably con- stant, and is well adapted for electro-plating purposes by using two of them for one Bunsen element. 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 4 50 ELECTRO-DEPOSITION OF METALS. acid from the air, whereby carbonate of potash would be formed, which would weaken the exciting action of the solu- tion. Fnrther, the vessel G forming the one pole must be in- sulated from the other as well as from the ground, as otherwise a loss of current or defective working would be the conse- quence. The regeneration of the cuprous oxide or metallic copper formed by reduction from the cupric oxide to cuprous oxide, re- quires it to be subjected to calcination in a special furnace. The expense connected with this operation is, however, about the same as that of procuring a fresh supply of cupric oxide. Lallande himself, as well as Edison, endeavored to bring the pulverulent cupric oxide into compact plates, but the regenera- tion of these plates was still more troublesome. By treatment with various chemical agents, Dr. Bottcher, of Leipsic, has suc- ceeded in producing porous plates of cupric oxide which, after subsequent reduction by absorption of oxygen from the air, can be readily re-oxidized to cupric oxide, but as far as we know, elements with these plates have not yet been intro- duced into commerce. Umbreit & Matthes bring into commerce an element known as cupron element, which is an improved Lallande element, and in which the cupric oxide is also brought into the form of plates. A square glass vessel or vat with a ground edge and closed with a hard rubber lid contains two zinc plates, and between the latter the porous cupric oxide plate. The glass vessel is filled with lye containing 20 per cent, of caustic soda, and the current is delivered through two clamps on the outside of the lid. According to Umbreit and Matthes' statements the reduced positive pole plates are regenerated, that is, re-oxidized to cuprous oxide by rinsing in water and allowing them to remain in a warm place for 20 to 24 hours, so that it is only necessary to replace the soda lye saturated with zinc oxide. The electro-motive force of the element is 0.8 volt; the normal current-strength, according to the size of the elements I, 2, 4 and 8 amperes. Like the Lallande element, this element works without odor. GALVANIC ELEMENTS. 51 The elements of Marie, Davy, Niaudet, Duchemin, Sturgeon, Trouville, and others being of little practical value, may be passed over. Duns 's potash element. On account of its great electro- motive force (1.6 volts) and slight internal resistance, this ele- ment would be well adapted for electro-plating purposes, if depolarization were effected more rapidly than is actually the case. Its construction is as follows : In a glass vessel stands a carbon cylinder closed below, and in the centre of the carbon cylinder a clay cell. The space between the clay cell and the interior wall of the carbon cylinder is filled five-sixths full with pieces of carbon. In the clay cell stands an amalgamated strip of zinc or zinc cylinder to which the conducting wires are soldered, the place of soldering, as well as the wire as far as it comes in contact with the fluid, being covered with gutta- percha. The edge of the carbon cylinder is coated with paraffine and carries the pole binding-screw. The filling of the element is effected by laying potassium permanganate in crystals upon the layer of carbon between the clay and carbon cylinders, and pouring a solution of I part of pure caustic potash in 2 of water into the clay cell, the pouring being con- tinued until the fluid runs over the clay cell upon the potassium permanganate and the layer of carbon, and finally fills the outer vessel up to about the breadth of two fingers from the edge. The action of the element is as follows : When the element is closed decomposition of water takes place, the oxygen com- bining with the zinc to form zinc oxide, which is dissolved by the potash lye, while the hydrogen is oxidized on the positive pole by the potassium permanganate. The latter, to be sure, contains much oxygen, and acts very energetically, but as it diffuses very slowly, depolarization, i. e., the removal of the hydrogen, is not so quickly effected as, for instance, in the Bunsen element, where the nitric acid rapidly diffuses. Hence with a slight external resistance, for instance, baths where the element has to furnish large quantities of current, the electro- motive force sinks very rapidly and with it the current strength, ELECTRO-DEPOSITION OF METALS. FIG. 1 6. and, therefore, the element is only suitable for electro-plating purposes when a current need only for a short time be pro- duced, but not for permanent work. In the first case it offers the advantage of being always ready for use, evolving no vapors, and when not in use consuming no material. It is prudent to protect this element from the action of the carbonic acid of the air by a close cover. The element shown in Fig. 16 has been patented in Germany, and is de- scribed by Knaffe and Kiefer,* of Vienna, as follows : The element consists of a combination of zinc and carbon. The zinc plate is g\ inches long, 4f inches wide, and of the thickness of pasteboard. It is amalgamated according to a new process. It is placed between two car- bon plates of equal size, the surface of which is twice that of the zinc. The carbon plates are connected with the con- ducting wires in such a manner as to pre- vent oxidation of the binding-screws and to secure constant contact. The zinc plate is suspended in a neutral salt solu- tion in a clay cell, the space between the latter and the carbon plates being filled with pieces of carbon. The consumption of zinc is very small. The principal advantage of this new ele- ment is, however, the depolarizing fluid of peculiar composition and powerful effect. The element has an electro-motive force of 1.9 volts, an in- ternal resistance of 0.17 ohm, and a constancy such as seldom is attained with primary elements, I volt ampere lasting for 100 hours. * Neueste Erfindungen und Erfahrungen, vol. xviii, p. 308. GALVANIC ELEMENTS. 53 We will add a few words in regard to plunge or bichromate batteries. They consist of a number of separate voltaic cells connected so as to form a single cell or electric source, and the plates of which are so supported as to be capable of being simultaneously placed in or removed from the exciting fluid. For our purposes it will suffice to mention the Bunsen plunge battery, shown in Fig. 17. For constructive reasons only one fluid is used, into which the zinc as well as the carbon plates FIG. 17. dip, a solution of chromic acid prepared by dissolving 10 parts of bichromate of potash and \ part of mercuric sulphate in 100 parts of water, and adding 18 parts of pure concentrated sul- phuric acid, being employed. More advantageous is a solu- tion of chromic acid in the form of powder in water, in the pro- portion of i 15, for the same reason as given on p. 41. Fig. 1 8 shows a bichromate battery as constructed by Fein. Into the 6 element-vessels standing in two rows in the wooden 54 ELECTRO-DEPOSITION OF METALS. box M dip the zinc and carbon plates, which are secured to wooden cross-pieces provided with handles, and may be main- tained at any desired height by the notch e in the standard G. According to the current-strength required, the plates are allowed to dip in more or less deeply. FIG. 1 8. Fig. 19 shows a bichromate battery as constructed by Keiser & Schmidt. In using the above-mentioned chromic acid solution, which has been recommended by Bunsen, the elements at first develop a very strong current, which, however, in a comparatively short time becomes weaker and weaker. The current-strength can be increased by adding at intervals a few spoonfuls of pulverized chromic acid to the chromic acid solution, which, however, finally remains without effect, when the battery has to be freshly filled. Hence, these batteries are not suitable for electro- plating operations requiring a constant current for some time. GALVANIC ELEMENTS. 55 For temporary use, for instance, by gold-workers and others, for gilding or silvering small articles, the bottle-form of the bichromate element (Fig. 20) may be advantageously em FIG. 19. FIG. 20. ployed. In the bottle A two long strips of carbon]united above by a metallic connection are fastened parallel to one another to a vulcanite stopper, and are there connected with the binding- screw ; these form the negative element, and pass to the bottom of the bottle. Between them is a short thick strip of zinc at- tached to a brass rod passing stiffly through the centre 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 its services are no longer required. This bichromate element is excellent for purposes requiring strong currents, where long action is not necessary. As this element readily polarizes, it cannot be advantageously employed continuously for any considerable period of time. It becomes depolarized, however, when left for some time on open circuit. The element gives an electro-motive force of about 1 .9 volts. ELECTRO-DEPOSITION OF METALS. In Stoehrer's battery (Fig. 21) two acids, dilute sulphuric acid and concentrated nitric acid, are used. The porous clay cell is omitted, the massive carbon cylinders K, K, etc., being 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. 21. FIG. 22. Fig. 22 shows a plunge battery manufactured by Dr. G. Lang- bein & Co., at Leipzig-Sellerhausen, Germany, the details of which will readily be understood without further description. The zinc plates dip into the diaphragms which are filled with a mixture of 26 Ibs. of water and 2 Ibs. of sulphuric acid free from arsenic in which 2f ozs. of amalgamating salt have pre- viously been dissolved. The carbon plates dip into the glass GALVANIC ELEMENTS. 57 vessels, which contain a solution of commercial crystallized chromic acid in water in the proportion of I part acid to 9 water. In place of this pure chromic acid solution the follow- ing mixture may also be used : Water 10 parts by weight, sodium dichromate 0.75 part by weight, pure sulphuric acid of 66 Be. 1.5 parts by weight. This solution shows no inclination towards crystallization. In the illustration only two elements are combined to a battery, but in the same manner a plunge battery of four and eight ele- ments may be constructed, the separate elements of which may all be coupled parallel, as well as one after the other, and in mixed groups. B. THERMO-ELECTRIC PILES. Though thermo-electric piles are only used in isolated cases for electro plating operations, for the sake of completeness their nature and best-known forms will be briefly mentioned. In the year 1822, Professor Seebeck, of Berlin, discovered a new source of electricity, namely, inequality of temperature and conducting power in different metals, or in the same metal in different states of compression FlG> 23> and density. When two pieces of different metals, connected together at each end, have one of their joints more heated than the other, an electric current is immediately set up. Of all the metals tried, bismuth and antimony form the most powerful combination. In Fig. 23 Bm represents a bar of bismuth, and mS a bar of antimony soldered to the bis- muth bar. By leading wires from B and 5 to a galvanoscope, G, and heating the point of junction m, the needle of the galvanoscope is deflected. From this it may be concluded that an electric cur- rent circulates in the closed circuit GB mS G. By a closer examination the direction of the current may be recognized, it flowing on the heated point of junction from the bismuth to the ELECTRO-DEPOSITION OF METALS. antimony, and in the connecting wire of the ends of the rods which remain cold, from the antimony to the bismuth. The current is the stronger the greater the difference in the tem- perature of the point of junction and the free ends of the bars. Hence the electric current will be especially strong when the place of junction is heated and the ends B and 5" are at the same time cooled off. A combination as above described is called a thermo-electric couple, and the electricity obtained in this manner thermo-electricity. By a suitable combination of several or many of such couples, a thermo-electric pile is ob- tained. Noe's thermo-electric pile (Fig. 24) consists of a series of FIG. 24. small cylinders, composed of an alloy of 36^2 parts of zinc and 62 y 2 parts of antimony for the positive element, and stout German silver as the negative element. The junctions of the elements are heated by, small gas-jets, and the alternate junc- tions 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. 25) consists of an alloy of 2 parts antimony and I of zinc for the negative metal, while GALVANIC ELEMENTS. 59 for the positive element ordinary tinned sheet-iron is employed, the current flowing through the hot junction from the iron to the alloy. To insure a good contact between the two metals a strip of tin-plate is bent into a narrow loop at one end. This portion is then placed in a mould and the melted alloy poured around it, so that it is actually imbedded in the casting. The pile shown in the illustration consists of five series, one placed above the other. Each series has ten elements grouped in a circle, and is insulated from the succeeding series by a layer of FIG. 25. cement, composed of powdered asbestos moistened with a solu- tion of potassium silicate. With the consumption of about 6^ cubic feet of gas per hour, such a pile precipitates 0.7 oz. of copper, which corresponds to an electro-motive force of about 17 amperes. Hauck ' s thermo-electric pile. An essential defect of Clamond's thermo-electric pile consists in that the junctions of the dissimilar metals are subjected to ready destruction by being exposed to the direct action of the flame. Further, it is very difficult, or at least inconvenient, to make repairs, since in such a case it may become necessary to take the entire pile apart. Hauck 6o ELECTRO- DEPOSITION OF METALS. has successfully overcome these defects by adopting the princi- ple of indirect heating, as well as by giving the couples a more suitable form and by improving the alloy. The couples form four-sided wedges, to which are attached cast-iron pieces that transfer the heat of the gas-burner to the couples. The electro- motive force of a single couple is ^ that of a Daniell element. Fig. 26 shows a combination of two piles standing upon a com- FIG. 26. mon plate, one of the piles being given in cross-section. The glass-vessel H, with the tube, B, G, R, I, serves as a regulator for the gas-pressure. The pile shown in the illustration serves for the production of metallic deposits on a small scale, especi- ally for analytical examinations. Hauck, however, also furnishes combinations of three larger piles. Gulcher s thermo-electric pile, invented in 1890, is shown in Fig. 27. It is arranged for gas-heating, and with a constant supply of gas requires a pressure-regulator. The negative GALVANIC ELEMENTS. 6l 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 tubes with the gas conduit, the latter being connected by means of a rubber tube with the pipe supplying the gas. Thus the gas first passes into the conduits, next into the nickel tubes, and leaves the latter through six small holes in a soap-stone 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 FIG. 27. a circular brass plate placed directly over the soap-stone socket. One end of it is soldered to the nickel tube, while the other ends, towards the top, in a socket in which are cast the positive electrodes. The latter have the form of cylindrical rods with lateral angular prolongations. To the ends of these prolonga- tions are soldered long copper strips secured in notches in the slate plate. They serve partially for cooling off and partially for connecting the couples. For the latter purpose each copper 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- 62 ELECTRO- DEPOSITION OF METALS. 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 i-Tfr-i- 5 200 = - 2 9 heat-unit. These correspond to 1208 volt-amperes, I volt-ampere being equal to 0.00024 heat-unit. Hence, in Giilcher's thermo-electric pile, which at present pro- duces the greatest useful effect, not much more than I per cent. of the 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 galvanic batteries, they hav- ing 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 com- paratively large, it being ten to twenty times that of Bunsen elements. Thus, for instance, Gulcher's thermo-electric pile costs $37.50 in Germany, to which have to be added $5 for the gas-pressure regulator, if required. C. MAGNETO- AND DYNAMO- ELECTRIC MACHINES. It is a well-known fact that all the early experiments and im- provements in dynamos were made with a view of perfecting an electrical machine for plating, and that the success attained therein was the forerunner of all the magnificent dynamo machines for other purposes in such general use. The principle of induction upon which the dynamo-electric machines are based has been explained on p. 23. Faraday, in 1831, made the important discovery that by moving a coil of GALVANIC ELEMENTS. 63 wire in the presence of a magnet a current of electricity was generated in the coil, or, vice versa, by moving the magnet and holding the coil stationary a like result was obtained. Thus a current of electricity was produced either "by moving a wire in the presence of a stationary magnet, or by moving a magnet in the presence of a stationary wire. The intensity of the current thus obtained depends on the power of the magnet and on the velocity with which the mag- net or coil is moved through the magnetic field. Upon these simple facts is based the whole of the recent important develop- ments of electrical science. Before describing the various attempts made to devise some mechanical means whereby the different elements which pro- duced the temporary or momentary currents could be com- bined, so as to collect them, and cause them to flow in rapid succession, the one after the other, without interruption, it will be well to remember that the necessary elements for producing these induced electric currents are simply a bar magnet and an insulated coil of wire. It will also be well to remember that every magnet, no matter what its form, has two poles a north and a south pole and each of these poles exerts a certain influence in its immediate neighborhood, the space thus affected being termed the magnetic field or the region of the lines of force. The attraction or magnetic force of these lines varies as the in- verse ratio of the square of the distance ; therefore, the nearer the magnet the greater the intensity of the magnetism. Fara- day proved that these lines, which he designated lines of force, showed by their position the direction of the magnetic force, and by their number its intensity. By passing a coil of wire through this field, so as to cause it to cut, as it were, a number of these lines of force, a current of electricity will be generated in the coil; and if it can be so arranged that a number of these coils will pass in rapid succession through the magnetic field, we shall have a series of impulses giving us practically a con- tinuous stream of electricity. Thus a magneto-electric or dynamo-electric machine is 64 ELECTRO-DEPOSITION OF METALS. simply a machine for the conversion of mechanical energy into electrical energy by means of magneto-electric induction. The term dynamo-electric machine is also applied to a machine by means of which electrical energy is converted into mechanical energy by means of magneto-electric induction. Machines of the latter class are generally called motors, those of the former generators. Prof. S. P. Thompson defines a dynamo-electric machine as follows : " A machine for converting energy in the form of mechanical power into energy in the form of electric currents, or, vice versa, by the operation of setting conductors (usually in the form of coils of copper wire) to rotate in a magnetic field, or by vary- ing a magnetic field in the presence of conductors." The term dynamo was first applied to such machines because of the form in which this machine first appeared, viz., the series- wound machine. It was self-acting, or required no excitement other than what it received by the rotation of its armature in the field of its magnets, or, indeed, in the field of the earth. A dynamo-generator, or a dynamo-electric machine proper, consists of the following parts: 1. The revolving portion, usually the armature, in which the electro-motive force is developed which produces the current. 2. The field magnets, which produce the field in which the armature revolves. 3. ^hs. pole piece S) or free terminals of the field magnets. 4. The commutator, by which the currents developed in the armature are caused to flow in one and the same direction. In alternating machines and in some continuous current dynamos this part is called the collector, and does not rectify the currents. 5. The collecting brushes, that rest on the commutator cylinder, and take off the current generated in the armature. The number of such dynamo machines is legion. In each case the arrangement of the armature of the magnets and of the commutators is varied, but the principle is always the same coils of insulated wire being caused to cut through magnetic fields, as already explained. GALVANIC ELEMENTS. 65 The first attempt to devise an electrical machine was made by Pixii, who, in 1832, constructed a machine consisting of a permanent magnet, which he caused to revolve in front of the iron cores of a pair of bobbins, forming an electro-magnet. This invention was improved by other workers in the field of science, especially by Saxton and Clarke, both of whom suc- ceeded in producing very useful electric generators, in which the mechanical arrangement is the reverse of that in Pixii's i. e., the magnets are fixed and the coils of wire movable. And it is on this plan that all the subsequent machines have been con- structed, as affording better results than where the coils are stationary and the magnets movable. A great improvement was made in 1857, by Dr. W. Siemens, of Berfin. It consisted essentially in a new form of armature, which, owing to its simplicity and cheapness, is still used for many purposes, especially for electro-plating and laboratory work. It is composed of a cylinder of iron in which deep longi- tudinal grooves are cut resembling in section the letter H. In these grooves is wound lengthwise a single coil of wire, the two ends of which being joined to a split tube of copper on the axle form the commutator, from which the current is taken off by brushes or springs rubbing against it. By this longitudinal arma- ture the advantage is gained of cutting the greatest number of lines of force when rotated between the poles of a series of ad- jacent magnets. One of the most important inventions for the construction of electrical machines is the ring conductor by Pacinotti (1860). With the use of this ring conductor continuous currents of the same direction can be produced without the assistance of a commutator. Next in order comes the important discovery made simulta- ously, but independently, by Dr. W. Siemens and Sir C. Wheat- stone a discovery which marks the transition of the magneto- electric machine to that type most in practice at present the dynamo machine, called for convenience the dynamo. What Siemens and Wheatstone discovered was this : That a current 5 66 ELECTRO-DEPOSITION OF METALS. of electricity could be generated in the coils of the armature by the feeble residual magnetism in the iron cores of the elec- tro-magnets, and that by passing this feeble current round the magnets their magnetism would be strengthened, which in turn would produce a stronger current in the armature, and this cur- rent would again react on the magnets, rendering them more powerful, this action going on until the limit of saturation is at- tained. For it must be understood that this mutual accumulation cannot go on indefinitely, the magnetism in the iron cores can- not be intensified beyond a certain point, and this point depends on and is controlled by the scientific conditions on which the machine is constructed. Machines constructed on this principle are called, as stated, dynamo machines, to distinguish them from those previously used in which the magnets were permanently magnetized, thus causing the division of electric generators into two great classes, viz., magneto and dynamo machines, which are subdivided into two varieties one called the continuous current machine, fur- nishing currents in the same direction, and the other the alter- nating current machine, wherein the current is rapidly reversed or its direction changed many times a minute. An essential difference between continuous and alternating current machines is that the former may be self-exciting, whereas the latter must have a separate excitor or must be a magneto machine. The cores of the electro-magnets, it may be mentioned, are of cast iron, in which there is always a feeble residual magnetism. It is also easier to magnetize iron than steel, although, when the latter is once magnetized, it retains its magnetism for an indefinite period. It is not within the province of this work to describe in detail all the forms of dynamos, it being sufficient for our purpose to discuss those which are adapted to and are used for electro- plating uses. If we mention the Gramme machine first, it is not because it is superior to other machines, but because M. Gramme, its inventor, was the first to utilize the idea suggested by Dr. Pacinotti, of using an iron ring as a revolving electro- GALVANIC ELEMENTS. 6/ magnet, which, in place of having fixed revolving poles, had poles which traveled continuously through the whole circum- ference of the ring. Fig. 28 shows the Gramme armature in such a way as to allow its construction to be seen. The core or centre of the ring consists of a bunch of soft iron wires. The wire system wound about the core is formed of different spools, the initial wire of which is soldered to the terminal wire of the neighboring spool, so that all the spools of the ring form a single uninter- rupted conductor. The soldered places lie all on one side of FIG. 28. the ring, and are fastened to flat copper strips bent at right angles and insulated from one another by a non-conducting mass which forms the commutator through which the axle passes. The armature revolves between the poles of the electro- magnets secured to the sides of the machine, as shown in Fig. 29. As the ring is revolved a current is generated and flows out with every change in its position. The current so made is carried out by wire brushes which press upon the terminal plates of the wires in the ring. In the modern Gramme dynamos (Fig. 30) for galvano- plastic purposes, which have to furnish a considerable volume of current of slight electro-motive force, the inducting magnets are surrounded by broad copper bands instead of being wound 68 ELECTRO-DEPOSITION OF METALS. about with copper wire, and the armature is built up of stout copper rods, because the less resistance the copper windings have the greater the volume of current which is produced, while, vice versa, the tension increases with their resistance. Hence, machines for electro-plating purposes, which have to furnish quantities of current of slight tension, are wound about with FIG. 29. stout copper wire, while those for illuminating purposes, which must furnish currents of high tenison, are wound about with thin copper wire. For this reason machines constructed for galvano-plastic use and for nickeling, coppering, brassing, etc., are not suitable for illuminating purposes, and vice versa, ma- chines constructed for electric lighting cannot suitably be em- ployed for plating purposes. A disadvantage of the Gramme machine is that the only por- tion of the copper windings on the outside of the ring conductor GALVANIC ELEMENTS. 6 9 is in the magnetic field of the poles of the electro-magnets, so that only a comparatively small portion of the inductor is ex- posed to the inductive action of the magnets. Hence, in order to furnish correspondingly strong currents, the ring inductor must revolve very rapidly, the three sizes or numbers of Gramme machines mostly employed for galvano-plastic purposes making FIG. 30. in fact from 1500 to 2000 revolutions per minute, whereby the bearings are more rapidly worn out than with machines running at less speed, and, besides, more power is consumed. This evil led S. Schuckert, of Nuremberg, to construct a ma- chine in which Ziflat ring is successfully used as an inductor, which stands almost entirely under the inductive influence of the electro-magnets. Schuckert's flat ring machine is shown in Fig. 31. The core of the machine consists of thin sheet rib- ands insulated one from another, whereby greater solidity is 70 ELECTRO-DEPOSITION OF METALS. attained. The commutator and brushes are similar to those of the Gramme machine. The number of revolutions varies for the different size machines from 500 to 1500 per minute. It is almost noiseless in action and is exceedingly well constructed. The formation of sparks on the contact-surface of the brushes with^the commutator is scarcely perceptible, which secures the durability of the latter. FIG. 31. Fein, offStuttgart, has endeavored to overcome the defect of the Gramme machine in a different manner. In his machines thejpolar extensions of the magnets M and M 1 (Fig. 32) are elongated to a sort of drum, A A, which leads into the inter- ior of the inductor ring, whereby the greater portion of the windings is aiso brought into the magnetic fields of the electro- magnets. Closely resembling the Gramme machine in its general out- line, but differing materially in construction and action, is that known as'the Brush dynamo. Its armature, though consisting of a ring like that of Gramme's, is however, differently built up. At intervals around the ring a number of transverse grooves are formed, in which are wound the coils or bobbins, all in the GALVANIC ELEMENTS. same direction : and instead of forming a continuous circuit, as in theTGramme, each diametrically opposite pair of coils is FIG. 32. joined to each other by one end of each coil, while the other ends of the pair (i. e., the ends conveying the current) are con- FIG. 33. nected to the commutator. Fig. 33 illustrates the ring, showing the opposite coils joined up as described. Four coils are re- moved to show its construction. A series of deep concentric 72 ELECTRO-DEPOSITION OF METALS. grooves will be observed formed in the ring, their object being to reduce the mass of iron, and also to faciliate ventilation, thereby preventing the tendency to heat while the machine is working. Fig. 34 represents the complete Brush machine set in motion by a Brotherhood motor with three cylinders, the usual speed of the machine being about 750 revolutions per minute. The machines built by Siemens & Halske, in which the cylin- der-inductor invented by Hofner-Altenbeck is used, shows a different construction from those previously described. A de- FIG. 34. tailed explanation of the cylinder-inductor would lead us too far. It consists of a hollow iron cylinder, which revolves with the shaft, and about which the wires are wound parallel to the revolving axis in such a manner that no wire-windings are in the interior of the core (cylinder). The wire spirals wound about the cylinder are divided into sections, which' are so con- nected one with another as to form a single connected wire conductor. The terminal wires of the separate sections are connected to the segments of the commutator, so that both the currents generated in the wire system always meet from an opposite direction in two portions of the commutator opposite ('* GALVANIC ELEMENTS. 73 to one another. The commutator is constructed according to the Gramme system, and has, of course, as many segments as there are sections wound upon the cylinder. A real advantage of the machine is that the greater portion of the wire-windings of the cylinder-inductor is in the magnetic field. FIG. 35. Fig. 35 shows a Siemens & Halske magneto-electric machine with cylinder-inductor. Two series of 25 V-shaped magnets each are placed above and below, so that their poles of a similar name are opposite to one another, the poles of a similar name of the upper and lower magnets being connected one with another by arched pieces of soft iron. In the space thus formed between the upper and lower magnets, the cylinder-inductor revolves, the generated currents being carried away from the commutator by the brushes R and R'. In Siemens & Halske's dynamo- electric machines for electro- metallurgical purposes (Fig. 36) the plate magnets are wound about with square copper rods, in smaller machines with stout copper wire, while instead of spirals the inductor carries copper 74 ELECTRO-DEPOSITION OF METALS. ribands, which are connected with the commutator by suitably bent pieces. FIG. 36. Fig. 37 shows the Krottlinger machine constructed by Krott- linger, of Vienna. It consists of a strong iron base, P, from which rise two short cylindrical electro-magnets, M M, which have a semicircular shaft on the upper end N, and closely embrace the ring R. The standards L are cast in one piece GALVANIC ELEMENTS. 75 with the base P, and carry the bearing W W. The core of the ring R consists of separate disks of cast-iron arranged alongside one another upon the shaft so as to form a massive cylinder which is wound about with stout copper wire. The inductive spools of the ring are connected by means of screws with phos- phor-bronze plates of the commutator C. In this dynamo the current generated in the ring does not pass first through the electro-magnets, and then as working current into the con- ductor, but the greater portion passes as working current from the brushes B B into the conductor to the baths, while the other comparatively smaller portion of current passes through the wrappings of the electro-magnets M M, and excites them. As in Schuckert's machines, a regulator with resistance coils may be inserted in the circuit of the current, which allows of the generation of the current being controlled within quite wide limits, as may be desired. The advantages of this dynamo con- sist in the large masses of iron of short length with a large cross-section of the co'res of the electro-magnets, the standards and base being made in one piece, and in the durable iron core of the ring. The formation of sparks is slight. The Lahmeyer dynamo, shown in Figs. 38, 39, and 40, in FIG. 38. cross-section, open side view, and perspective exterior view, fulfils the three principal conditions of a good dynamo, viz., great useful effect, discharge of the current without sparks, and /6 ELECTRO-DEPOSITION OF METALS. solidity of construction. Opposite to the drum-anchor or drum- inductor of the machine stand horizontally two short and stout electro-magnet cores, whose ends averted from the anchor are connected by a thick iron frame carried above and below around the windings. This electro-magnet frame is made of soft cast-iron in one piece with the base of the machine, so that no resistance is offered to the lines of force by a joint, while the large iron cross-sections also give rise to but slight magnetic resistance. The magnetic field of the Lahmeyer machine must be con- sidered as a magnetic circle in so far as the lines of force which are generated by the spools in the iron everywhere contiguous to them pass together through both spools, and only ramify outside of them in the re-conducting plates B B f . By this favorable disposition, a current of slight strength passing FIG. 40. through the wrappings of the electro-magnets produces a strong excitation of the latter. The anchor has the shape of the Siemens cylinder, but is composed of disks of thin, white sheet-iron insulated one from the other by paper. Several segments of vulcanized fibre, two of which form the face, serve for holding the wrappings of the anchor. The latter consists of a single layer of stout copper wire, and this, in conjunction with the symmetrical disposition which excludes the scattering of the lines of force as much as GALVANIC ELEMENTS. 77 possible, effects a discharge of the current without sparks. The space visible in the side view is closed by perforated plates secured by screws, as seen in Fig. 40. This is a further ad- vantage of the machine in so far that all sensitive parts are protected from external injury. Like all cylinder or drum dynamos, the Lahmeyer dynamo requires a large number of revolutions per minute, but with the slight weight of the anchor, and the solid construction of the bearings, there is but little danger of the rapid wearing out of the latter. It may be of interest to give here a brief resume of what may be called the evolution of the dynamos for plating purposes in the United States, with special reference to the machines built by the Hanson & Van Winkle Co., of Newark, N. J. The first machine for electro-plating in the market was the Weston dynamo, Fig. 41, which was first manufactured in 1876. FIG. 41. Being of small dimensions, of compact form, and yielding an abundant current, it was well adapted to the wants of the elec- tro-plater, and hence it met with pronounced success, and to it can be traced the sudden development of electro-plating and electrotyping in this country. Many of these machines are still in use. An iron ring or cylinder attached to an iron base forms the outer shell of the machine. From the interior of this cylinder, 78 ELECTRO-DEPOSITION OF METALS. and projecting radially towards the centre of the apparatus, are aranged a number of magnets (usually five), which consist of a core of iron to which are fastened a number of thin tem- pered steel plates, and they are wrapped with insulated copper wire and so connected that the poles shall be alternately north and south. In the central space left between the inward ends of these magnets is arranged a shaft carried by bearings, which, to secure greater strength and perfect alignment, are cast on the iron disks or heads which are accurately fitted and bolted to the ends of the cylinder. To the shaft is secured a series of arma- tures made in segments. The armatures are of iron and also wrapped with wire. When revolved the outwardly projecting ends of these armatures will pass closely to, but without touching the inwardly projecting ends of the magnets. The commutator is made in two pieces, and requires but two springs to carry the currents from all the arma- tures. These springs or brushes are clamped in sockets pro- jecting from the front disk of the cylinder. An automatic switch or governor is attached to this machine for the purpose of pre- venting it from reversing by the polarization of the electrodes. FIG. 42. FIG. 43. In 1885, the ''Little Wonder" dynamo, Fig. 42, was intro- duced, and became very popular. In 1886, the Hanson & Van Winkle Co. began manufacturing the "Wonder" dynamo, Fig. 43. It embodied many new improvements and it was thought GALVANIC ELEMENTS. 79 perfection had been reached. However, in 1891, electrical sci- ence had developed so many entirely new features that the above mentioned firm brought out their H. & V. W. dynamo, shown in Fig. 44. K is the coil of the field magnet, A the re- volving armature, and C the commutator, BB are the brushes for picking up the currents of electricity produced in the arma- ture by revolving in the magnetic field and causing them to flow FIG. 44. in one direction. The current is not produced by friction. D is the lever to adjust the position of the brushes to the commu- tator. NN are ^ inch copper rods from the machine to the tank or to the main conductors on the wall. The binding-post on the machine marked P is joined to rods connected with the anodes, while N is connected to the object rods. The rods on the tank should be kept bright with emery paper. When but one tank is used, make direct connection in the same way after So ELECTRO-DEPOSITION OF METALS. getting the speed of the machine satisfactory for the maximum amount of work. The current may be decreased for small sur- iaces by moving the handle of the resistance board from the point marked " strong," one segment at a time, until it is found to answer. The position of the brushes, as shown in the cut, is the strongest point. By moving to the right or left the cur- rent is diminished. A slight change of position of the brushes is sometimes an advantage in setting the brushes when running on large surfaces, to avoid sparks. In using the resistance boards, (see later on) they are put up FIG. 45. as near the tank as possible the weak point being used when putting work in the tank, and then the strength of current is in- creased until the power required is obtained. The proper current for nickel-plating on brass or other GALVANIC ELEMENTS. 8l smooth surfaces, is when the gas is seen to adhere to the work, and there is no tendency to blacken edges. The new H. & V. W. dynamo, which is the latest improve- ment in plating dynamos manufactured by the Hanson & Van Winkle Co., of Newark, N. J., is shown in Figs. 45, 46, and 47. THE HANSON & VAWW/NKLE COMPANY. CA60 NEWARK. N.J Ntyv TO" This new slow-speed, iron-clad, compound-wound machine reaches the highest degree of excellence. The distinctive feature of this machine is the construction of the field magnets and of the frame, which are cast in one single casting. This FIG. 47. construction gives a magnetic field of much greater intensity than can otherwise be obtained, and entirely prevents all waste- ful induced currents in magnets and pole pieces, points of the greatest importance and essential to high efficiency. The magnetic circuit is of unusually low resistance by reason 6 82 ELECTRO-DEPOSITION OF METALS. of its shape, its shortness and the superior quality of iron used. There is no magnetism in the frame, base or shaft, as the mag- nets are supported at some distance from the base of the machine. There is, therefore, no opportunity for magnetic leakage, and besides the whole is enclosed by a shield or case of metal. The regulation of the voltage is entirely automatic, holding a constant voltage from no load to the full capacity of the dynamo. This result has heretofore been accomplished by the use of resistance rheostats, etc., requiring constant attention, in case the number of square feet of surface in the vats is varied, which is liable to burn the work if a light load is in the tanks. This has been overcome by the compound windings. A saving in the consumption of power required is also made, as the machine adjusts itself immediately to whatever load is placed thereon, from a single piece in the vats or to the full load of the dynamo. The armature is of a drum type and is built up of thin disks, all of which are securely fastened to the shaft. The winding is a modification of the Siemens method, and the mode of con- necting and collecting the current from the same produces a current as steady as any battery could give. The armature is so proportioned that it has but little idle wire over the heads and is only wound with one layer of wire. The winding is done with the greatest care, and so insulated that there is little danger of short circuiting and burning out. The ends of the armature and the electrical connections are thor- oughly covered, thereby protecting them from copper dust or dirt of any kind. The necessary voltage is secured by revolving a compara- tively small number of coils of wire in a powerful magnetic field, rather than by using a large number of coils and weak field, as is the usual practice. The small amount of wire on the armature accounts in a great measure for the absence of sparking at the brushes. The commutator is insulated with mica, and is of ample length GALVANIC ELEMENTS. 83 of surface to secure the best action and reduce the wear to a minimum. The segments are pure tempered copper, the most durable material known for the purpose, and when necessary may be removed without returning the machine to the factory. The shaft is made of the best crucible steel, of great diameter in its central part, accurately turned and finished in the best possible manner. All armatures of the same size are interchangeable. The slow speed of this dynamo is a most important point for consideration, it being run at about half the speed of other makes of plating machines of equal cost. The journals are of generous dimensions, resting in bronze bearings of the finest quality. They are self-aligning and self- oiling, with carrier rings in each bearing. The oil wells are of ample size to hold enough oil for two or three months' supply. In this manner the bearings are automatically oiled by the motion of the shaft, and they require no attention beyond a periodical examination and removal of oil. The advantages claimed by the manufacturers for this dynamo are as follows : i. High efficiency ; therefore economy of power. 2. Current generated without any sparking at the brushes ; therefore steady current, and small wear of brushes and commutator. 3. Solidity of construction ; therefore safety against interruptions from external injury, and no risk in trans- portation. 4. Accessibility of the different parts and simplicity of design. 5. No scattering of the lines of force; therefore no external magnetism or the attraction of pieces of iron, or the magnetizing of watches and compasses, etc. 6. Perfect regu- lation. 7. Self-oiling bearings. 8. Ninety-five per cent, effi- ciency. 9. Slow speed. 10. Self-aligning bearings, n. Me- chanical perfection. 12. Work equally well with light or heavy load, and will do more work for the same power and first cost than any other make of plating machines now on the market. Detailed descriptions of other machines, such as the Miiller, Mather, Elmore, Biirgin, Gulcher, etc., would needlessly lengthen this chapter. The great impulse which the art of XJNlVEBSlTT 84 ELECTRO-DEPOSITION OF METALS. electro-plating has in modern times received is largely due to the important improvements that have been made in the construction of dynamo-electric machines, by which mechanical energy generated 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 protected 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 troublesome to manage ; they only give out their full power when freshly charged, and as the chemical actions upon which they rely for their power progress, they deteriorate in strength and require frequent additions of acids and salts to be freshly charged, and their use demands constant vigilance and attention. Even when working on a small scale, it is cheapest to procure a small gas or other motor for driving a small dynamo, the lathes, and grinding and polishing machines. To make it possible for 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. 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. IV. PRACTICAL PART. CHAPTER IV. ARRANGEMENT OF ELECTRO- PLATING ESTABLISHMENTS IN GENERAL. ALTHOUGH rules valid for all cases cannot be given, because modifications will be necessary according to the size and extent of the establishment, the nature of the articles to be electro- plated, and the method of the process itself, there are, never- theless, certain main features which must be taken into con- sideration in arranging every establishment, be it large or small. 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 differ- ent 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 large establish- ments the room containing the baths should, besides 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. Due consideration must be given to the frequent 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. Especially unfavorable in this respect are smaller establishments working with batteries, in which the vapors evolved from the latter are added to the other vapors, and render the atmosphere injurious to health. (85) 86 ELECTRO-DEPOSITION OF METALS. 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 elements, it is recommended to place them in a closet varnished with asphalt or ebonite lacquer, 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. Since the baths work with greater difficulty, slower and more irregular below a certain temperature, provision for the suffi- cient heating of the operating rooms must be made. Except baths for hot gilding, platinizing, etc., the average temperature of the plating solutions 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 tem- perature of the baths cannot fall below the minimum even during the night, otherwise provision for the ready restoration of the normal temperature 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 consider- ation that they show in the evening a temperature of 64.5 to 68 F., and if the room is not too much exposed, the tempera- ture, especially of large baths, will only in rare cases be below 59 F. For greater security the heating pipes may be placed in the neighborhood of the baths ; if this should not suffice to protect the baths from cooling off too much, it is advisable to locate in the operating room a steam conduit of small cross- section fed from the boiler and to pass steam for a few minutes through a coil of metal indifferent to the plating solution sus- pended in the bath. In this manner baths of 1000 quarts, which, on account of several days' interruption in the opera- ELECTRO-PLATING ESTABLISHMENTS. 87 tion, had cooled to 36 F., were in ten minutes heated to 68 F. For smaller baths it is better to bring a small por- tion of them in a suitable vessel to the boiling-point, over a gas flame, and add it to the cold bath, and if, after mixing, the temperature of the bath is still too low, repeating the operation. Another important factor for the operating rooms is the con- venient 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 " Preparation of the Articles." Large establishments should, therefore, be provided with pipes for the admission and discharge of water, one conduit termina- ting 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. In consequence of rinsing and transporting the wet articles to the baths much moisture collects upon the floor of the oper- ating 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 water. Wood floors cannot be recommended, at least for large establishments, since the con- stant 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 saw-dust, frequently re- newed, or the articles when taken from the rinsing water or bath be conveyed to the next operation in small wooden buckets or other suitable vessels. The operating room should be of such a size as to permit the 88 ELECTRO-DEPOSITION OF METALS. 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 pro- cesses to be executed in it, the size and number of articles to be electro-plated 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 passage- way at least twenty inches wide, for the table where the arti- cles are freed from grease, for the lye kettle, hot-water reser- voir, saw-dust receptacle, tables for tying the articles to hooks, etc. 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 parti- tion, because in the preparatory grinding with emory, which is done dry, without the use of oil or tallow, the air is impreg- nated with fine particles of emery, which settle upon the polish- ing disks and materials, and in polishing soft metals cause fine scratches and fissures injurious to the appearance of the articles and difficult to remove by polishing. Hence, all operations re- quiring the use of emery, or coarse grinding powders, should be performed in the actual grinding- room, as well as the grind- ing upon stones and scratch-brushing by means of rapidly re- volving steel scratch-brushes. Articles already electro-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 disks of felt, flannel, etc., and the use of -polishing powders, or polishing compositions, im- part to the articles the final lustre before and after electro-plat- ing. The formation of dust in the polishing rooms is gener- ally over-estimated ; it is, however, sufficiently serious to render ELECTRO-PLATING ESTABLISHMENTS. 89 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 dis- turbing phenomena. In rooms in which large surfaces are polished with Vienna lime, as, for instance, nickeled sheets, the dust often seriously affects the health of the polishers, especially in badly ventilated rooms, and in such cases it is advisable to provide an effective ventilator. If this cannot be done, wooden frames covered with packing-cloth, placed oppo- site the polishing disks, render good service ; the packing- cloth, by being frequently moistened, retaining a large portion of the polishing dust. For grinding lathes requiring the belt to be thrown off in order to change the grinding, it is best to place the trans- mission carrying the belt-pulleys at a distance of about three feet from the floor; 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. ELECTRO-PLATING ARRANGEMENTS IN PARTICULAR. The actual electro-plating plant consists of the following parts : i. The sources of current (batteries or dynamo-electric ma- chines) with auxiliary apparatus. 2. The current-conductors. 3. The baths, consisting of the vats, the plating solution, the anodes, and the conducting rods with their binding-screws. 4. The apparatuses for cleansing, rinsing, and drying. The sources of current have already been discussed in Chapter III. p. 32, and the laws governing the suitable coupling cf the ele- ments on p. 19. A. Arrangement with elements. In working with elements it is first necessary to have a clear idea of the area of the articles which are to be at one time electro-plated in a bath, and of the magnitude of the resistance opposed by the bath to the current. go ELECTRO-DEPOSITION OF METALS. This and the size of the anodes show how many elements must be put together for a battery, and how the elements are to be coupled. Suppose we have a nickel bath which requires for its decomposition a current of 2.5 volts of electro-motive force or tension ; now since, according to p. 40, a Bunsen element yields a current of 1.88 volts, the reduction of the nickel can- not be effected with one such element, but two elements must be coupled for tension one after the other, whereby, leaving the conducting resistance of the wires out of consideration, an electro-motive force or tenson of 2x1.88=3.76 volts is ob- tained, with which the decomposition of the solution can be effected. If, on the other hand, we have a silver bath which requires only y 2 volt for its decomposition, we do not couple two elements one after the other, because the electro-motive force of a single element suffices for the reduction of the silver On p. 19 it has been seen that by coupling the elements one after the other (coupling for tension) 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 elements must be coupled alongside of one another (coupled for quantity). Hence in a group of, for instance, three elements coupled one after another, only one single zinc surface of the elements 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 elements to be brought into action must be, and, if for baths with medium resistance, it may be laid down as a rule that the effective zinc surface must be at least as large as the area of the articles ; provided the surface of the anodes is at least equal to the latter, the approximate num- ber of elements and their coupling for a bath can be readily found. Let us take the nickel bath, which, as above mentioned, requires a current of 2.5 volts, and for the decomposition of which two elemenfs must, therefore, be coupled one after the other, and suppose that the zinc surface of the Bunsen elements is 500 square centimetres, then the effective zinc surface of the ELECTRO-PLATING ESTABLISHMENTS. 9 1 two elements coupled one after the other will also be 500 square centimetres; hence a brass sheet 20x25 = 500 centi- metres can be conveniently nickeled on one side with these two elements, or a sheet 10x25 = 250 centimetres on both sides. Now suppose the surface to be nickeled were twice as large, FIG. 48. then the two elements would not suffice, and a second group of two elements, coupled one after the other, would have to be joined to the first group for quantity as shown in Fig. 4, or perspectively in Fig. 48. Three times the object surface would require three groups of elements, and so on. However, this, to a certain extent, empirical determination of the number of elements required for plating surfaces of definite measure may be abandoned, and we may avail ourselves of a more exact determination according to electrical values, since at the present time the electrical relations of the baths are accurately known and the performances of the elements as well as of the dynamos are specified according to current quantity and current tension. As regards the result of the process of deposition, the first requisite which has to be taken into account is that a sufficient quantity of current acts upon, the surface to be plated, and the next that the current possesses the necessary tension for the decomposition of the bath. , Now the current quantity which is required for the correct formation of the deposit upon I 92 ELECTRO-DEPOSITION OF METALS. square decimeter * =10x10 centimeters f ( 100 square centi- meters) may be designated as the current-density, and in the plating processes described later on, the suitable current-density is always given. If now, for instance, this current-density for a nickel bath is O.6 ampere per sq. dcm., the tension 2.5 volts and the largest surface to be plated in the bath 50 cm.X2O cm. = 1000 sq. cm. or 10 sq. dcm. a current-strength of at least 0.6X10=6 amperes would be required. Hence, a medium- large element furnishing 8 amperes would suffice if the tension necessary for the decomposition of the electrolyte did not amount to 2.5 volts. As previously stated, a Bunsen element furnishes about 1.8 volts, and hence, in order to obtain the higher tension, two elements must be coupled one after the other, and the excess, which would be an impediment to the correct formation of the deposit, has to be destroyed by the current-regulator to be described later on, in case it is not pre- ferred to increase the object-surface. For silvering, the current-density amounts to 0.25 ampere, and, with a slight excess of potassium cyanide, the silver bath requires I volt. If now, for instance, an object surface of 55 sq. dcm., which is about equal to 50 large soup-spoons, is to be silvered, 55x0.25=13.75 amperes and I volt are required. Hence, two elements of 8 amperes each must be coupled along- side one another in order to obtain 16 amperes current-quantity, and the excess destroyed by the current-regulator. In giving these illustrations it is supposed the objects are to have a thick solid plating ; for rapid plating with a thin deposit a different course has to be followed. Only a slight excess of electro-motive force in proportion to the resistance of the bath being in the above-mentioned case present, reduction takes place slowly and uniformly without violent evolution of gas on the objects, and by the process thus conducted the deposit formed is sure to be homogeneous and dense, since it absorbs but slight * i square decimeter (sq. dem.) =15.501 square inches. t i centimeter (cm.) =0.394 inch. ELECTRO-PLATING ESTABLISHMENTS. 93 quantities of hydrogen, and in mosf cases it can be obtained of sufficient thickness to be thoroughly resistant. If, however, the operation is to be executed quickly and without regard to great solidity and thickness of the deposit, the elements have to be coupled so that the electro-motive force is sufficiently large for the current to readily overcome the resistance of the bath. This is attained by coupling three, four, or more elements one after the other, as shown in the scheme Fig. 2. However, such de- posits can never be homogeneous, because they condense and retain relatively large quantities of hydrogen. As regards the filling and other management of the batteries, the reader is referred to pp. 37-43, under Bunsen elements. Having seen how many elements are required, and how they have to be coupled to form a battery for certain purposes, we will next consider the auxiliary apparatuses. Only in very rare cases will it be possible to always charge a bath or several baths with the same object-area; 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, areas will be suspended in the bath. Now, sup- pose a battery suitable for a correct deposit upon an area of, say five square feet, has been grouped together; and, after empty- ing the bath, a charge only half as large is introduced, the cur- rent of the battery will, of course, be too strong for this reduced area, and there will be danger of the deposit not being homo- geneous and dense, but forming with a crystalline structure, the consequence of which, in most cases, will be slight adhesive- ness, if not absolute uselessness. With sufficient attention the total spoiling of the articles might be prevented by removing the objects more quickly from the bath. But this is groping in the dark, the objects being either taken too soon from the bath, when not sufficiently plated, or too late, when the deposit al- ready shows the conseqences of too strong a current. To control the current an instrument called the rheostat, cur- rent-regulator, resistance board, or switch board, has been con- ducted, which allows of the current-strength ,of a battery being 94 ELECTRO-DEPOSITION OF METALS. reduced without the necessity of uncoupling elements. It is evident that the current of a battery, if too strong, can be weakened by decreasing the number of elements forming the battery, and also by decreasing the surface of the anodes, be- cause the external resistance is thereby increased. This coup- ling and uncoupling of elements is, however, not only a time- consuming, but also a disagreeable labor; and it is best to use a resistance board, with which by the turn of a handle, the desired end is attained. Figs. 49 and 50 show this instrument. Fig. 49. To the Bath TotheBqtfu Its action is based upon the following conditions : As ex- plained on p. 21, 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 re- sistance board consists of metallic spirals which lengthen the circuit, contract it by a smaller cross-section, and by the nature of the metallic wire have a resistance-producing effect. For a slight reduction of the current, copper spirals of various cross- ; ' ELECTRO-PLATING ESTABLISHMENTS. 95 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, 49 the conducting wire coming from the battery goes to the screw on the left side of the resistance board, which is connected by stout copper wire with the first contact-button on the left; hence by placing the metallic handle upon the button furthest to the left, the current passes the handle without being reduced, and flows off through the conducting wire secured in the setting-screw of the handle. By placing the handle upon the next contact-button to the right, two copper spirals are brought into the circuit; by turn- ing the handle to the next button, four spirals are brought into the circuit, and so on. By a 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. To control the reduction of the current effected by the resist- ance, a galvanometer is placed behind it. It consists of a mag- netic needle oscillating upon a pin, below which the curren ist conducted through a strip of copper, or, with weaker currents, through several coils of wire. The electric current deflects the magnetic needle from its 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 elements, it is of advantage to use a horizontal galvanometer (Fig. 51). It is screwed to a table by means of a few brass screws in such a po- F IG. 5 1 - sition that the needle in the north position, which it occupies, points to o w r hen no current passes through the instrument. Articles of iron and' steel must, of course, be kept away from the instrument. For stronger currents, it is better to combine a vertical galvanometer with the resistance board and fasten it to the same frame, as shown in Fig. 50. The screw of the handle of the resistance 9 6 ELECTRO-DEPOSITION OF METALS. board is connected with one end of the copper strip of the ver- tical galvanometer, while the other is connected with the screw on the right side of the resistance board in which is secured the wire leading to the bath. The resistance board and galvano- meter are placed in one conducting wire oniy, either in that of the anodes or of the objects ; one of these wires is simply cut, and the end connected to the battery is secured in the setting- screw on the side of the resistance board marked " strong," while the other end which is in connection with the bath is se- cured in the setting-screw on the opposite side marked " weak." The entire arrangement will be perfectly understood from Figs. 52 and 54. FIG. 52. Fig. 53 shows an improved switchboard or rheostat, which has twice the carrying power of other resistance boards for this purpose, it having sufficient length of wire to allow of toning down the highest electro-motive force used in plating, to the lowest figure called for, without showing heat or any unfavor- able symptoms. By the use of this switchboard the output from a plating room using two or more tanks can be doubled, provided the dynamo has the current capacity. ELECTRO-PLATING ESTABLISHMENTS. 9/ All platers understand that different voltages are required to operate successfully different kinds of solutions, and that when a sufficient voltage is to be generated for a solution of the highest resistance, and at the same time utilized in low resist- ance solutions, the tank nearest the dynamo, with the ordinary method, receives the most current, and a tendency to burn and blacken is noticed to a marked de- gree. When metals such as silver and copper are to be deposited in connection with such metals as nickel and brass, a higher electro- motive force is required, and a con- siderable drop in voltage is de- manded in the lower resistance solution so as not to blacken the work. With the old style switch- boards this is done at a great loss of current and work capacity of tank. With the old style switch- boards about the greatest carrying capacity that they will feed is from 25 to 35 amperes, not over 35 amperes. This deficiency is due to the smallness of the resistance wire and lack of suffi- cient metal conductivity. With the improved switchboard three times the current can be conveyed without showing the least heat in either the resistance wires, segments, switch or base- plate. Having discussed the advantages derived from the use of the resistance board, it remains to add a few words regarding the indications made by the galvanometer. Since the greater de- flection of the needle depends, on the one hand, on the greater current-strength, and, on the other, on the slighter resistance of the outer closing arc (conducting wires, baths, and anodes), it is evident that a bath with slighter resistance, when worked with the same battery and containing the same area of anodes and objects, will cause the needle to deflect more than a bath of greater resistance under otherwise equal conditions. Hence the deductions drawn from the position of the needle for the 7 9 8 ELECTRO-DEPOSITION OF METALS. electro-plating process are valid only for determined baths and determined equal conditions, but with due consideration of these conditions are of great value. Suppose a nickel bath always works with the same area of objects and of anodes, and FIG. 54. experiments have shown that the suitable current-strength for nickeling this area 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 handle of the resistance board will have to be turned so far to the right that the needle, in consequence of the introduced resistances, returns to 15. Now if, after working for some time, the battery yields a weaker current, the needle, since the resistance remains the same, will constantly retrograde, and has to be brought back to 15 by turning the handle to the left, when a current of equal strength of the former will again flow into the bath. This play is repeated until finally the handle stands upon the button furthest to the left, at which position the current flows directly into the bath without being influenced by the resistances of the resistance board. If now the needle retrogrades below 15, it is an indication to the operator that ELECTRO-PLATING ESTABLISHMENTS. 99 he must renew the filling of the battery if he does not prefer suspending fewer objects in the bath. For this reduced object^ area it is no longer required for the needle to stand at 15 in order to warrant a correct progress of the galvanic process, since the resistance being in this case greater, a deflection to 10, or still less, may suffice. This illustration will sufficiently show 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 area of objects and of anodes, and distance between them. An operator to be sure in this respect, and, above all, wishing to work scien- tifically, will replace the galvanometer by a voltmeter, which indicates the absolute magnitude of the electro-motive force passing into the bath, as will be explained later on. It frequently happens that in consequence of defective con- tacts with the binding-screws of the battery, or by the conductors 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 immediately indicated by the galvanometer, the needle be- ing not at all deflected in the first case, while in the latter the deflection will be entirely different from the usual one. The magnetic needle of the galvanometer also furnishes a means of recognizing the polarity of the current. If the galvanometer be placed in the positive conductor by securing the wire com- ing from the battery in the binding-screw on the south pole of the galvanometer, and the wire leading to the bath in the bind- ing-screw on the north pole of the needle, the needle, accord- ing to Ampere's law, will be deflected in the direction of the hands of a watch, i. e., to the right if the observer stands so in front of the galvanometer as to look from the south pole towards the north pole, because the battery current flows out from the positive pole through the conducting wire, anodes, and fluid to the objects, and from these back through the object wire to the negative pole of the battery. If now in con- sequence of the counter- current formed in the bath by the IOO ELECTRO-DEPOSITION OF METALS. metallic surfaces of dissimilar nature (see later on), and flow- ing in an opposite direction to that of the battery-current, the latter is weakened, the needle will constantly further retrograde from the zero point, and when the counter or polarizing cur- rent 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. The observing practical electro-plater will know that the character of a deposit obtained in a certain solution with a defi- nite area of objects to be plated depends largely upon the re- production of certain conditions, and especially upon the density of the current for the certain area to be plated. To reproduce such conditions it is highly important that either the electro- motive force existing between anode and cathode, or the current flowing through the same, be accurately measured. The ordinary galvanometer is insufficient and often misleading, and not at all satisfactory for the actual measurement of either the voltage or current. It indicates only a change of polarity, a cause of trouble not often accurring with the use of a good dynamo. If it is desired to measure the actual E. M. F. existing at the ter- minal of the dynamo or bath, only the very best voltmeters or ammeters should be used. They should be so constructed as to indicate quickly and accurately any sudden changes in current, and should be direct reading in volts and amperes, and their indications should not be subjected to gradual changes. A sensitive voltmeter such as the Weston voltmeter shown in Fig. 55, will indicate the slipping of belts, short circuiting in tanks and any irregularities in power. These voltmeters have a scale from o to 6 volts and upwards. The scale is divided into 120 divisions so that each division represents yf^ of a volt and when used in cannection with the switch board, Fig. 54, will enable the plater to study carefully all the requirements that insure good results, and will give him the means of accurately repro- ducing such conditions as he has found by experience con- ELECTRO-PLATING ESTABLISHMENTS. 101 ducive to success. One voltmeter can be made to answer for a number of tanks by means of a shunt from which the wires run to each tank. By this arrangement, and in connection with the FIG. 55. Switch-boards, the voltage for each tank and the current passing through the tank are controlled. Whilst it will be sufficient in most cases to use a voltmeter in combination with a rheostat for regulating purposes, it will sometimes be found desirable to determine the actual amount of current in amperes passing through a tank. It is a funda- mental law of electrolysis that a certain number of amperes passing through a plating solution will cause a definite weight of metal to be deposited. So, for instance, one ampere will 102 ELECTRO-DEPOSITION OF METALS. deposit in one hour 1.106 grammes of nickel, or 4.05 grammes of silver. It is evident, therefore, that by means of an accurate ammeter, the amount of metal actually deposited can easily be determined. The Weston ammeter, shown in Fig. 56, is very sensitive, indicating the slightest variation of current accurately FIG. 56. and with absolute certainty. It is, especially for higher ranges, the best, the most economical, and at the same time the cheapest instrument in the market. Both the Weston volt- meter and the Weston ammeter are furnished by Hanson & Van Winkle Co., Newark, N. J. From what has been said in this chapter and in the theoret- ical part, it is self-evident what rules have to be observed in conducting the current. Since the current-strength is weak- ELECTRO -PLATING ESTABLISHMENTS. 103 ened by resistance, the cross-section of the current-carrying wire as well as of that leading to the objects and to the anodes must be of a size corresponding to the current-strength, and the material for the wires should possess as high a conducting power as possible. Chemically pure copper is best suited for this purpose. Some information for calculating the thickness of the wires will be found at the end of the section " Arrange- ment with Dynamo Machines." The positive or anode wire effects the connection between the anodes of the bath and the positive pole (anode or carbon pole) of the battery, while the negative or object wire brings the objects in the bath into metallic contact with the negative (zinc) pole of the battery. As previously mentioned, the re- sistance board with galvanometer is placed in one or the other of the wires. For conducting the electric current to the baths, metallic wires, bands, spirals, or ribbons are used. The conducting wires are either employed in their natural metallic state, or are covered with some insulating or poorly conducting substance, such as cotton, silk, India-rubber, gutta-percha, and various varnishes. It is evident that covered wires should be bare and clean at their extremities where they are connected with the battery and with the anodes and objects to be plated. Wires of pure, well-annealed copper possess the best conducting power, and should have a sectional area capable of carrying the maximum quantity of current without offering appreciable resistance. Cables should be chosen where a large volume of current must be carried, they being more flexible than wire of a large size, and can be more easily laid. Insulated wires may come in contact with each other with- out inconvenience. Such, however, is not the case with bare wires ; because the electricity will pass through the shortest circuit and will not go through the bath if the two wires are in metallic contact. Such contact should, therefore, be carefully avoided. Vats or tanks. These are the vessels to hold the plating 104 ELECTRO-DEPOSITION OF METALS. solutions. Their shape may be either circular, square, or rectangular. They should be perfectly tight, impervious to the solutions, and unacted upon by them. They are made of different materials stoneware, glass, or porcelain vats being best, but they are the most fragile and expensive. Wooden vats must be carefully constructed, and are best secured at the ends by bolts and nuts, as shown in Fig. 57, which serve to hold the sides firmly against the end pieces. FIG. 57. The vat 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 I ^ each of stearin and linseed oil, melted together and incorporated. For large acid copper and nickel baths wooden vats lined with chemically pure sheet-lead about 0.118 inch thick, and the seams soldered with pure lead, are very suitable. Care must, of course, be taken that neither the conducting rods nor the articles suspended in the bath and the anodes come in con- tact with the lead lining, which with some care can be readily avoided. Objections have frequently been made to such vats, but in Dr. George Langbein's establishment they have for six ELECTRO-PLATING ESTABLISHMENTS. 1 05 years been used for nickel baths without the lead having the slightest effect upon the baths, and no disturbance in the work- ing of the latter has ever been observed. After careful investi- gation such lead -lined vats have even 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. Only for nickel baths containing large quantities of acetates, citrates and tartrates these lead-lined vats cannot be recom- mended, 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 correcting the reaction of a nickel bath need not be taken into consideration. The lead-lining might be dispensed with if it were not for the difficulty of keeping wooden vats tight. Many plating solutions impair the swelling power of the wood, and with even a slight change in the tem- perature the vats become pervious, the evil increasing in time. Vats 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 vats. 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. A very useful vat is one of iron enameled with white acid- proof enamel. Such vats are made in different shapes and sizes up to 5^ feet long, 24 inches wide and 19 inches deep.. For gold and other solutions an agate vessel is recom- mended, this material standing cyanide solutions, acids, etc. The vats for heating baths are best made of enameled iron or of wood lined with sheet lead. Stoneware vats do not bear heating. It is advantageous to provide the narrow sides of the vats with semicircular notches for the conducting rods to rest in, to prevent their rolling away. When using stoneware vats the ELECTRO-DEPOSITION OF METALS. conducting rods are laid directly upon the vats. Vats of other material must be provided with an insulated rim of wood, or the rods are insulated by pushing a piece of rubber hose over their ends. According to the size of the bath, 3, 5, 7, or more conducting rods, best of pure, massive copper, are used. To secure the uniform coating of the objects with metal they must be surrounded as much as possible by anodes, i. e., the positive pole plates of the metal which is to be deposited. For FIG. 58. No. No. 2. No. 4. 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 centre rod. For wide baths five conducting rods are frequently used, but they should always be so arranged that a row of objects is be- tween 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 ELECTRO-PLATING ESTABLISHMENTS. lO/ FIG. 59. FIG. 60. to be uniformly plated on all sides, because the sides turned towards the anodes are coated more heavily than those sus- pended opposite to the other row of objects. For large round objects it is better to entirely surround them with anodes, if it is not preferred to turn them frequently, so that all sides and portions gradually feel the effect of the im- mediate neighborhood of the anodes. (See " Nickeling.") For objects to be plated on one side only the centre rod may be used for the anodes, and the two outer ones for the objects ; the surface to be plated being, of course, turned toward the anodes. The rods carrying the anodes, as well as those carrying the objects, must be well connected with each other, which is effected by means of binding posts and screws of the improved forms shown in Fig. 58, Nos. I and 2 being rod connections for tanks. No. 2, or double connection, is a very convenient form as it can be adapted to so very many changes. The three-way connec- tion, No. 3, is so well known that it hardly needs an explanation. 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. 59) ; hooks of another soluble metal would contaminate the bath by dissolving in it, and this must be strictly avoided, as it would cause all sorts of disturbances in the correct working of the bath. In case hooks of another metal, except platinum, are used, the anodes must be hung so that they project above the surface of the liquid, and the hooks not being immersed are, therefore, not liable to corrosion ; but the anodes are then not 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. 60). 108 ELECTRO-DEPOSITION OF METALS. 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 of No. 20 Birmingham wire gauge (see Chapter XVIII. , "Useful Tables") 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 an- nealed and straightened for future use. To keep the rods clean and to protect them from the fluid draining off from the articles when taken from the bath, it is ad- visable to cover them with a roof of strips of wood ( / /\), 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. The plating solutions, briefly called baths, will be especially discussed in speaking of the various electro-plating processes. It still remains to consider the cleansing and rinsing apparatuses. Every electro-plating establishment, no matter how small, re- quires 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 cov- ered with cloth, which serves as a rest for the objects previously tied to wires. The objects are then scrubbed with a brush, or rubbed with a piece of cloth dipped in the cleansing agent. The latter is then removed by rinsing the objects in the water in the tub and drawing them through water in another tub. By this cleansing process a thin film of oxide is formed upon the metals, which would be an impediment to the intimate union of the ELECTRO-PLATING ESTABLISHMENTS. 109 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 cleansing processes three vessels with water, which has to be frequently renewed, as well as the necessary pots for pickling solutions, have to be provided. In case the vat for cleansing the articles or the box-like table (see Fig. 66) is provided with a rose-jet, under which the objects are rinsed, the other vats are not required. 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 vats or with the rose-jet, and finally have to be immersed in hot water until they have acquired the temperature of the latter. How the water is heated makes no difference, and depends on the size of the establishment. The heated objects are then immediately dried in a box filled with dry, fine sawdust that of maple, poplar, or other wood free from tannin being suitable for the purpose. B. Arrangements with dynamo-electric machines. For setting up and running the machines the following rules are to be ob- served. Larger machines are to be screwed to square wooden joists resting upon a solid brick foundation about six inches above the floor; smaller machines may be placed upon and fastened to strong tables secured to the floor or wall. The prin- cipal point is that the foundation or table is not subjected to shocks which would be transferred to the machines and cause, by the vibration of the brushes, a larger formation of sparks, and consequent greater wear of certain portions of the machine. Foundations about 8 inches wider on each side than the machine and built of brick and cement have been found most suitable. If possible, the machines should be located in the neighborhood of the baths they are to feed, since the greater the distance from the bath at which they are placed the larger the cross-section IIO ELECTRO-DEPOSITION OF METALS. of the principal conducting wire must be, and the more trouble- some the regulation of the current will prove, provided it is not intended to place another resistance board just in front of the bath, which is the best plan for regulating the curreut with the greatest nicety. It is best to set the dynamo in motion by means of a gearing with loose and fast pulley so as to render a gentle engaging of the machine possible, and not directly from the fly-wheel of the motor, whereby in consequence of the jumping and dragging of the belt it is apt to run less regularly. The bearings should be kept well lubricated, best with automatic oilers filled with good lubricating oil. The stated number of revolutions per minute should not be exceeded, since by the stronger current thereby generated the machine might become very hot and suffer injury. On the other hand, when a weaker current is required, the machine may be run more slowly than the maxi- mum performance with the prescribed number of revolutions. The brushes which conduct the current from the commutator should be firmly secured in their holders by means of screws, and the levers pressing them by means of spiral springs against the commutators must be fixed so that the brushes securely and uniformly slide upon them ; pressing the brushes too tightly against the commutators should, however, be avoided. While the machine is running the brushes should not be lifted off, since the large sparks thereby produced strongly attack the brushes and the commutator, and this favorite amusement of the workmen should be strictly for- bidden. When the machine is for the first time set in motion, the commutator should be gone over with a smooth file or emery paper to remove any projections of the insulation between the metallic plates, which readily swell when the machine stands in a damp place. The commutator should also daily be freed, by wiping, from copper-dust, and if after some time it wears unevenly, be made smooth with a file. The inductor ring should at least once every week be cleaned ELECTRO-PLATING ESTABLISHMENTS. Ill from copper-dust by means of a small bellows or other instru- ment. Movable articles of iron and steel should be kept away from the machine when running, as they might be attracted by the portions of the machine which have become strongly magnetic. The object- and anode-wires must be insulated from each other, as well as from the ground and damp brick-work by dry wood or porcelain, and the places of junction kept bright. The employment of special wire-carriers, of the form shown in Fig. 6 1, is advisable. They consist of cast-iron arms, pro- vided on the ends with a case, between the lower and upper cover of which are disks of hard rubber. To regulate the current resistance boards or current- regu- lators are used. They are constructed according to the same principles as those described under " Arrangement with Ele- ments " (p. 89), only the spirals are longer and of a larger cross-section, and the entire instrument is stronger. Instead of upon wood, the contact buttons are mounted upon slate plates, as wood would be carbonized by the spirals becoming hot. In case one machine has to feed several baths of dissimilar nature and composition, the regulation of the current for all the baths in the main conducting wire is not feasible on account of the different resistances ; and it will be neces- sary to place a resistance board in front of FlG * 6l< every bath. With dynamos of the Schuckert and Lahmeyer type, which are very practical, it will be further necessary to place a resist- ance board (the resistance board of the *^- dynamo) in the windings of the machine, in order to be enabled to generate more or less current, as may be required, and to avoid an unnecessary con- sumption of power. From the scheme Fig. 62, for such a machine, with its auxiliary apparatus, the main conducting wire and a few baths, the reader will readily see what is required. The dynamo resistance board will have to be placed so that the machine yields somewhat more current than with due con- TK*. 112 ELECTRO-DEPOSITION OF METALS. sideration to the object-area is required for all the baths, while the supply of current for each bath is regulated by the resist- ance board placed in front of it. In the scheme Fig. 62 are i + ELECTRO-PLATING ESTABLISHMENTS. 113 sketched two further instruments for measuring the quantity and the electro-motive force of the current ; by the first, called the amperemeter, or better ammeter, the whole current-strength can be directly read off in amperes ; and by the other, called the voltmeter, the electro-motive force or tension in volts. The ammeter is placed in one conducting wire only, either in that FIG. 63. f of the object or of the anodes, while the voltmeter is con- nected with both, one setting-screw being joined, on the points 114 ELECTRO-DEPOSITION OF METALS. where the tension is to be measured, to the object-wire by a O.O39-inch thick copper wire, and the other to the anode wire. In the sketch (Fig. 62), the voltmeter being directly in contact with the poles of the machine will indicate the tension produced by it. This mode of placing the measuring instruments is, how- ever, not suitable for establishments using baths of different compositions and different resistances ; in such case the tension must be measured on the bath itself, and consequently the volt- meter has to be placed in the conducting wire between the re- sistance board of each bath and the bath itself. However, for a large establishment, using many baths, it would be quite an item of expense to provide each bath with a special voltmeter. But this is not necessary, one voltmeter sufficing for three, four, or even more baths. In order conveniently to read off on the voltmeter the tension of the current passing into one of these baths a shunt is required, the coustruction of which is seen from Figs. 63 and 64. Fig. 64. Fig. 63 shows the coupling of the main object-wire ( ) and the main anode- wire ( + ), with the resistance boards R v and RV the voltmeter V, the shunt /", and the two baths. ELECTRO-PLATING ESTABLISHMENTS. 115 In Fig. 64 the coupling is enlarged, and upon this the fol- lowing 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 shunt U consists of a brass handle, mounted with a brass foot, upon a board ; in the foot is a screw, with which is connected by a o.O39-inch thick copper-wire one of the pole-screws of the voltmeter. The brass handle drags with spring pressure upon contact buttons connected by copper wire with the setting screws I, 2, 3, 4, 5 (upon the shunt board), which serve for the reception of the o.O39-inch thick insulated wires i, 2, 3, 4, for measuring the tension, which branch off from the various baths or resistance boards. The other pole-screw of the voltmeter is directly con- 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 R l ; the screw marked " weak " of the resist- ance board R 1 is connected by a correspondingly stout wire with the object-wire of bath I, and at the same time with the binding-screw I of the shunt. The resistance board R 2 , of the bath II, is in the same manner connected with the main object-wire, the bath, and the binding-screw 2 of the shunt; also the resistance boards R 3 and R 4 of the baths III and IV, which are not shown in the illustration. With the main anode- wire each bath is directly connected by leading the current to an anode- rod of the bath by means of binding-screws and a stout copper wire, and establishing a metallic connection be- tween this anode-rod and the next one. However, instead of connecting both, the current may also be led from the main anode-wire to each anode-rod. In the illustration, the handle of the shunt rests upon the second contact-button to the left, which is connected with the binding-screw 2 of the board. In the latter is secured the wire for measuring the tension of the resistance board R^ ; and hence the voltmeter V will indicate the tension of the current in bath Il6 ELECTRO-DEPOSITION OF METALS. II. Suppose bath II is full of objects, and with the position of the handle of the resistance board at " weak," as shown in the illustration, the voltmeter indicates 1.5 volts, while the most suitable tension for the bath is 2.5 volts, the handle of the re- sistance board is turned to the left until the needle of the volt- meter indicates the desired 2.5 volts. By turning the handle of the shunt U to the left, so that it rests upon the contact-button i, the measuring wire of bath II is thrown out, and the voltmeter indicates the tension in bath I. If the handle rests upon contact-button 3, the tension in bath III is indicated, and so on. In working the different baths in a larger establishment, each bath is best directly fed from the main conducting wire after the current has been brought to the proper strength by the resist- ance board. Coupling the baths one after another so that the current passes from one bath to the other is only practicable for metallurgical processes gaining of metals where every bath contains the same area of objects and anodes, has the same re- sistance, and works under the same conditions. Fig. 65 shows the ground plan of an electro-plating establish- ment. NN 1 is a dynamo-electric machine, with 300 amperes at 4 volts' tension. The resistance board belonging to the machine, which is placed in the conductor, is indicated by No. I, and is screwed to the wall. The main conductors, marked and -f , run along the wall, from which they are separated by wood, and con- sist 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 objeet-wire and anode-wire lead two wires, each 0.27 inch in diameter ; one end of each is bent to a flat loop and secured under the pole screws of the machine, while the other ends are screwed into the second bore of the binding-screws screwed upon each conductor. To the right and left of the machine the baths are placed ; Zn, indicating zinc bath ; Ni Ni, nickel baths, Ku, copper cyanide bath ; Mg, brass bath ; 5 K, acid copper bath ; Si, silver bath ; and Go, gold bath. Each of the ' first- ELECTRO-PLATING ESTABLISHMENTS. 117 named five baths has its own resistance board, designated by 2, 3, 4, 5, 6. However, before reaching the acid copper bath, and FIG. 65. / 7///../T77 V//////7-7 Jl8 ELECTRO-DEPOSITION OF METALS. the silver and gold baths, the current is conducted through two resistance boards, 7 and 8. Since these baths require a current of only slight electro-motive force, it is necessary to place two, and in many cases even three or four resistance boards, one after another, unless it be preferred to feed these baths with a special machine of less tension. From Fig. 65 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 tension. For want of space the gold bath is placed in the sketch be'hind the silver bath ; but as their resistance is not the same, they must also be placed parallel. t The coupling of the voltmeter and shunt is omitted in the illustration. Their arrangement will be understood from Fig. 63. 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. ' Instead of the preparatory cleansing with hot lye, which saponifies the oils, the objects may be brushed off with benzine, oil of turpentine, or petroleum, the principal thing being the removal of the greater portion of the grease and dirt, so that the final cleansing, which is effected with lime paste, may not require too much time and labor. It is also advisable to cleanse the objects, in one way or the other, immediately after grinding, as the dirt, which forms a sort of solid crust with the oil, is difficult to soften and to remove when once hard. The table for freeing the articles from grease stands alongside the lye-kettle, and is shown in perspective in Fig. 66. It consists of a box with legs, which is divided by four partitions into two large divisions, A and B, and three smaller ones, C, D, and E. The separate divisions are lined with sheet lead. Across divisions A and B boards covered with cloth are laid, upon which the articles are brushed ELECTRO-PLATING ESTABLISHMENTS. 119 for the final cleansing with lime paste. Over each of these divisions is a rose-jet, provided with a cock, under which the articles are rinsed with water. The discharge pipes from A and B are provided with valves, and are tightly soldered into the bottom of the box. Of the smaller partitions, D serves for Fig. 66. the reception of the lime paste, while C and E each contain two pots or small stoneware vats with pickling fluid. In Fig. 65 these vats are indicated by 1 1 and 12. The two marked I T contain dilute sulphuric acid for pickling iron and steel articles, while those marked 12 contain dilute potassium cyanide 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. The advantages of such a box-table are that everything is handy together ; that the pickle, in case a pot should break, cannot run over the floor of the workshop ; and that the latter is not spoiled by pickle dropping from the objects. The small box K, on the side of the table, serves for the reception of the various scratch-brushes. Between the lye-kettle L and the box-table in Fig. 65 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. 120 ELECTRO -DEPOSITION OF METALS. 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 another they cannot be im- mediately brought into the bath. H W is the hot water reservoir in which the plated objects are heated to the temperature of the hot water, so that they may quickly dry in the subsequent rubbing in the sawdust box Sp. Before polishing the deposits, iron and steel objects are thoroughly dried in the drying chamber T (Fig. 65), heated either by steam or direct fire. By finally adding to the appli- 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. If possible the plating-room should be on the ground floor and where it will receive the best light and ventilation, both being essential to good work. The room must also be provided with facilities for obtaining water and steam, as much of the work in plating is in preparing the article for plating by scouring and rinsing, and, with convenient facilities in doing this, the cost is reduced and better work accomplished. Where a plating plant is required, provision should be made for extension or de- velopment of trade. The dynamo should also be larger than absolutely necessary, as a plant can then be enlarged as required by adding one or more tanks, the other appliances remaining the same. Fig. 67 shows a plating-room arranged by the Hanson & Van Winkle Co., of Newark, N. J. The arrangement will be readily understood from the illustration, so that a detailed description is not necessary. What has been said in the preceding section in regard to the conducting wires, vats, conducting rods, anodes, etc., also ap- plies to establishments using electro-dynamo machines. In calculating the thickness of the conducting wires for dyna- mos, I square millimetre (o.ooi square inch) of conducting cross-section is to be allowed for every 3 amperes for so-called short circuits up to 20 metres (21.87 yards). This is valid for ELECTRO-PLATING ESTABLISHMENTS. 121 currents up to 500 amperes; for longer circuits I j to 2 am- peres are calculated for the square millimetre of conducting cross-section. FIG. 67. PLAT/M6 DS/G THE HAM50M & VAN WINKL E CO.. S CHICAGO MEWARK,N.J.. t/tV YORK CHAPTER V. TREATMENT OF METALLIC ARTICLES. THE objects having to undergo both a mechanical and chem- ical preparation, each of them will be considered separately. A. Mechanical Treatment. I. Before electro-plating. If the objects are not to be electro- plated while in a crude state, which is but rarely feasible, the mechanical treatment consists in imparting to them a cleaner surface by scratch-brushing, or a smoother and more lustrous one by grinding and polishing. It may here be explicitly stated that scratch-brushing of electro-plated objects is not to be con- sidered a part of their preparation, since such scratch-brushing is executed in the midst of or after the electro-plating process, its object being to effect a change of the electro-deposition in more than one direction, and not the cleansing of the surface of the metallic base. The following directions, therefore, apply only to scratch-brushing of objects not electro -plated. The scratch-brushing of electro-depositions will be considered later on. In regard to grinding, we have to deal with the subject only in so far as it relates to smoothing rough surfaces by the use of grinding powders possessing greater hardness than the metal to be ground ; with grinding in the sense of instrument- grinding, the primary object of which is to provide the instru- ment with a cutting edge, we have nothing to do. As some platers seem to have wrong ideas regarding the electro plating process, it may here be mentioned that the de- posit is formed exactly in correspondence with the surface of the basis metal. If the latter has been made perfectly smooth by grinding and polishing, the deposit will be of the same (122) TREATMENT OF METALLIC ARTICLES. 123 nature ; but if the basis-surface is rough, the deposit also will be rough. Hence it is wrong to suppose that by electro-plating a rough surface can be converted into a lustrous one, and that pores or holes in the basis-metal can be filled by plating. In order to obtain a deposit which is to acquire high lustre by polishing, it is absolutely necessary to bring the basis into a polished state by mechanical treatment. In doing this it is not necessary to go so far as to produce high lustre, but fine scratches which would be an impediment to attaining high lustre after plating must be removed. Scratch-brushing may be effected either by hand or by a scratch-brush lathe. In the first place scratch-brushes of more or less hard brass or steel wire, according the hardness of the metal to be manipulated, are used. Various forms of brushes are employed, the most common ones being shown in the accompanying illustrations (Figs. 68 to 76.) FIG. 68. FIG. 69. FIG. 70. FIG. 71. Fig. 75 shows swing brushes for frosting or satin finish, with lour knots of medium brass or steel wire, and Fig. 76 the plater's lathe goblet scratch-brush. I2 4 ELECTRO-DEPOSITION OF METALS. In scratch brushing it is recommended to remove, or at least to soften, the uppermost hard and dirty crust (the scale) by immersing the objects in a pickle, the nature of which depends on the variety of metal, so that a complete removal of all im- FIG. 72. FIG. 73. FIG. 74. FIG. 76. FIG. 75. purities and non- metallic substances may be effected by means of the scratch-brush in conjunction with sand, pumice-stone, powder, or emery. The work is complete only when the article shows a clean metallic surface, otherwise the brushing (scouring) must be continued. Scratch-brushes must be care- fully handled and looked after, and their wires kept in good order. When they become bent they have to be straightened, which is most readily effected by several times drawing the brush, held in a slanting position, over a sharp grater such as is used in the kitchen. By this means the wires become dis- entangled and straightened out. Hand scratch-brushing being slow and tedious work, large establishments use circular scratch-brushes which are attached to the spindle of a lathe. These circular brushes consist of round wooden cases in which, according to requirement, I to 6 or more rows of wire bundles (see Fig. 77) are inserted. TREATMENT OF METALLIC ARTICLES. 125 Brushes with wooden cases are, however, more suitable for scratch-brushing deposits than for cleansing the metallic base, since for the latter purpose a more energetic pressure is usually applied, in consequence of which the bundles bend and even break off, if the wire is anywise brittle. For cleansing purposes a circular scratch-brush, which the workman can readily re- furnish with new bundles of wire, deserves the preference. It is constructed as follows: A round iron disk about o.ii inch thick, and from 5f to 7f inches in diameter, is provided in the centre with a hole so that it can be conveniently placed upon the spindle of the lathe. At a distance of from 0.19 to 0.31 inch from the periphery of the disk, holes 0.079 to o.i I inch in diameter are drilled, so that between each two holes is a distance FIG. 77. of 0.15 inch. Draw through these holes bundles of wire about 3.93 inches long, so that they project an equal distance on both sides. Then bend the bundles towards the periphery, and on each side of the iron disk place a wooden disk 0.31 to 0.39 inch thick. The periphery of the wooden disk, on the side next to the iron disk, should be turned semi-annular, so that the wooden disks when secured to the spindle press very lightly upon the wire bundles, and the latter remain very mobile. When a circular scratch-brush constructed in this manner and secured to the lathe is allowed to make from 1800 to 2000 revolutions per minute, the bundles of wire, in consequence of the centrifugal force, stand very rigid, but being mobile will give way under too strong a pressure without breaking off, and can thus be utilized to the utmost. When required, the iron 126 ELECTRO-DEPOSITION OF METALS. disk can be refurnished with wires in less than half an hour. An error frequently committed is that the objects to be cleansed are pressed with too heavy a pressure against the wire brushes. This is useless, since only the sharp points of the wire are effective, the lateral surfaces of the bundles removing next to nothing from the articles. Brushes. A definition of these instruments is unnecessary, and we shall simply indicate the various kinds suitable to the different operations. The fire-gilder employs, for equalizing the coating of amalgam, a long-handled brush, the bristles of which are long and very stiff. The electro-gilder uses a brush (Fig. 78) with long and flexible bristles. For scouring with sand and pumice-stone alloys containing nickel, such as German silver, which are difficult to cleanse in acids, the preceding brush, with smaller and stiffer bristles, is used. The gilder of watch-works has an oval brush (Fig. 79), with stiff and short bristles for graining the silver. The galvanoplastic operator, for coating moulds with black- lead, besides a number of pencils, uses also three kinds of brushes the watchmaker's (Fig. 80), a hat brush, and a blacking-brush. The bronzer uses all kinds of brushes. FIG. 78. FIG. 79. FIG. 80. Brushes are perfectly freed from adherent grease by washing with benzine or bisulphide of carbon. In large establishments engaged in electro-plating cast-iron without previous grinding, the use of the sand-blast in place of the circular wire brush has been introduced with great ad- vantage. Objects with deep depressions, which cannot be reached with the scratch-brush, as well as small objects, which TREATMENT OF METALLIC ARTICLES. 127 cannot be conveniently held in the hand and pressed against the revolving scratch-brush, can be brought by the sand-blast into a state of sufficient metallic purity for the electro-plating process. However, while the revolving scratch-brushes impart to the objects a certain lustre, they acquire by the sand-blast a dead lustre, and, hence, the blast is also frequently used for the purpose of deadening lustrous surfaces to their entire extent, or of producing contrasts for instance, dead designs upon a lus- trous ground, or vice versa. Fig. 8 1 shows a sand-blast. The compressed air, whose FIG. 81. pressure must be at least equal to an 18^ inch column of water, passes through the blast-pipe A into a nozzle running horizont- ally through the machine, and carries away from there a jet of 128 ELECTRO- DEPOSITION OF METALS. sand, which falls into the outflowing blast and is hurled upon the objects placed under the nozzle. The objects rest upon sheet- iron plates or in boxes of sheet-iron, which, moving at a slow rate, pass under the nozzle ; the motion is effected by the shafts B B, with the use of belts. To prevent dust, the machine is encased in a wooden or sheet-iron case, a few windows allowing a view of the interior. The sand used in blasting collects in a box, and is returned to the sand-reservoir by an elevator. The jet of sand acts not only upon the upper side of the objects, which it strikes first, but also almost as energetically upon the lower, so that, as a rule, the cleansing process is com- pleted by one operation. Objects of a specially unfavorable shape must be passed twice or three times under the nozzle. Steam-jet sand blasts have recently been constructed, the action of which is based upon the same principle. However, in place of compressed air a jet of steam is used, the action of which is still more rapid. If a clean metallic surface is to be given at one time to a large number of small articles, such as buckles, steel beads, metal buttons, steel watch-chains, ferrules, etc., a tumbling drum or box is frequently used. It generally consists of a cylindrical or polygonal box having a side door for the introduction of the work, together with sharp sand or emery, and is mounted hori- zontally on an axis furnished with a winch or pulley, so as to be revolved either by hand or power, as may be desired. In order to prevent certain objects, like hooks for ladies' dresses and the like, from catching each other and accumulating into a mass, a number of nails or wooden pegs are fixed in the interior of the drum. A very practical form of tumbling drum, in which a change of position of the contents must constantly take place, is shown in Fig. 82. The drum A, of wood or iron, is obliquely placed upon the shaft B. The objects are introduced through the door C. The drum is revolved by a crank, or by a belt by means of the pulley D. All portions of the drum describe thereby ellipses, the walls of the drum being now raised (indi- TREATMENT OF METALLIC ARTICLES. 129 cated by the dotted lines) and then lowered, so that the objects in the drum are in constant motion and rub against each other. By introducing together with the objects a suitable polishing powder with oil or water, such drums may be used not only for the preparatory cleansing of the objects, but also for polishing. Fig. 83 shows the improved exhaust tumbling barrel manu- factured by the Hanson & Van Winkle Co., of Newark, N. J. It will be seen that the barrel is egg-shaped, that it has a sec- tion of exhaust pipe connected to the hollow journal at one end, and a tight and loose pulley at the other end. No gearing whatever is used. The special advantages of this tumbling barrel are found in the egg-shape. 1 . It gives the contents a double motion or action from ends to center and from sides to center causing a thorough mixing and rubbing together of all the parts contained therein, clean- ing and polishing the contents better and quicker than any other form of barrel. 2. It requires less power, as the end motion causes the con- tents at the ends to tumble into the center because of their as- suming the perpendicular earlier than the parts at the sides. 3. It runs with less noise, because the contents are kept mov- ing in two directions at the same time, doing away with the in- termediate motion so noticeable in other forms. Doing away with gearing also lessens the noise. The manufacturers claim that this barrel will do* double the work of any other of the same size in the same length of time. 9 130 ELECTRO-DEPOSITION OF METALS. It is lined with a sectional lining of hard iron, which can be cheaply and quickly replaced, making the barrel as good as new. A current of air is forced through the barrel by an ex- haust fan, which removes the dust and carries it out through pipes arranged for the purpose, and the room is kept perfectly free from this nuisance. For ordinary polishing the articles are brought into the FIG. 83. tumbling drums together with small pieces of leather waste (leather shavings), and taken out in one or two days. How- ever, to produce an actually good polish a somewhat more complicated method has to be pursued. The articles are first freed from adhering oxide by washing in water containing 5 per cent, of sulphuric acid, rinsed, and dried in a drying chamber or in a pan over a fire. They are next brought into the tumb- TREATMENT OF METALLIC ARTICLES. 131 ling drum together with the sharp sand, such as is used in glass-making, and revolved for about 12 hours, when they are taken from the drum and freed from the admixed sand by sift- ing. They are then returned to the drum, together with soft, fibrous sawdust, to free them from adhering sand, and at the same time to give them a smoother surface. They are now again taken from the drum, freed from sawdust and returned to the drum, together with leather shavings. They now remain in the drum until they have acquired the desired polish, which, according to the size and shape of the articles and the degree of polish required, may frequently take two weeks or more. Articles of different shapes and sizes are best treated together, time being thereby saved. The process is also accelerated by adding some fat oil to the leather shavings, which, of course, must be omitted when, after long use, the shavings have become quite greasy. The drum should be filled about half full, other- wise the articles do not roll freely and polishing is retarded. On the other hand, when the drum is less than half full there is danger of the articles bending, or in case they are hardened, for instance buckles, of breaking. For many purposes polishing in the tumbling drum is of great advantage, since, independent of its cheapness, the sharp edges of the articles are at the same time rounded off. However, with articles the edges of which have to remain sharp, the process cannot be employed. The tumbling drum in which the articles are treated with sand cannot be used for polishing with leather shavings, it be- ing next to impossible to free it entirely from sand. The drums should make from 50 to 70 revolutions per minute; if allowed to revolve more rapidly, the articles take part in the revolutions without rolling together, which, of course, would prevent polishing. The brightening of articles of iron and steel may be simplified by using water to which I per cent, of sulphuric acid has been added. The drum used for the purpose must, of course, be water-tight. By the addition of sand the process is accelerated. 132 ELECTRO-DEPOSITION OF METALS. Nickel and copper blanks for coins are also cleansed in this manner. They are brought into the tumbling drum, together with a pickling fluid, and, when sufficiently treated, are taken out, rinsed, dried in sawdust, and finally stamped. Grinding. For grinding the objects for the electro-plating process, wooden disks covered with leather coated with emery of various degrees of fineness are almost exclusively used. The wooden disks are made of thoroughly seasoned poplar in the manner shown in Fig. 84. The separate pieces are radially glued together, and upon each side in the FlG * 84 ' centre a strengthening piece is glued and secured with screws, so that each segment of the wooden disk is connected with the strengthening piece. The centre of the disk is then provided with a hole corres- ponding to the diameter of the spindle of the grinding lathe, to which it is secured by means of wedges. The periphery as well as the sides is then turned smooth. A good quality of leather previously soaked in water and cut into strips corres- ponding to the width of the wooden disk is then glued to the periphery of the disk, and still further secured by pins of soft wood. When the glue is dry the disk is again wedged upon the spindle and the leather carefully turned ; it is then ready for coating with emery. For this purpose three different kinds of emery are used, a coarse quality (Nos. 60 to 80) for preparatory grinding, a finer quality (No. oo) for fine grinding, and the finest quality (No. oooo) for imparting lustre. The disks thus coated are termed respectively " roughing wheel," " medium wheel," and " fine wheel." With the first the surface of the objects are freed from the rough crust. The coarse-grained emery used for this pur- pose, however, leaves scratches, which have to be removed by grinding upon the medium wheel until the surface of the objects shows only the marks due to the finer quality of emery, which are in their turn removed by the fine wheel. TREATMENT OF METALLIC ARTICLES. 133 In most cases brushing with a circular bristle brush may be substituted for the last grinding, the articles being moistened, with a mixture of oil and emery No. oooo. Care must be had not to execute the brushing, nor the grinding with the finer quality of emery, in the same direction as the preceding grind- ing, but in a right angle to it. Treatment of the grinding disks . The coating of the roughing wheels with emery is effected by applying to them a good qual- ity of glue and rolling them in a dry coarse emery powder. For the medium and fine wheels, however, the emery is mixed with the glue and the mixture applied to the leather. When the first coat is dry, a second is applied, and finally a third. The whole is then thoroughly dried in a warm place. Before use, a piece of tallow is held to the revolving disk for the purpose of impart- ing a certain greasiness to it, and in order to remove any rough- ness due to an unequal application of the emery it is smoothed by pressing a smooth stone against it. While the preparatory grinding upon the roughing wheel is executed dry, i. e., without the use of oil or fat, in fine grinding the objects are frequently moistened with a mixture of oil or tallow and the corresponding No. of emery. When the layer of emery is used up, the re- mainder is soaked with warm water and scraped off with a dull knife. The leather of the disks on which oil or tallow has been used is then thoroughly rubbed with caustic lime or Vienna lime* to remove the greasiness, which would prevent the ad- herence of the layer of glue and emery to be applied later on. When the leather is thoroughly dry a fresh layer of emery may at once be applied. Grinding lathes. For use, the grinding disks or buffs are wedged upon a conical cast-steel spindle provided with a pulley and working in hard-wood bearings, as plainly shown in Fig. 85. The cast-iron standards are screwed to the floor ; the wooden * Vienna lime is prepared from a variety of dolomite which is first burned, then slacked, and finally incinerated for a few hours. It consists of lime and magnesia, and should be kept in well-closed cans, as otherwise it absorbs carbonic acid and moisture from the air, and becomes useless. 134 ELECTRO-DEPOSITION OF METALS. bearings can be shifted forward and backward by wedges and secured in a determined position by a set screw, thus facilitating the removal of the spindle after throwing off the belt. The disks being wedged upon a conical spindle they always run centrically The changing of the disks requires but a few seconds, and on account of the slight friction of the points of the spindle in the wooden bearings the consumption of power is very slight. FIG 85. To avoid the necessity of throwing off the belt while changing the grinding disks, double machines (Fig. 86) are used, the prin- ciple of conical spindles being, however, preserved. The shaft is provided with loose and fast pulley and coupling lever. Grinding is executed by pressing the surfaces to be ground against the face of the disk, moving the objects constantly to and fro. The operation requires a certain manual skill, since, without good reason, no more should be ground away on one place than on another. Special care and skill are required for grinding large round surfaces. TREATMENT OF METALLIC ARTICLES. 135 If the objects are not to be treated with the fine wheel, fine grinding is succeeded by brushing with oil and emery by means of circular brushes formed of bristles set in disks of wood (see Fig. 93 )> Genuine bristles being at -present very expensive, vegetable fibre, so-called fibres, has been successfully substi- tuted for them, the wooden disk being replaced by an iron case, in the bell-shaped cheeks of which the fibre-bundles are secured FIG. 86. by means of strong nuts. Before use it is advisable to saturate the fibre-bundles with oil in order to deprive them of their brittleness, and thus improve their lasting quality. The grinding lathe (Fig. 87) is provided with such a fibre- brush, which can, of course, be just as well placed upon the con- ical spindles of double machines. The iron case is provided with a conical hole corresponding exactly to the conical spindle, the large frictional surface preventing the turning of the brush upon the spindle or its running off. In regard to grinding the various metals, the procedure, according to the hardness of the metal, is as follows : Iron and steel articles are first ground upon the roughing wheel, then fine-ground upon the medium wheel, and finally upon the fine wheel, or brushed with emery with the circular 136 ELECTRO-DEPOSITION OF METALS. brush. Very rough iron surfaces may first be ground upon solid emery wheels before being worked upon the roughing wheel. For depressed surfaces which cannot be reached with the large emery wheels, small walrus- hide wheels coated with glue and emery are placed upon the point of the spindle of the polishing lathe (see Fig. 95). FIG. 87. Brass and copper castings are first ground upon roughing wheels, which have lost part of their sharpness and will no longer attack iron ; they are then ground fine upon the medium wheel, and finally polished upon cloth or felt disks (bobs). (See below, under polishing.} Sheets of brass, German silver, and copper, as furnished by rolling-mills, are only brushed with emery and then polished with Vienna lime or rouge upon bobs. Zinc castings, as, for instance, those produced in lamp fac- tories, are first thoroughly brusjhed by means of circular brushes and emery, and then polished upon cloth bobs. Sheet zinc is only polished with Vienna lime and ail upon cloth bobs secured to the spindle shown in Fig. 95. TREATMENT OF METALLIC ARTICLES. 137 FIG. 88. Polishing. As will be seen from the foregoing, polishing serves for making the articles ready, i. e., the final lustre is im- parted to them upon soft polishing disks with the use of fine polishing powders. The polishing disks or bobs of fine felt, shirting, or cloth, are secured to the polishing lathe, and, accord- ing to the hardness of the metal to be polished, make 2000 to 2500 revolutions per minute. A foot- lathe, such as is shown in Fig. 88, makes generally not over 1800 revo- lutions per minute. Cloth bobs are made by placing pieces of cloth one upon another in the manner described under " Nickeling of sheet zinc," cut- ting out the centre corresponding to the diameter of the spindle, and secur- ing the disks of cloth by means of nuts between two wooden cheeks upon the spindle of the polishing lathe. In place of cloth bobs, solid round disks of felt or wooden disks covered with a layer of felt may be used, especially for polishingsmooth objects without depressions, the fineness and softness of the felt de- pending on the degree of polish to be imparted and the hard- ness of the metal to be manipulated. " Compress" polishing wheels made of leather, felt, canvas, raw hide, walrus, etc., are manufactured by the Hanson & Van Winkle Co., of Newark, N. J. The wheel is shown in Fig 89 and in sectional view in Fig. 90. The body of the wheel is composed of a cast-iron hub and steel side plates riveted to- gether so as to firmly clasp the compress cushion or cover. This cushion is formed of pieces of leather or other material placed on edge across the faoe. of the wheel and held by the shoulders of the steel side plates, which fit grooves turned on the under side of the compressed cushion. This cushion is one or two inches thick, which gives to the wheels elasticity and 138 ELECTRO-DEPOSITION OF METALS. durability. The special qualities and advantages over other wheels claimed for the " compress" wheel by the manufacturers are as folows : 1. Its elastic cushion combined with rigid center. 2. It holds emery better and will run a third longer at one setting up. 3. It will use coarser emery and produce same results. 4. It cuts faster and does more work in the same time. FIG. 89. FIG. 90. J Sectional View. 5. It is more easily kept balanced. 6. It does not endanger life. 7. It has several times the wear of other wheels. 8. The cross grain fiber polishing surface gives a better finish. 9. It pays for itself every thirty days in time and labor saved. The foot-lathe shown in Fig. 91 is designed for light grind- ing, polishing, and buffing, and is especially suited for polishing silver-plate and silver. It is constructed of iron and steel, and made very rigid and strong to prevent vibration. It stands 3 TREATMENT OF METALLIC ARTICLES. 139 FIG. 91. teet 9 inches from floor to centre of spindle, has a 26-inch driving-wheel turned with grooves for three different speeds, and will run the spindle easily at from 300 to 3000 revolutions per minute. The spindle as shown in the illustration is suitable for leather, muslin, and swan's-down bobs, buffs, and mops. This can be unscrewed and replaced by another spindle, which is furnished with a taper screw for the bosses of circular brushes. Double polishing lathes, accord- ing to the American patterns (Figs. 92 and 93), are used for polishing objects of not too large dimensions, while the lathe shown in Fig. 94 serves chiefly for polishing large sheets, the latter being placed upon a smooth wooden support which rests upon the knees of the work- man, as will be described later on in speaking of the nickeling of sheet zinc. Fig. 93 shows a double polishing ing lathe of larger size ; it carries on one side a large felt disk and a small brush, and upon the other a circular brush and a small walrus-hide buff. The spin- dle of the small polishing lathe, Fig. 92, carries a cloth bob. The lathe (Fig. 95) is manufactured by the Hanson & Van Winkle Co., of Newark, N. J. It is shown on a cast-iron pedestal, from which it can be disconnected and placed on a bench, if required. It is made to run at a speed of 3000 revo- lutions per minute, at which speed the most satisfactory results are obtained with muslin buffs, etc. The lathe is made with steel spindles, hard-metal bearings, UNIVERSITY 1 140 ELECTRO-DEPOSITION OF METALS. FIG. 92. FIG. 93. FIG. 94. TREATMENT OF METALLIC ARTICLES. 141 and is designed for quick speeds. By reason of the distribution of metal it runs without vibration. It stands 10 inches high to centre, has spindle 3 feet long, I ^ inches diameter, with collars on both ends of spindle. The pulley is 4 inches in diameter, 3 J^ inches face. The spindle is I inch in diameter between collars. FIG. 95. The lathe is furnished with fast and loose pulleys where re- quired. Detachable taper ends are shown, on which the small- est brush can be run. Polishing rooms are not complete without a good glue pot. The pots used are often home-made affairs, but the steam glue pots shown in Fig. 96 are so superior, and at the same time so low in cost, that it pays every plater to have them. Each pot sits in a separate heater. The heaters are cast-steel chambers through which the steam circulates, keeping the glue at an even heat. These steel chambers also avoid all escaping steam. The heaters are fitted with upright arms to support the wheel 1 4 2 ELECTRO-DEPOSITION OF METALS. while " setting up " with glue. This allows the surplus glue to drop back into the glue pot instead of on the floor. The belt strapping attachment or endless belt machine shown in Fig. 97 is manufactured by the Hanson & Van Winkle Co., of Newark, N. J. The demand for machines of this character FIG. 96. for polishing bicycle parts has greatly increased, and improve- ments have from time to time been made, culminating in the present construction, which is much more solid and the adjust- ment of the tension of the belt can be done without interfering with the operator. There are fewer parts used than in previous machines, and with the flanged wheels that are supplied to go on the pulley lathe, and with the rubber endless belts from I to 3 inches and up to 12 feet in length, makes this machine avail- TREATMENT OF METALLIC ARTICLES. 143 abb for all purposes. It is equally available to manufacturers of criMlery and carriage hardware, and on irregularly shaped articles that cannot be conveniently polished on a circular wheel. No shop is now complete without one or more flexible shafts for grinding, polishing and buffing. In many ways it will be found a profitable and economical device. For cleaning and FIG. 97. grinding heavy castings, for polishing and buffing all metal and glass, it is a most indispensable tool where power is or can be used to advantage. These shafts, Fig. 98, are made in standard sizes, from i^-inch diameter core, suitable for very light work, to i^-inch core, capable of driving a 3-inch drill in iron or steel. Fig. 99 shows the flexible shaft with part of case and core cut away to show the method of construction. The core is built up by laying up or coiling very small tempered steel wires on a small 144 ELECTRO-DEPOSITION OF METALS. FIG. diameter, each successive layer wound in an opposite direction of larger wire, the ends firmly brazed together solid. The fittings are also attached by special brazing. The coil should be well lubricated with animal oil. Never use min- eral oil. Self-acting polishing lathes for sheet-metal will be discussed un- der " Nickeling of zinc sheet." According to the hardness of the material to be polished, ferric oxide (colcothar or rouge), trip- oli, Vienna lime, etc., in the state of an impalpable powder, and generally mixed with oil, or sometimes with alcohol, are used as polishing agents. For hard metals an impalpable rouge of great hardness (No. F of com- merce) is employed, for softer metals a softer rouge (No. F F F), or Vienna lime, tripoli, etc. It is of advantage to melt the rouge with melted wax and a small quantity of tallow, and cast the mixture in moulds with the aid of strong pressure. The sticks thus formed are suffici- ently greasy to render the use of oil superfluous. In order to impregnate the surface of the polishing bob with the polishing material, hold one of the sticks for a second against the revolv- ing disk, and then polish the objects by pressing them against the disk, diligently moving them to and fro. The polishing bob must not be too heavily impregnated with rouge, since a surplus of the latter smears instead of cutting well. In polishing with Vienna lime, it is advisable to moisten the objects to be polished with oil, while the polishing bobs are saturated with the lime by holding a piece of it against them. Another process of polishing, called burnishing, is executed co-cm. TREATMENT OF METALLIC ARTICLES. 145 by means of tools usually made of steel for the first or ground- ing process, or of a very hard stone, such as agate or blood- stone, for finishing. Burnishing is applied to the final polishiug of depositions of the noble metals. FIG. 99. 2. Mechanical treatment during and after the electro-plating process, In this connection, scratch-brushing the depositions will be first considered, the object of this operation being, on the one hand, to promote the regular formation of certain de- posits ; and on the other, to affect the physical properties of the deposits; and, finally, to ascertain whether the deposit ad- heres to the basis-metal. If it is seen by the irregular formation of the deposit that the basis-metal has not been cleaned with sufficient care by the pre- paratory scratch-brushing, the object has to be taken from the bath and the defective places again scratch-brushed with the application of water and sand, or pumice-stone, when the object is again pickled and replaced in the bath. On the other hand, electro-deposited metals are always more or less porous, they having, so to say, a net-like structure, 10 146 ELECTRO-DEPOSITION OF METALS. thougfy it may not be visible to the naked eye. By scratch- brushing the meshes of the net are made closer by particles of metals being forced into them by the brush, and the deposit is thus rendered capable of receiving additional layers of metal. Furthermore, by scratch-brushing the dead deposits acquire a certain lustre which is enhanced by the subsequent polishing process. Finally, by an unsparing application of the scratch- brush, it will best be seen whether the union of the deposit with the basis-metal is sufficiently intimate to stand the subsequent mechanical treatment in polishing without becoming detached. According to the object in view, and the hardness of the de- posit to be manipulated, scratch-brushes of steel or brass wire are chosen. For nickel, which, as a rule, requires scratch- brushing least, and chiefly only for the production of very thick deposits, steel wire of 0.2 millimetre thickness is taken ; for de- posits of copper, brass, and zinc, brass wire of 0.2 millimetre ; for silver, brass wire of 0.15 millimetre; and for gold, brass wire of 0.07 to o.i millimetre. Scratch- brushing is seldom done dry*; the tool as well as the pieces should be constantly kept wet with liquids, especially such as produce a lather in brushing, for instance, water and vinegar, or sour wine, or solutions of cream of tartar or alum, when it is desired to brighten a gold deposit which is too dark ; but that most generally used is a decoction of licorice-root, of horse-chestnut, of marshmallow, of soap- wort, or of the bark of Panama-wood, all of which, being slightly mucilaginous, allow of a gentle scouring with the scratch-brush, with the production of an abundant lather. A good adjunct for scratch-brushing is a shallow wooden tub con- taining the liquid employed, with a board laid across it nearly level with the edges, which, however, project a little above. This board serves as a rest for the pieces. The hand scratch-brush, when operating upon small objects, is held by the workman in the same manner as a paint brush, and is moved over the object with a back and forward motion imparted by the wrist only, the forearm resting on the edge of the tub. For larger objects, the workman holds his extended TREATMENT OF METALLIC ARTICLES. 147 fingers close to the lower part of the scratch brush, so as to give the wires a certain support, and, with raised elbow, 'strikes the pieces repeatedly, at the same time giving the tool a sliding motion. When a hollow is met with, which cannot be scoured longitudinally, a twisting motion is imparted to the tool. FIG. 100. The lathe brush (Fig. TOO) is mounted upon a spindle, and is provided above with a small reservoir to contain the lubricating fluid, a small pipe with a tap serving to conduct the solution from this to a point immediately above the revolving brush. The top of the brush revolves towards the operator, who presents the object to be scratch-brushed to the bottom. The brush is surrounded by a wooden cage or screen to prevent splashing. To protect the operator against the water projected 148 ELECTRO-DEPOSITION OF METALS. by the rapid motion, there is fixed to the top of the frame a small inclined board, which reaches a little lower than the axis of the brush without touching it. This board receives the pro- jected liquid, and lets it fall into a zinc trough, which forms the bottom of the box. Through an outlet provided in one of the angles of the trough a gum tube conveys the waste liquid to a reservoir below. After scratch- brushing every trace of the lubricating liquid must be washed away before placing or re- placing the objects in the bath. The finished electro-plated objects are first rinsed in clean water to remove the solution constituting the bath adhering to them ; they are next immersed in hot water, where they re- main until they have acquired the temperature of the water, and are then quickly rubbed with dry, hot sawdust. It is best to use sawdust of soft wood, free from tannin, such as maple, poplar, or pine ; oak sawdust is not suitable for the purpose on account of its content of tannin, which imparts a dirty color- ation to the electro-deposits. Boxwood sawdust, though much used, is not sufficiently absorbent, and sticks to the moist objects. The sawdust used must be freed from coarser parti- cles of wood by sifting. For holding the sawdust a zinc box with double bottom is frequently used, which is heated by waste steam or some other process. In order to remove all moisture from the pores it is advisable to place plated objects of iron and steel for a few hours in an oven heated to between 140 and 175 F. A very good method of freeing nickeled objects from all moisture which may have collected in the pores is to im- merse them for about ten minutes in boiling linseed oil, and, after allowing them to drain off, to remove the adhering oil by rubbing with sawdust.. According to some electro-platers, the deposit of nickel thus treated loses its brittleness and will stand bending several times, for instance, wire, sheets, etc., without breaking. Experiments made by Dr. George Langbein did not confirm these statements, but the security against rust of the nickeled iron objects is found to be considerably enhanced by boiling in linseed oil. TREATMENT OF METALLIC ARTICLES. 149 The electro-plated objects, when dry, are finely polished, which is effected upon polishing bobs of fine felt, cloth, or flannel, with the use of fine rouge, Vienna lime, tripoli, etc., or by burnishing. Nickel deposits are almost without exception polished upon cloth or felt bobs with rouge or Vienna lime and oil. Copper and brass deposits are polished with fine flannel bobs, the polish- ing powder being applied very sparingly. Deposits of tin are generally only scratch-brushed, it being impossible to impart great lustre to this metal by polishing with bobs : after drying, the deposit is polished with whiting. Deposits of gold and silver as well as of platinum are polished by burnishing, the steel burnisher being used for the grounding process, and an agate or bloodstone burnisher for finishing. The operation of burn- ishing is carried on as follows : Keep the tool continually moistened with soap-suds. Take hold of the tool very near to the end, and lean very hard with it on those parts which are to be burnished, causing it to glide by a backward and forward motion without taking it off the piece. When it is requisite that the hand should pass over a large surface at once without losing its point of support on the work bench, be careful in tak- ing hold of the burnisher to place it just underneath the little finger. By these means the work is done more quickly, and the tool is more solidly fixed in the hand. The burnishers are of various shapes to suit the requirements of different kinds of work, the first rough burnishing being often done by instru- ments with comparatively sharp edges, while the finishing oper- ations are accomplished with rounded ones. Fig. 101 illustrates the most common forms of burnishers of steel and agate. Both must be free from cracks and highly polished. To keep them free from blemishes they are from time to time polished by vigorously rubbing them with fine tin putty, rouge or calcined alum upon a strip of leather fastened upon a piece of wood which is placed in a convenient position upon the work bench. The objects polished with Vienna lime and oil, or with rouge, have to be freed from adhering polishing dirt, which, with flat I5O ELECTRO-DEPOSITION OF METALS. smooth objects, is effected by wiping with a flannel rag and Vienna lime, and in those with depressions or dead surfaces by brushing with a soft brush and soap-water, and then drying in sawdust. FIG. 101. * B. Chemical Treatment. While'the preparation of a pure metallic and, at the same time, smoother surface is the aim of the mechanical treatment, the chemical preparation of the objects serves, on the one hand, the purpose of facilitating the mechanical treatment by soften- ing and dissolving the impure surface, and, on the other, of freeing the mechanically prepared objects from adhering oil, grease, dirt, etc., so as to bring them into the state of absolute purity required for the electro-plating process. Pickling. The composition of the pickling fluid varies according to the nature of the metal which is to be pickled. Cast-iron and wrought-iron objects are pickled in a mixture of TREATMENT OF METALLIC ARTICLES. !$! 1 part by weight of sulphuric acid of 66 Be. and 15 of water; hydrochloric acid may be substituted for the sulphuric acid. An excellent pickle for iron is obtained by mixing 10 quarts of water with 28 ozs. of concentrated sulphuric acid,* dissolving 2 ozs. of zinc in the mixture and adding 12 ozs. of nitric acid. This mixture makes the iron objects bright, while they become black in dilute sulphuric or hydrochloric acid. To cleanse badly rusted iron objects without attacking the iron itself, it is recommended to pickle them in a concentrated solution of chloride of tin, which, however, should not contain too much free acid, as otherwise the iron is attacked. The duration of pickling depends on the more or less thick layer of scale, etc., which is to be removed or softened ; the process may be considerably assisted and the time shortened by frequent scouring with sand or pumice. The pickled articles are rinsed in cold water, then immersed in hot water, and dried in sawdust. In order to neutralize the acid remaining in the pores, it is advisable to make the rinsing water alkaline by the addition of caustic potash or soda, etc. Zinc objects are only pickled when they show a thick layer of oxide, in which case pickling is also effected in dilute sul- phuric or hydrochloric acid, and brushing with fine pumice. A very useful pickle for zinc consists of sulphuric acid 100 parts by weight, nitric acid 100, and common salt I. The zinc objects are immersed in the mixture for one second, and then quickly rinsed off in water which should be frequently changed. Copper, and its alloys brass, bronze, tombac, and German silver, are cleaned and brightened by dipping in a mixture of nitric acid, sulphuric acid, and lampblack, a suitable pickle consisting of sulphuric acid, of 66 Be., 50 parts by weight, nitric acid, of 36 Be., i oo, common salt I, and lampblack I. In order to remove the brown coating, due to cuprous oxide, the objects are first pickled in dilute sulphuric acid, and then dipped for a few seconds, with constant agitation, in the above-mentioned * The acid should be poured into the water, and not the water into the acid. 152 ELECTRO-DEPOSITION OF METALS. pickle until they show a bright appearance. They are then immediately rinsed in water to check any further action of the pickle. If objects of copper or its alloys are not to be subjected, after pickling, to further mechanical treatment, or are to be at once placed in the electro-plating bath, it is best to execute the pick- ling process in two operations by treating them in a preliminary pickle and brightening them in the bright- dipping bath. The preliminary pickle consists of nitric acid, of 36 Be., 200 parts by weight, common salt i, lampblack 2. In this preliminary pickle the articles are allowed to remain until all impurities are removed, when they are rinsed in a large volume of water, dipped in boiling water, so that they quickly dry, and plunged into the bright-dipping bath, which consists of nitric acid, of 40 Be., 75 parts by weight, sulphuric acid, of 60 Be., 100, and common salt I. It is not advisable to bring the objects which have passed through the preliminary pickle and rinsing water directly, while still moist, into the bright-dipping bath, since for the production of a beautiful pure lustre the introduction of water into the bright-dipping bath must be absolutely avoided. Hence the objects treated in the preliminary pickle should first be dried by heating in hot water, shaking the latter off. Potassium cyanide, dissolved in ten times its weight of water, is often used instead of the acid pickle for brass, especially when it is essential that the original polish upon the objects should not be destroyed, as in the preparation of articles for nickel- plating. The objects should remain in this liquid longer than in the acid pickle, because the metallic oxides are far less soluble in this than in the latter. In all cases the final cleaning in water must be observed. All acid pickles used for different kinds of work should be kept distinct from each other, so that one metal may not be dipped into a solution containing a more electro-negative metal, which would deposit upon it by a chemical exchange. The pickled objects must not be unnecessarily exposed to the air, and should be transferred as quickly as possible from the TREATMENT OF METALLIC ARTICLES. 153 pickle to the wash-waters, and then to the electro-plating bath, or, if this is not feasible, kept under pure water. Pickled ob- jects which are not to be plated are carefully washed in water, which should be frequently changed, rinsed, drawn through a solution of tartar, and dried by dipping in hot water and rubbing with saw-dust. Places soldered with soft solder, as well as parts of iron, be- come black by pickling, and have to be brightened by scouring with pumice, or by scratch-brushing. It is frequently required that bright objects of brass or other alloy of copper should be given a dead or dull surface by pick- ling, so that after plating they show a beautiful dead lustre. This may be effected in various ways. Every bright-dipping bath acts as a dead dip if the articles are allowed to remain in it for a longer time and at a higher temperature. A better ef- fect is, however, produced by adding zinc sulphate (white vitriol) to the pickle, the deadening being the stronger the more zinc sulphate is added. A good dead dip is prepared by adding a solution of 0.35 oz. of zinc sulphate in 3^ ozs. of water to the cold mixture of 6j^ Ibs. of nitric acid, of 36 Be., 4.4 Ibs. of sulphuric acid, of 66 Be., and J^ oz. of common salt. According to the shade desired, the articles are left in this mixture for 2 to 10 minutes, and as they come from it with a faded earthy appearance, they are plunged momentarily into a bright-dipping bath, whereby they acquire a dead lustre, and are then quickly rinsed in a large volume of clean water. Generally speaking, it may be said that less depends on the composition of the pickle than on quick and .skillful manipula- tion ; and as good results have always been obtained with the above-mentioned mixture, there is no reason for repeating the innumerable receipts given for pickles. The main points are to have the acid mixture as free from water as possible, further to develop hyponitric acid, which is effected by the reduc- tion of nitric acid in consequence of the addition of organic sub- stances (lampblack, sawdust, etc.), and of chlorine, which is formed by the action of the sulphuric acid upon the common 154 ELECTRO-DEPOSITION OF METALS. salt. The volume of the dipping bath should not be too small, since in pickling the acid mixture becomes heated and the in- creased temperature shows a very rapid, frequently not con- trollable, action, so that a corrosion of small articles may readily take pface. It is therefore necessary to allow the acid mixture, after its preparation, to thoroughly cool off; pour the sulphuric acid into the nitric acid (never the reverse!!}, and allow the mixture, which thereby becomes strongly heated, to cool off to at least the ordinary temperature. In order to be sure of the uniform action of the pickle upon all parts, it is, in all cases, advisable previous to pickling to free the articles from grease by one of the methods given later on. In pickling abundant vapors are evolved which have an in- jurious effect upon the health of the workmen, and corrode metallic articles exposed to them. The operation should, there- fore be conducted in the open air, or under a well-drawing vapor flue. In large establishments it may happen that the quantity of escaping acid vapors is so large as to become a nuisance to the neighborhood, which the proprietors may be ordered by the authorities to abate. The evil is best remedied by a small ab- sorbing plant, as follows: Connect the highest point of the vapor flue D (Fig. 102) by a wide clay pipe R with a brick reservoir, A, laid in cement, so that R enters A a few centimeters above the level of the fluid, kept at the same height by the discharge pipe b. Above, the reservoir is closed by a vault through which the water conduit W is introduced. Below the sieve 5, which is made of wood and coated with lacquer, a wide clay pipe R^ leads to the chimney of the steam boiler ; or the suction pipe of an injector is introduced in this place, in which the air from the vapor flue is sucked through the reservoir and allowed to escape into the open air or into a chimney. Through the man-hole M the sieve-bottom 5 of the reservoir is filled with large pieces of chalk or limestone, the manner of operating being then as follows : A thin jet of water falls upon 5, where it is distributed and runs over the TREATMENT OF METALLIC ARTICLES. 155 layer of chalk. The air of the pickling room saturated with acid vapor moves upward in consequence of the draught of the chimney of the steam boiler, the injector or the ventilator, and yields its content of acid to the layer of chalk, while the neutral solution of calcium nitrate and calcium chloride, which has been formed, runs off through b. FIG. 102. The absorption of the acid vapors may, of course, be effected by apparatus of different construction, but the one above de- scribed may be recommended as being simple, cheap, and effective. The considerable consumption of acid for pickling purposes in large establishments makes it desirable to regain the acid and metal contained in the exhausted dipping baths. The following process has proved very successful for this purpose : Mix the old dipping baths with ^ their volume of concentrated sulphuric acid, and bring the mixture into a nitric acid distill- ing apparatus. Distil the nitric acid off at a moderate temper- ature, condense it in cooled clay-coils, and collect it in glass 156 ELECTRO-DEPOSITION OF METALS. balloons. To the residue in the still add water, precipitate from the blue solution, which contains sulphate of copper and zinc, the copper with zinc waste, and add zinc until evolution of hydrogen no longer takes place. Filter off the precipitated copper through a linen bag, wash and dry. The fluid running off, which contains zinc sulphate, is evaporated to crystallization and yields quite pure zinc sulphate, which may be sold to dye- works, or for the manufacture of zinc-white. According to local conditions, for instance, if the zinc sul- phate cannot be profitably sold in the neighborhood, or zinc waste cannot be obtained, it may be more advantageous to omit the regaining of zinc from the dipping baths. In this case, the fluid which is obtained by mixing the contents of the still with water is compounded with milk of lime until it shows a slightly acid reaction. The gypsum formed is allowed to settle, and after bringing the supernatant clear fluid into another reservoir the copper is precipitated by the introduction of old iron. The first rinsing waters in which the pickled objects are washed are treated in the same manner. The precipitated copper is washed and dried. For the production of a grained surface by pickling a mix- ture of i volume of saturated solution of bichromate of potash in water and 2 volumes of concentrated hydrochloric acid may be recommended. The brass articles are allowed to remain in the mixture for several hours, when they are momentarily plunged into the bright-dipping bath, and rinsed in a large volume of water, which should be frequently changed. Removal of grease. This operation is to be executed with the greatest nicety, because on it chiefly depends the success of electro-plating. Its object is to remove every trace of im- purity, be it due to touching with the hands or to the manipu- lation in grinding and polishing. According to the preparatory treatment of the objects, the removal of grease is a more or less complicated operation. Large amounts of oily or greasy matter should be removed by rinsing in benzine, it being recommended to execute this opera- TREATMENT OF METALLIC ARTICLES. 157 tion immediately after grinding and polishing, so that the oil used in these operations has no chance of hardening as is fre- quently the case with objects polished with Vienna lime and oil. Instead of cleaning with benzine, the objects, as far as their nature allows, may be boiled in a hot lye of I part of caustic potash or soda in 10 of water, until all the grease is saponified, when the dirt, consisting of grinding powder, can be readily re- moved by brushing. In place of solutions of caustic alkalies, hot solutions of potash or soda may be used, but their action is much slower and offers no advantages. Objects of tin, lead, and Britannia, being attacked by the hot lye, must be left in contact with it for a short time only. The articles thus freed from the larger portion of grease are first rinsed in water, and then for the removal of the last traces of grease brushed with a bristle brush and a mixture of water, quick-lime, and whiting, until when rinsing in water all por- tions appear equally moistened and no dry places are visible. The lime mixture is prepared by slaking freshly burnt lime, free from sand, with water to an impalpable powder, mixing i part of this with I of fine whiting, and adding water with constant stirring until a paste of the consistency of syrup is formed. The shape of many objects presents certain difficulties in the removal of grease ; the deeper portions cannot be reached with the brush, as, for instance, in skates, which often are to be nickeled in a finished state. In this case the objects are drawn in succession through three different benzine vessels ; in the first benzine most of the grease is dissolved, the rest in the second, while the third serves for rinsing off. When the ben- zine in the first vessel contains too much grease, it is emptied and filled with fresh benzine, and then serves as the third vessel, while that which was formerly the second becomes the first, and the third the second. After rinsing in the third benzine vessel, the objects are plunged in hot water, then for a few seconds dipped in thin milk of lime, and finally thoroughly rinsed in water. It is recommended not to omit the treatment with milk of lime of objects freed from grease with benzine. I 5 8 ELECTRO-DEPOSITION OF METALS. To avoid subsequent touching with the hands the objects, before freeing them from grease, must of course -be tied to the metallic wires (of soft copper) by which they are suspended in the electro-plating bath. In removing the grease by the wet method a layer of oxide scarcely perceptible to the eye is frequently formed upon the metals. This layer of oxide has to be removed, the liquid used for the purpose varying, of course, with the nature of the layer. Objects of iron and steel as well as of zinc are momentarily plunged in a mixture of sulphuric acid I part by weight and water 20 parts, and quickly rinsed off in clean water. Highly polished objects of iron and steel, after being treated with this mixture, are best again rapidly brushed with lime paste, and, after rinsing off quickly, immediately brought into the electro- plating bath. FIG. 103. Copper p , brass, bronze, German silver, and tombac are best treated with a dilute solution of potassium cyanide, I part of 60 per cent, potassium cyanide in 1 5 to 20 of water. The objects are then quickly rinsed off and placed in the electro-plating bath. Lead and Britannia may be treated with water slightly acidu- lated with nitric acid. The steel spring carboy rocker shown in Fig. 103 overcomes the PROCESSES OF ELECTRO-DEPOSITION. 159 difficult and dangerous operation of tilting heavy carboys con- taining acids. It is the acme of convenience and simplicity. It empties the carboy with ease, saves waste of contents and time in handling, and prevents danger to the person and cloth- ing of the operator. It is very strong, and can be hung up out of the way when not in use. CHAPTER VI. PROCESSES OF ELECTRO-DEPOSITION. NEXT to the proper mechanical and chemical preparations of the objects, the success of the process of electro-deposition de- pends on the suitable composition of the electrolytic solutions (baths), and the current-strength which is conducted into the bath for the precipitation of the metals. In regard to the latter the most essential conditions have already been discussed in Chap. IV., "Electro-plating Plants in General," and will be further referred to in speaking of the several electro-plating processes. Hence, the general rules which have to be observed in the preparation of the baths will first be considered. Water being the solvent for all electrolytic baths, its constitu- tion is by no means of such slight importance as is frequently supposed. Spring and well water often contain considerable quantities of lime, magnesia, common salt, iron, etc., the presence of which may cause various kinds of separations in the baths ; on the other hand, river water is frequently impregnated to such an extent with organic substances that its employment without previous purification cannot be recommended. No doubt, distilled water, or in want of that rain water, is the most suitable for the preparation of baths. However, rain water collected from metal roofs should not be used, nor that running off from other roofs, it being contaminated with dust. Rain water should be l6o ELECTRO-DEPOSITION OF METALS. caught in vessels of glass, earthenware, or wood, free from tannin, and filtered. Where river or well water has to be em- ployed, thorough boiling and filtering before use are abso- lutely necessary in order to separate the carbonates of the alkaline earths held in solution. By boiling, a possible con- tent of sulphuretted hydrogen is also driven off. Another important factor is the purity of the chemicals used for the baths, the premature failure of the latter being in most cases caused by the unsuitable nature of the chemicals, which also frequently gives rise to abnormal phenomena inexplicable to the operator. Chloride of zinc, for instance, may serve as an example. It is found in commerce in very varying quali- ties, it being prepared for dyeing purposes with about 70 per cent, actual content of chloride of zinc, for pharmaceutical pur- poses with about 90 per cent., and for electro-plating purposes with 98 or 99 per cent. Now it will readily be seen that if an operator who is preparing a brass bath according to a formula which calls for pure chloride of zinc uses a preparation in- tended for dyeing purposes, there will be a deficiency of metallic zinc in the bath, and the content of copper in the bath being too large in proportion to the zinc present, will cause reddish shades in the deposits. Likewise, in case the operator uses potassium cyanide of low content, when the formula calls for a pure article with 98 per cent., he will not be able to effect the solution of copper or zinc salts with the quantity prescribed. Furthermore, potassium cyanide, in the preparation of which prussiate of potash containing potassium sulphate is used, will cause, by reason of the formation of potassium sulpho-cyanide, various disturbing influences (formation of bubbles in the deposit), the explanation of which is difficult to the operator, who, trusting to the purity of the chemicals, seeks elsewhere for the causes of the abnormal phenomena. Sodium sulphite may in a similar manner cause great annoy- ance if the suitable preparation is not used. There is a crystal- lized neutral salt which is employed for many gold-baths, and PROCESSES OF ELECTRO-DEPOSITION. l6l also the sodium bisulphite in the form of powder which serves for the preparation of copper and brass baths. If the latter should be used in the preparation of gold baths, the gold would be reduced from the solution of its salts and precipitated as a brown powder. Or, if in preparing nickel baths a salt containing copper is used, the nickeling will never be of a pure white color, but show shades having not even a distant resemblance to the color of nickel. The above-mentioned examples suffice to show how careful the operator must be in the selection of the sources from which he obtains his supplies. It may here be mentioned that all the directions given in the following pages refer to chemically pure products ; where products of a lower standard may be used the content is especially given. For the concentration of the various baths, no general rules can be laid down ; neither can the determination of the density of the baths by the hydrometer be relied on. If the electro- plating solutions consisted of nothing but the pure metallic salts, the specific gravity, which is indicated by the hydrometer- degrees might serve for an estimation of their value. But such an estimation is often apt to prove deceptive, since to decrease the resistance the baths also require conducting salts, and by the addition of a larger quantity of them the specific gravity of a bath may be increased to any extent without the content of the more valuable metal being greater than in a bath showing fewer hydrometer-degrees. If the composition of a correct bath when freshly prepared is known, as well as its gravity in degrees Baume, conclusions as to the condition of the bath may be drawn from changes in the specific gravity. All baths, with the exception of gold baths, measure between 6 and 10 Baume. If now a nickel bath after its preparation shows the standard gravity 7 Be for nickel baths and it shows later on 9, the greater gravity is either due to evaporation of water or to excessive freshening or strengthening of the bath. Such a bath generally yields ii 1 62 ELECTRO-DEPOSITION OF METALS. dark and spotted nickeling, the deposit is formed in a sluggish manner, and the operator may then learn from the hydrometer that the cause of these phenomena is not due to a contamina- tion of the bath, but to its over-concentration. Baths too con- centrated readily deposit salt in crystals on the anodes and on the sides of the vats, which should by no means take placts, and there is even danger that microscopic crystals may deposit upon the articles and cause holes in the deposit. An electrolytic bath should not be poor in metal, as otherwise it soon becomes exhausted, and besides the deposits form more slowly than in a bath with a correct content of metal; on the other hand, the bath must not be too concentrated, as, in this case, salts in the form of crystals readily separate and deposit themselves upon the anodes, the sides of the vessels, and even upon the articles themselves, which may cause holes to form in the deposit ; or the crystals envelop the anodes so tightly that the current cannot reach the bath. Besides, too concentrated baths generally produce discolored deposits, as, for instance, too concentrated nickel baths, which yield a dark and spotted deposit. Hence in summer, when the bath has a higher temperature, it may be made more concentrated than in winter. If crystals are separated out, even when the bath shows a temperature of 58 F., it must be diluted with water until the formation of crys- tals ceases, after those which have been formed have been dis- solved in hot water added to the bath. In order that all strata of the bath may show an equal con- tent of metal, it is advisable in the evening, after the day's work is done, to thoroughly stir up the solution with a wooden crutch. For practical reasons the baths are generally made one-quarter to one-third deeper than corresponds to the lengths of the ob- jects to be plated. In consequence of this, the strata of fluid between the anodes and the objects become poorer in metal than those on the bottom, and the object of stirring up is to re- store the same concentration to all portions of the bath. The strata of fluid which come in contact with the anodes be- UNIVERSITY PROCESSES OF ELECTRO-DEPOSITION. 163 FIG. 104. come, by the absorption of metal, specifically heavier than the other strata, and sink to the bottom ; on the other hand, the strata of fluid which yield metal to the objects become specifi- cally lighter and rise to the top. A partial compensation of course takes place by diffusion, but not a complete one, and from this cause arise several evils. The heavier and more satu- rated fluid offering greater resistance to the current, the anodes are attacked chiefly on the upper portions where the specifically lighter layer of fluid is ; practically this is proved by the appearance of the anodes which, at first square, after being for some time used assume the shape shown in Fig. 104. On the other hand, the portions of the cathodes (objects) which come in contact, near the surface, with strata of fluid poorer in metal, acquire a deposit of less thickness than the lower portions which dip into the bath where it is richer in metal. Now, if the bath also contains free acid, and if there is a con- siderable difference in the specific gravity of the lower and upper strata of fluid, the electrode, which touches both strata, produces a current, the effect of which is that metal dissolves from the upper portions and deposits upon the lower. This explains the phenomenon that a deposit on the upper portions of the objects may be redissolved, even when a current, which, however, must be very weak, is conducted into the bath from an external source. Many authors, therefore, go so far as to demand that during the electro-plating process the baths should be kept in con- stant agitation by mechanical means. This, however, is scarcely necessary, because a homogeneity of the solution is to a certain extent effected by the agitation of the fluid in suspending and taking out the objects. Hence as long as objects are put in and taken out an agitation naturally takes place in which all the strata of fluid between the objects and anodes take part, while only the deepest strata, which do not come into contact with the objects and the anodes, remain in a state of stagnation. 1 64 ELECTRO-DEPOSITION OF METALS. Constant agitation of the electro-plating solution is of ad- vantage only in silvering and in the galvano-plastic reproduc- tion in the acid copper bath, in which the objects have to remain four to five and eight to ten hours. Some authors de- mand constant agitation for the more rapid removal of the bubbles of hydrogen which form on the objects ; but the same end is attained without complicated contrivances, by the operator accustoming himself to strike the object-rod a slight blow with the finger each time he suspends an object. The degree of temperature required for the electro-plating solutions has already been discussed on page 86, where also the means have been given by which too cool solutions may be brought to the proper degree of temperature. Baths which are to be used cold should under no circumstances show a temperature below 59 F., it being best to maintain them at between 64.5 and and 68 F. Boiling is required in the preparation of many baths, if, FIG. 105. FIG. 106. after cooling, they are to yield good and certain results. The kettles and boiling-pans used for the purpose are of various shapes, hemispherical or with flat bottom, and are made of different materials (Figs. 105 and 106), those of enameled iron, or, for small baths, of porcelain or earthenware, being best. The enamel of the iron kettles must be of a composi- tion which is not attacked by the bath. Notwithstanding their enamel these vessels become gradually impregnated with the solutions they have held, and it is dangerous to employ them for different kinds of baths. Thus, an enameled kettle which has been used for silvering will not be suitable, even after the PROCESSES OF ELECTRO-DEPOSITION. 1 65 most thorough washing, for a gold bath, as the gilding will certainly be white or green, according to the quantity of silver retained by the vessel. The use of metal vessels should be avoided ; copper and brass baths may, however, be boiled in strong copper kettles, though they are somewhat attacked. A copper kettle, after being freed from grease and scoured bright, may be provided with a thick deposit of nickel, by fill- ing it with a nickel bath, connecting it with the negative pole of a strong battery or dynamo machine, and suspending in it a number of nickel anodes connected with the positive pole. Such nickeled kettle may be used for boiling nickel baths, but enameled kettles or large dishes of nickel-sheet deserve the preference. If the boiling of large quantities of fluid is not convenient, the same end may be attained by thoroughly working the bath for a few days with the electric current. Suspend to the anode- rods as many anodes as possible, secure to the object-rods a few plates of the same metal, and introduce a current of medium strength, until an object, from time to lime, suspended in the bath acquires a regular deposit. This method is frequently and very successfully used for large brass baths. Nickel baths as a rule do not require actual boiling, but the nickel and certain conducting salts which together form the nickel bath dissolve with difficulty in cold water, and for this reason solution is effected in hot water. If for the preparation of nickel baths, nickel salts dissolving with difficulty have to be dissolved with the assistance of heat and a suitable kettle is wanting, the following procedure may be adopted : Bring water in a clean, bright copper kettle to the boiling point, pour the hot water into a clean wooden bucket having a capacity of 8 to 10 quarts, introduce the amount of nickel salt corresponding to this quantity of water, and stir wiUi a piece of wood until solution is complete. However, with large baths this process would require too much time, and it is, therefore, better to have a large oval or round wooden vat lined with pure sheet lead and provided with 1 66 ELECTRO-DEPOSITION OF METALS. a lead coil for the introduction of steam by means of which the contents of the vat are brought to the boiling-point. If the prepared and boiled solutions are not entirely clear, they have to be filtered, which for large baths is best effected with bags of fine felt ; and for smaller baths, especially those of the noble metals, with filtering paper. To secure lasting qualities to the baths, they must be care- fully protected from every possible contamination. When not in use for plating they should be covered to keep out dust. The objects before being placed in the baths should be free from adhering scouring material or dipping fluid, which other- wise might, in time, spoil the bath. The cleansing of the anode and object rods by means of sand-paper, or emery-paper, should never be done over the bath, so as to avoid the danger of the latter being contaminated by the oxides of the metal constituting the rods falling into it. When a visible layer of dust has collected upon the bath, it must be removed, as other- wise particles of dust might deposit upon the articles and pre- vent an intimate union of the deposit with the basis-metal. With large baths the removal of the layer of dust is readily effected by drawing a large piece of filtering or tissue paper over the surface, and repeating the operation with fresh sheets of clean paper until all the dust is removed. Small baths should be filtered. The choice of anodes is also an important factor for keeping the baths in good condition, as well as for obtaining good results. The anodes should always consist of the metal which is deposited from the solution ; and the metal used for them must be pzire and free from all admixtures. To replace as much as possible the metal withdrawn from the bath by the electro-plating process, the anodes must be soluble ; and it is wrong if, for instance, nickel baths are charged with insoluble anodes of carbon ; or for smaller baths, of sheet platinum. Such insoluble anodes cause a steady and rapid declination in the content of metal, an excessive formation of acid in the bath, and, by the detachment of particles of carbon, a contamination PROCESSES OF ELECTRO-DEPOSITION. 167 of the solution. Further particulars in regard to anodes will be given in discussing the separate baths. When upon a pure metallic surface another metal is electro- deposited, the first portion of the deposit penetrates into the basis-metal, thus forming an alloy. This may be readily proved by repeating Gore's experiments : If a thick layer of copper be precipitated upon a platinum sheet, and then heated to a dark red heat, the deposit can be entirely peeled off; by then heat- ing the platinum sheet with nitric acid, and thoroughly wash- ing with water, it appears, after drying, entirely white and pure. By re-heating the sheet, the surface becomes again blackened by cupric oxide, and by frequently repeating the same opera- tion a fresh film of cupric oxide will always be obtained. This penetration of the deposit into the basis-metal, however, does not merely take place during electro-plating, but also later on ; and it may frequently be observed that, for instance, zinc objects only slightly coppered or brassed, after some time be- come again white. Since this also happens when the deposits are protected by a coat of lacquer against atmospheric influ- ences, the only explanation of the phenomenon can be that the deposit is absorbed by the basis-metal, which is also confirmed by analysis. This fact must be taken into consideration if dur- able deposits are to be produced. To guarantee good performance an electro-plating bath must fulfil the following conditions: 1. It must possess good working capacity. 2. It must exert a sufficiently dissolving action upon the anode. 3. It must reduce the metal in abundance and in a reguline state. . 4. It must not be chemically decomposed by the metals to be plated, hence not by simple immersion ; the adher- ence of the deposit to the basis-metal being in this case impaired. 5. It must not be essentially decomposed by air and light. 1 68 ELECTRO-DEPOSITION OF MEl'ALS. Reduction of metals without a battery (electro-deposition by contact) . We may here appropriately mention the reduction of metals which takes place by the contact of two metals in one fluid without the aid of an exterior source of current. That an electric cur- rent is thereby generated has been previously explained : one metal, by coming in contact with a more electro-positive one, becomes electro-negative and decomposes the fluid. If the latter is a metallic solution, and the metal contained in it not more strongly electro-negative than the negatively excited metal, a separation of metal takes place in consequence of decomposi- tion. This process is termed electro- deposition by contact. Gen- erally the metals which are to be coated are brought in contact with a bright rod of zinc, the latter being a highly electro- positive metal. The zinc is allowed to dip in only so far as to secure a sure contact with the metal to be coated. The contact of one metal with two fluids or that of two metals in two fluids, presents similar phenomena, an electric current with visible action manifesting itself, and in the latter case we have a complete element. By dipping the more electro-negative metal in a metallic solution whose metal is not more electro-negative, the metal separates from the solution upon the metallic strip dipping in. While by the contact of one metal with another in one fluid, only thin deposits can be produced, and by coating the electro-negative metal with the separated metal, the contact-current loses some of its original strength, by immersing two metals in two fluids, deposits of considerable thickness can under certain conditions be pro- duced, as, for instance, with the galvano-plastic cell apparatus, which will be discussed later on. A reduction of metal can also be brought about by dipping one metal into one fluid. This may take place in consequence of the simple solution of the metal dipped in, and hence the separation may be conceived as a simple chemical action. In how far electric currents manifest themselves and co-operate thereby is still undecided. It is only known that the electro- DEPOSITION OF NICKEL AND COBALT. 169 positive metals, such as zinc, tin, iron, copper, can reduce the electro- negative metals, such as mercury, silver, gold, etc., from the solutions of their salts, and that the reduction is the more rapid and the stronger the more electro-positive the metal dipped in is, and the more electro-negative the dissolved metal is. Upon this action is based coppering, silvering, gilding, etc., by immersion. CHAPTER VII. DEPOSITION OF NICKEL AND COBALT. i. NICKELING. ALTHOUGH nickel-plating is of comparatively recent origin, it shall be first described, since chiefly by reason of the devel- opment of the dynamo-electrical machine it has steadily grown in popularity and become an industry of great magnitude and importance. The great popularity which nickel-plating enjoys is due to the excellent .properties of the nickel itself; the almost silvery whiteness of the metal, its cheapness as com- pared with silver, and the hardness of the electro-deposited metal, which give the coating great power to resist wear and abrasion ; its capability of taking a high polish ; the fact that it is not blackened by the action of sulphurous vapors which rapidly tarnish silver, and finally the fact that it exhibits but little tendency to oxidize even in the presence of moisture. Properties of nickel. Pure nickel is a lustrous, silvery white metal with a slight steel-gray tinge. It is hard, malleable and ductile. Its specific gravity varies from 8.3 (cast nickel plates) to 9.3 (wrought or rolled plates). It melts at about the same temperature as iron, but is more fusible when combined with carbon. It is slightly magnetic at ordinary temperatures, but loses this property on heating to 680 F. I/O ELECTRO-DEPOSITION OF METALS. The metal is soluble in dilute nitric acid, concentrated nitric acid rendering it passive, i. e., insoluble. In hydrochloric and sulphuric acids it dissolves very slowly, especially when in a compact state. Certain articles, for instance hot fats, strongly attack nickel, while vinegar, beer, mustard, tea, and other infusions produce stains ; hence, the nickeling of culinary utensils or the use of nickel-plated sheet-iron for culinary utensils cannot be recom- mended. The chemical equivalent of nickel is 29.5. Nickel baths. The first requisite in preparing nickel baths is the use of absolutely pure chemicals, and in choosing the nickel salts to be especially careful that they are free from salts of iron, copper, and other metals. Furthermore, it is not indifferent what kind of nickel salt is used, whether nickel chloride, nickel sulphate, the double sulphate of nickel and ammonium, etc., but the choice of the salt depends chiefly on the nature of the metal which is to be nickeled. There are a large number of general directions for nickel baths, of which nickel chloride, ammonio- nickel chloride, nickel nitrate, etc., form the active constituents, and yet it would be a grave mistake to use these salts for nickel- ing iron, because the liberated acid, if not immediately and completely fixed by the anodes in dissolving, imparts to the iron objects a great tendency to the formation of rust. Iron objects nickelled in such a bath, to be sure, come out faultless, but in a short time, even if stored in a dry place, portions of the nickel layer will be observed to peel off, and by closely examining such objects it will be seen that under the deposit of nickel a layer of rust has formed which actually tears the nickel off. The use of nickel sulphates or of the salts with organic acids is, therefore, considered best. It might be objected that the liberated sulphuric acid produces in like manner a formation of rust upon the iron objects ; but according to long experience and many thorough examinations such is not the case, the tendency to the formation of rust being only imparted by the use of the chloride and nitrate. The use of nickel salts with DEPOSITION OF NICKEL AND COBALT. I /I organic acids is in many cases more advantageous than that of the sulphates, but such salts are considerably dearer, and hence they are less frequently employed; in many prepared nickeling salts they form the active constituent. The composition of the conducting salts requires the same deliberation as that of the nickeling salts. To decrease the resistance of the nickel solu- tions, conducting salts are added to them, which are also partially decomposed by the current. Like the use of nickel chloride in nickeling iron, an addition of ammonium chloride, which is much liked, cannot be recommended, though the sub- sequent easy reduction of nickel invites its employment. For copper and its alloys, zinc, etc., the chlorine combina- tions may be used, but for nickeling iron they must be avoided as the source of future evils. The use of sodium sulphide, sodium nitrate, barium oxalate, ammonium nitrate, sodium sul- phate, and ammonia-alum as conducting salts, which has been recommended by various authors, is unsuitable. With few exceptions, which will be given later on, the best basis for the conducting salt, according to Bottger and Adams, is am- monia, especially in the form of ammonium sulphate or hydro- chlorate, provided the latter is not used for baths for nickeling iron. Some other additions to the nickeling bath which are claimed to effect a pure silvery-white reduction of the nickel have been recommended by various experts. Thus, the presence of small quantities of an organic acid has been proposed ; for instance, boric acid by Weston, benzoic acid by Powell, and citric acid or acetic acid by others. The presence of small quantities of a free acid effects without doubt the reduction of a whiter nickel than is the case with a neutral or alkaline solution. Hence a slightly acid reaction of the nickeling bath, due to the presence of citric acid, etc., with the exclusion of the strong acids of the metalloids, can be highly recommended. The quantity of free acid must, however, not be too large, as this would cause the deposit to peel off. Boric acidy recommended by Weston as an addition to nickel- ELECTRO- DEPOSITION OF METALS. ing and all other baths, has a favorable effect upon the pure white reduction of the nickel, especially in nickeling rough castings, i. e., surfaces not ground. Weston claims that boric acid prevents the formation of basic nickel combinations on the objects, and that it makes the deposit of nickel more adherent, softer, and more flexible. Whether with a correct current- strength, basic nickel salts, to which the yellowish tone of the nickeling is said to be due, are separated on the cathode, is not yet proved, and would seem more than doubtful. The action of the boric acid has not yet been scientifically explained, but numerous experiments have shown that the deposition of nickel from nickel solution containing boric acid is neither more ad- herent nor softer and more flexible than that from a solution containing small quantities of a free organic acid. Just the contrary, the deposition is harder and more brittle in the pres- ence of boric acid, and different results may very likely be due to the employment of currents of varying strength. A weak current always and under all conditions causes the deposition of a harder and more brittle nickel than a current of medium strength; and in order to judge the quality of the deposited nickel from baths of varying composition, the surface of the objects and of the anodes must always be the same, and cur- rents of equal quantity and electro-motive force be conducted into the bath. Weston's bath will be spoken of later on. Powell's proposition for the use of benzoic acid need scarcely be taken seriously, since the results from baths containing it differ in. no respect from those without it. Before giving suitable formulae for the composition of nickel baths, it will be necessary to discuss the means of determining their acidity and alkalinity. As previously mentioned, a nickel bath, to yield a beautiful white deposit, should contain only a small quantity of free acid ; too much acid preventing the firm adherence of the deposit, while alkaline and even neutral baths do not yield nickel of a pure white color, but of a somewhat darker tone. A bath is neutral when it contains neither free acid nor free alkali, which is recognized by neither blue nor red DEPOSITION OF NICKEL AND COBALT. 1/3 litmus-paper* being changed by the solution. Blue litmus- paper is colored red by acid fluids, and red litmus-paper blue by alkaline fluids. By simultaneously dipping one-half of a strip of blue and of red litmus-paper in the solution, the re- action of the fluid can be judged from the change in color and the rapidity and intensity of its appearance. If a bath which, like most nickel baths, is to work with only a slight reaction, immediately and intensely reddens blue litmus-paper, a suitable alkali has to be added until the coloration of a fresh strip of litmus-paper appears slower and less intense. If, on the other hand, the test shows that red litmus-paper becomes blue, and that consequently the bath is alkaline, a slight acid reaction is restored by the gradual addition of citric acid or another acid suitable to the composition of the bath. Baths made with boric acid form an exception, and must work with a strong acid reaction. I. The most simple nickel bath consists of a solution of 8 to 10 parts by weight of pure nickel ammonium sulphate in 100 parts by weight of distilled water. If too acid, the solution is neutralized with spirits of sal ammoniac to a slightly acid re- action. The solution is prepared by boiling the salt with the corresponding quantity of water, using in summer 10 parts of nickel salt to 100 of water, but in winter only 8 parts, to pre- vent the nickel salt from crystallizing out. This bath, which is frequently used, possesses, however, a considerable degree of resistance to conduction, and hence requires a strong cur- rent for the deposition of the nickel. It also requires cast nickel anodes, since with the use of rolled anodes nickeling proceeds in a very sluggish manner. However, the cast anodes rapidly render the bath alkaline, necessitating a frequent cor- rection of the reaction. To decrease the resistance, recourse has been had to certain conducting salts, and, below, the more common nickel baths will be discussed, together with their mode of preparation and action, as well as their availability for certain purposes. * Blue and red litmus-paper must be kept, each by itself, in well-closed glass jars. 174 ELECTRO-DEPOSITION OF METALS. II. Nickel ammonium sulphate 17 ozs., ammonium sulphate 17 ozs., distilled water 10 quarts. Boil the salts with the water, and, if the solution is too acid, restore its neutrality by spirits of sal ammoniac ; then grad- ually add solution of citric acid until blue litmus-paper is slowly but visibly reddened. The bath deposits rapidly, it possessing but little resistance; an electro-motive force of 1.8 to 2 volts suffices, and all metals (zinc, lead, tin, and Britannia, after previous coppering) can be nickeled in this bath. How- ever, upon rough castings and iron a pure white deposit is difficult to obtain, frequent scratch-brushing with a medium hard steel brush being required. On account of the great content of sulphate of ammonium in the bath, the nickel de- posit piles up especially on the lower portions of the objects, which, in consequence, readily become dull (burn or over- nickel, for which see later on), while the upper portions are not sufficiently nickeled. For this reason the objects must be frequently turned in the bath so that the lower portions come uppermost. This piling up of the deposit also frequently pre- vents the latter from acquiring a uniform thickness. III. Nickel ammonium sulphate 25}^ ozs., ammonium sul- phate 8 ozs., crystallized citric acid i$ ozs., water 10 to 12 quarts. This bath is prepared in the same manner as the preceding, the salts being dissolved in boiling water, and ammonia added until blue litmus-paper is only slightly reddened. This bath requires a somewhat greater electro-motive force than the preceding, or about 2 to 2.2 volts. The formation of the nickel deposit is, however, more uniform, of a beautiful white color, dense and hard, and consequently bears polishing without danger of the nickel grinding off, even if not very thickly plated. It is very suitable for nickeling ground surgi- cal instruments, as well as all ground iron articles which are to be thickly and solidly plated, and for heavy, solid nickeling of copper, brass, bronze, etc. It is much used in this country, either with or without the addition of citric acid. DEPOSITION OF NICKEL AND COBALT. 175 If, after working for some time, the bath loses conducting power, the objects, with the use of the proper current, become blackish without a reduction of nickel being perceptible; while with a stronger current the objects are nickeled white, but the deposit readily peels off. In this case the conducting power has to be increased by the addition of ammonium sulphate. The bath should always be kept so that it shows a slightly acid reaction. It is best to use rolled anodes. IV. Nickel ammonium sulphate 23 ozs., ammonium chloride (crystallized) 11^2 ozs., water 10 to 12 quarts. The bath is prepared in the same manner as given for II. and III. It nickels very rapidly and quite white, but the de- posit is soft, and hence care must be had in polishing upon cloth or felt bobs, the corners and edges of the objects espec- ially requiring careful handling. On account of the danger of peeling off, a heavy deposit of nickel cannot be obtained in this bath, since, in consequence of the rapid precipitation, the de- posit condenses and absorbs hydrogen, is formed with a coarser structure, and turns out less uniform and dense. These phe- nomena are a hindrance to a heavy deposit, which, if it is to adhere, must be homogeneous and dense. As previously men- tioned, baths with the addition of chlorides as well as those pre- pared with nickel chloride and nickel nitrate are not suitable for the solid nickeling of iron ; they are, however, well adapted to the rapid light nickeling of cheap brass articles. The electro- motive force required for this bath is 1.8 volts. V. Nickel chloride (crystallized) 17^ ozs., ammonium chlor- ide (crystallized) 17^ ozs., water 12 to 15 quarts. The bath is prepared in the same manner as given for II. and III., though solution may be effected cold. The bath precipi- tates very readily, and is especially liked for nickeling zinc cast- ings. Tension of current, 1.5 to 1.75 volts. For nickeling iron this bath has the same disadvantages, and even to a still greater extent than the preceding. VI. Baths containing boric acid. Weston recommends the following composition for nickel baths: Nickel chloride 1/6 ELECTRO-DEPOSITION OF METALS. ozs., boric acid 7 ozs., water 20 quarts ; or, nickel-ammonium sulphate 35 ozs., boric acid 17 j ozs., water 25 to 30 quarts. Both solutions are said to be improved by adding caustic potash or caustic soda so long as the precipitate formed by the addition dissolves.* These compositions, however, cannot be recommended, chiefly because the baths work faultlessly for a comparatively short time only; all kinds of disturbing phenomena make their appearance, the deposit being no longer white but blackish, and the baths soon failing entirely. Kaselowsky's formula yields similar results. It is prepared by dissolving, with the assistance of heat, 35%! ozs. of nickel-ammonium sulphate and i/3/^ ozs. of boric acid in 20 quarts of water. If an entirely neutral double sulphate has not been employed, this bath also generally fails after two or three months' use. The cause of this has to be primarily sought in the fact that baths prepared with boric acid require according to their composition a definite proportion between the rolled and cast nickel anodes present in the bath. If rolled anodes are exclusively used, free sulphuric acid is soon formed, which causes energetic evolution of hydrogen on the articles, but prevents a vigorous deposit and imparts to the latter a tendency to peel off. The same thing happens when a nickel salt not entirely neutral has been used in the prepara- tion of the bath. If, on the other hand, cast nickel anodes alone are employed, the bath soon becomes alkaline, with turbidity and the formation of slime, and the deposit turns out gray and dull before it possesses sufficient thickness. From the foregoing it will be readily understood that the nickel salt used must be neutral and that the proportion of rolled to cast anodes must be so chosen that the free sul- phuric acid formed on the cast anodes is neutralized, but that the acidity of the bath dependent on the free boric acid is con- stantly maintained. Such a bath containing boric acid may advantageously be prepared as follows: * Dingler's Journal, 235, p. 404. Wagner's Jahresbericht, 1883, p. 146. DEPOSITION OF NICKEL AND COBALT. VII. Nickel-ammonium sulphate 21 ozs., chemically pure nickel carbonate I ^ ozs., chemically pure boric acid (crys- tallized) 10^ ozs., water 10 to 12 quarts. Boil the nickel-ammonium sulphate and the nickel carbonate in the water until the evolution of bubbles of carbonic acid ceases and blue litmus paper is no longer reddened. After allowing sufficient time for settling, decant the solution from any undissolved nickel carbonate and add the boric acid. Boil the whole a few minutes longer, and allow to cool. If the nickel salt contains no free acid, boiling with the nickel car- bonate may be omitted. The solution shows a strongly acid reaction which must not be removed by alkaline additions. The proportion of cast to rolled anodes used in this bath is dependent on the quality of the anodes. The use of readily soluble cast anodes requires the suspension in the bath of more rolled anodes than when cast anodes dissolving with difficulty are employed, since the latter in consequence of rapid cooling have a surface not readily attacked. The pro- portion has likewise to be changed, with the use of soft or hard-rolled anodes. Hence the proper proportion will have to be established by frequently testing the reaction of the bath. For testing the bath the following rules may be laid down: Blue litmus-paper must always be perceptibly and in- tensely reddened, but congo-paper should not change its red color, for if the latter turns blue it is an indication of the pres- ence 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 cannot be recommended for neutral- izing free sulphuric acid in this bath. Red litmus-paper must remain red, 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. The bath prepared according to the above formula (VII) requires an electro-motive force of about 2.3 to 2.5 volts. 12 178 ELECTRO-DEPOSITION OF METALS. Below are given a few other formulae for nickel baths which may be advantageously used for special purposes, but not for equally good nickeling of all kinds of metals. VIII. Nickel sulphate lo^J ozs., potassium citrate 7 ozs., ammonium chloride 7 ozs., water 10 to 12 quarts. To prepare the bath dissolve 10^ ounces of nickel sulphate and ^y 2 ounces of pure crystallized citric acid in 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. The 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 nickeling of zinc articles; it must, however, be kept strictly neutral. The bath works with rolled anodes, and but seldom requires a correction of the reaction. IX. Nickel phosphate 8^ ozs., sodium pyrophosphate 26^ ozs., water 10 to 15 quarts. Dissolve the sodium pyrophos- phate in water, heat the solution to about 167 F. and add the nickel phosphate with constant stirring. Nickel phosphate is obtained as a pale green powder by precipitating solution of nickel sulphate with sodium phosphate. This bath yields a very fine dark nickeling upon iron, brass, and copper, as well as directly \ without previous coppering, upon sheet zinc and zinc castings, and may be advantageously used for decorative purposes where darker tones of nickel are de- manded. X. A fairly good nickel-bath for electro-platers having but a feeble current at their disposal is obtained from a solution of nickel-ammonium sulphate 22 J^ ozs., magnesium sulphate iij^ ozs., water 10 to 12 quarts. This bath precipitates readily and strongly, and a heavy coating can also be deposited upon iron without fear of the DEPOSITION OF NICKEL AND COBALT. 179 disagreeable consequences of bath IV. ; even zinc may be directly nickeled in it with a comparatively feeble current. The deposit, however, turns out rather soft, with a yellowish tinge, and the bath does not remain constant, but fails after working at the utmost three or four months, the anodes being scarcely attacked. Below are given the compositions of a few nickel baths which have been highly recommended: XL Pure nickel sulphate 35 J^ ozs., neutral ammonium tar- trate 26^ ozs., tannin 77 grains, water 20 quarts. Neutral ammonium tartrate is obtained by saturating a solution of tar- taric acid with ammonia. The nickel salt must also be neutral. For this purpose dissolve the above-mentioned ingredients in 3 or 4 quarts of water and boil the solution for l / hour, then add enough water to make 20 quarts of fluid, and filter. The bath is said to yield a very white, soft, and homogeneous deposit of any desired thickness, without roughness or danger of peeling off. On rough or polished castings thick deposits may be ob- tained at a cost scarcely exceeding that of coppering. Galvano- plastic reproduction may also be effected in this bath. For those who wish to try the bath it may be mentioned that the most suitable current-strength is 3.5 volts. XII. An English formula is as follows: Dissolve 17^ ozs. of nickel sulphate, 9^ ozs. of tartaric acid, and 2j ozs. of caustic potash in 10 quarts of water. The addition of bisulphide of carbon to nickel baths, which has been recommended by Bruce, is not advisable. Ac- cording to Bruce, such an addition prevents the nickel de- posits from becoming dull when reaching a certain thickness, but repeated experiments made strictly in accordance with the directions given did not confirm this statement. XIII. For nickeling small articles the following bath is claimed to yield excellent results : Nickel-ammonium sulphate 64 ozs., ammonium sulphate 20^ ozs., crystallized citric acid ozs. For the production of very thick deposits, the following has 180 ELECTRO-DEPOSITION OF METALS. been recommended: Nickel ammonium sulphate 16 ozs., sodium citrate 10 ozs., water 10 quartos. This bath is said to be especially useful in preparing nickel cliches. However, numerous experiences proved it to possess the disadvantages of all nickel baths prepared with large quantities of organic combinations, and for the special purpose for which it is re- commended no better results were obtained than with any other nickel bath rationally composed for heavy deposits. In some works on galvanoplasty a solution of nickel cyanide in potassium cyanide is recommended for nickeling, but ex- periments failed to obtain a proper reduction of nickel. We would here add the general remark that fres/tfy prepared nickel baths mostly work correctly from the beginning, though it may sometimes happen that the articles first nickeled come from the bath with a somewhat darker tone. In such case it is advisable to suspend a few anodes to the cathode and allow the bath to work one or two hours, when the nickeling will proceed faultlessly. A few words may here be said in regard to what may be termed a nickel bath without nickel salt. It simply consists of a 15 to 20 per cent, solution of ammonium chloride, which trans- fers the nickel from the anodes to the articles. Cast anodes are almost exclusively used for the purpose, and deposition may be effected with quite a feeble current. Before the solution ac- quires the capacity of depositing, quite a strong current has to be conducted through the bath until the commencement of a proper reduction of nickel. This bath is only suitable for coloring very cheap articles, it not being possible to produce solid nickeling with it ; and 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 sal ammoniac solution without the use of metallic salts, for in- stance, iron, zinc, cobalt, etc. Nickel anodes. Either cast or rolled nickel plates are used as anodes, which must of course be as pure as it is possible to ob- tain them. Every impurity of the anodes passes into the bath DEPOSITION OF NICKEL AND COBALT. l8l and jeopardizes its successful working. If too thin the anodes increase the resistance ; for small baths rolled anodes 0.079 inch thick are generally used, and as a rule they should not be less than 0.039 mcn thick. For larger baths it is better to use plates from o.n to 0.19 inch thick, while the thickness of cast anodes may vary between o.n and 0.39 inch, according to the size of the bath and the purpose for which it is to be used. The use of insoluble anodes of gas-carbon or platinum, either by themselves or in conjunction with nickel anodes, as fre- quently recommended, 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 fulfils 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 seems that the possibility of a bath also becoming alkaline even with the sole use of rolled anodes, especially when working with a strong current, has led to the proposal of suspending in the bath, be- sides the nickel anodes, a sufficient number of insoluble anodes in order to effect a constant neutrality of the bath. It would lead too far to go into the theory of the secondary decomposi- tions 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 proposal shall here be overthrown by practical reasons, it only requiring to be demonstrated 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 me- tallic content should not be accelerated by the use of insoluble anodes. For larger baths the use of expensive platinum 1 82 ELECTRO-DEPOSITION OF METALS. anodes as insoluble anodes need not be taken into considera- tion, because for large surfaces of objects correspondingly large surfaces 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 case, because, though the platinum does absolutely not dissolve, 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 becoming constantly detached, and floating upon the bath, deposit themselves upon the ob- jects 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 in- equality in the thickness of the deposit is again a hindrance to obtaining layers of good and uniform thickness, such as are required for solid nickeling. Since the current preferably seeks its compensation through these 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 carbon becom- ing detached, the latter being thus prevented from depositing upon the articles in the bath. DEPOSITION OF NICKEL AND COBALT. 183 According to long practical experience, the best plan is to use rolled and cast anodes together in one bath. The propor- tion of cast to rolled anodes depends on the composition 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 re- sistance more rolled anodes. Cast anodes, to be sure, have the disadvantage of soon becoming spongy, and crumbling before being entirely used up. Furthermore, the surfaces of nickel anodes cast in iron moulds are so hard as to temporarily resist the action of the bath, while the interior dissolves only partially, since, on the one hand, the oxygen separating on the anode, which is necessary for solution, escapes partially unused, and on the other, the intact outer layer prevents the bath from coming in contact with the interior of the anode. The cast anodes suspended to the ends of the conducting 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 centre, and the first on the ends of the rods. These disadvantages, 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 spongy remnants are thoroughly washed in hot water, dried and sold. The 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. The surface of the anodes suspended in the baths should be at least as large as that of the articles to be nickeled ; it is, how- ever, preferable that they should present twice or three times the surface, in order that the bath may be kept thoroughly saturated with nickel. 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 1 84 ELECTRO-DEPOSITION OF METALS. are subject to concussion, in consequence of which they crumble much more quickly than when remaining quietly in the bath. In the morning, before nickeling is commenced, the anodes will frequently show a reddish tinge, which is generally ascribed to a content of copper in the bath or in the anodes. This red- dish coloration also appears when an analysis shows the anodes as well as the bath to be absolutely free from copper. It is very likely due to a small content of cobalt, from which nickel anodes can never be entirely freed. It would seem that by the action of a feeble current cobaltous hydrate is formed, which however immediately disappears on conducting a strong current through the bath. The anodes are supported by nickel wire o. II to 0.19 inch thick, or by strips of nickel sheet riveted on. If after working for some time a nickel bath has become alkaline, which can be readily determined by testing with litmus- paper, its neutrality or a slightly acid reaction can be restored in a few minutes by the addition of either citric, sulphuric, acetic, or boric acid, according to the composition of the bath. On the other hand, when the bath contains too much free acid, it is removed by the addition of spirits of sal ammoniac, am- monium carbonate, potash, or by boiling with nickel carbonate, the choice of the remedy depending on the composition of the bath. The process of electro-nickeling. Next to the correct compo- sition of the bath and the proper selection of the anodes, the success of the nickeling process depends on the thorough cleans- ing of the objects and the correct current- strength. The directions for the removal of grease, etc., given on p. 156, also apply to objects to be nickeled. In executing the manipulations, it should always be borne in mind that though dirty, greasy parts become coated with nickel, the deposit im- mediately peels off by polishing, because an intimate union of the deposit with the basis-metal is effected with only perfectly clean surfaces. Touching the cleansed articles with the dry DEPOSITION OF NICKEL AND COBALT. 185 hand must be strictly avoided ; but, if large and heavy objects have to be handled, the hands should first be freed from grease by brushing with lime and rinsing in water, and be kept wet. As previously mentioned, the cleansed objects must not be exposed to the air, but immediately placed in the bath, or, if this is not practicable, be kept under clean water. While copper and its alloys (brass, bronze, tombac, German silver, etc.), as well as iron and steel, are directly nickeled, zinc, tin, Britannia and lead are generally first coppered or brassed. With a suitable composition of the nickel bath and some ex- perience, the last-mentioned metals may also be directly nick- eled ; but, as a rule, previous coppering or brassing is preferable, the certainty and beauty of the results being thereby consider- ably increased. By many operators it is preferred to copper, iron and steel articles before nickeling, it being claimed that by so doing better protection against rust is secured. However, compara- tive 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 long as if it had previously been slightly cop- pered. 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 re- moval of grease, but with objects carefully cleansed according to the directions given on p. 156, previous coppering is not necessary. The case, however, is different if the copper deposit is pro- duced in order to act as a cementing agent for two nickel de- posits. If, for instance, parts which have previously been nickeled and from which the old deposit cannot be removed by mechanical means, are to be re-nickeled, coppering is re- quired, because the new deposit of nickel adheres very badly to the old. Where articles are to be protected as much as 1 86 ELECTRO-DEPOSITION OF METALS. possible from rust, coppering is advisable, but the best success is attained by a method different from the one generally pur- sued. For nickeling, for instance, parts of bicycles which are exposed to all atmospheric influences, the parts are first pro- vided with a thick deposit of nickel, then with a thick coat of copper, and finally, again nickeled, they thus being twice nickeled. It has previously been mentioned that every de- posit is formed net-like, the meshes of the net being larger or smaller, according to the nature of the metal deposited. If now thick layers of two different metals are deposited one on the top of the other, the net-lines of one deposit do not con- verge into those of the previous deposit, but are deposited between them, thus consolidating the net. It will now be readily understood that by the subsequent polishing the further consolidation of the deposits will be far more complete than when the basis-metal receives but one deposit, which is to be consolidated 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 re- spective baths of one and the same metal exert an influence upon the greater or slighter density of the net. The objects should never be suspended in the bath without cur- rent ', the baths, with few exceptions, exerting a chemical action upon many metals which is injurious to the electro-plating pro- cess, and especially with the nickel bath is it necessary to con- nect the anode-rods and object-rods before suspending the articles in the bath. The suitable current- strength has already been fully discussed on p. 89 et seq. (" Electro-plating Arrangements in Particu- lar"), and referring the reader to that section we may here be comparatively brief. In that section it has been said that the surfaces of objects to be nickeled must be in due proportion to the effective zinc surface of the battery if the latter be used for generating the DEPOSITION OF NICKEL AND COBALT. 1 87 current ; further, the surface of anodes suspended in the bath must be at least equal to that of the objects, though in most cases it is better that it should be larger On p. 89 et seq., it has also been explained how, according to circumstances, the elements have to be coupled to a battery in order to be sure of success. Two Bunsen elements, coupled one after the other, yield for nearly all nickel baths the electro -motive force re- quired for the reduction of the nickel ; for baths with great re- sistance it will, however, be better, especially when the filling of the elements is no longer fresh, to couple three elements one after the other, and to neutralize a momentary excess of cur- rent by the resistance board. An error is frequently committed in nickeling 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, which is due to the reduction of the nickel with a coarse grain in consequence of too powerful a current, 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 thereby prevented from acquiring greater thickness. Especially do those objects suspended on the ends of the rods nickel with great ease ; this evil can be avoided by hang- ing on both ends of the rods a strip of copper-sheet about 0.39 inch wide, and of a length corresponding to the depth of the bath. The following criteria may serve for judging whether the nickeling progresses with a correct current-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 regularity are an indication of the operation progressing regularly. If, after two or three minutes, the ob- 1 88 ELECTRO-DEPOSITION OF METALS. jects 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 resistance board, or, if the entire volume of current gen- erated already passes into the bath, the object-surface has to be diminished, 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 resistance board, or uncoupling a few elements, or diminishing the anode-surface, or finally by sus- pending more objects in the bath. These criteria also apply to nickeling with the dynamo. The density of current most suitable for nickeling copper, copper-alloys, iron and steel is O.6 ampere per 15.5 square inches, while zinc previously coppered requires 1.2 amperes. It will be seen that in nickeling zinc objects greater density of current and higher tension are required. If the current is not of sufficient strength, black streaks and stains are formed, zinc is dissolved and the nickel bath spoiled. These evils are frequently complained of by nickel-platers who have not a clear perception of the prevailing conditions (see polarizing current). A vigorous evolution of gas must take place on the zinc ob- jects, otherwise a serviceable deposit will not be obtained. In most cases the electro-plater will in a few days learn correctly to judge the proper current-strength by the pheno- mena presented by the objects, and if he closely follows the directions given but few failures will result. It may here be again repeated that the use of a voltmeter as well as of a resistance board 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-plat- ing plant. The density of current most suitable for nickeling copper, DEPOSITION OF NICKEL AND COBALT. 189 copper-alloys, iron, and steel varies between 0.4 and 0.8 ampere per 15.5 square inches, while zinc, after previous coppering, re- quires 1.3 to 1.5 amperes. It is in all respects advisable first to cover the objects by means of a strong current, i. e. t to give the first deposit rapidly, in order to withdraw the metals from the action of the bath, and then finish the operation after reducing the current to a suitable strength. With a current thus regulated the objects may be allowed to remain in the bath for hours and even for days. It is further possible to nickel by weight and attain de- posits of considerable thickness. If very thick deposits of nickel are desired, the objects must be frequently turned in the bath, as the lower portions nickel stronger than the upper; further, as soon as the deposit ac- quires a dull bluish lustre it has to be thoroughly scratch- brushed, in doing which, however, the objects must not be allowed to become dry. After scratch-brushing it is advisable to cleanse the deposit once more with the lime-brush, and after rinsing replace the objects in the bath. If burnt places cannot be brightened and smoothed with the scratch-brush, the de- sired end is readily attained with the assistance of emery paper or pumice. For solid nickeling it suffices in most cases to allow the ob- jects to remain in the bath until the dull bluish lustre appears, this being an indication that the deposit has acquired consider- able thickness, and will not take a further regular deposit. If such objects are permitted to remain longer in the bath without scratch-brushing, the dull bluish tone soon passes into a dull gray, and all the metal deposited in this form must be polished away in order to obtain a bright lustre. Whether the deposit of nickel is sufficiently heavy for all ordinary demands is, according to Fontaine, shown by rubbing a nickeled corner or edge of the object rapidly and with ener- getic pressure upon a piece of planed soft wood until it be- comes hot. The nickeling should bear this friction. This test can be recommended as perfectly reliable. ELECTRO-DEPOSITION OF METALS. 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.). For flat objects it is sufficient to suspend them between two rows of anodes ; round objects with a large diameter should be quite surrounded with anodes, and be as nearly as possible equi- distant from them. This arrangement should especially not be neglected where a heavy and uniform deposit of nickel is to be given to round or half-round surfaces for instance, large half- round stereotype plates for revolving presses. While for smooth articles the most suitable distance of the anodes from the objects is 3 ^ to 5 ^ inches, for objects with depressions and hollows 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 deposit than the hollows ; 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 hollows, is to be preferred. This, of course, renders it necessary for a workman to stand alongside the bath and execute the operation by hand ; but as the small anode can be brought within a few millimetres of the surface of the article, and at this distance slowly moved around it, a correspondingly thick deposit is in a short time formed. At any rate baths in which objects with depressions and hollows are to be nickeled must possess greater resistance than baths for nickeling flat articles, and it is inexplicable why a bath with a large content of ammonium chloride and conse- quently slight conducting resistance can be recommended, as has been done, for nickeling hollow articles. In nickeling lamp-feet of cast-zinc, the use of the hand-anode can scarcely be avoided if the depressed portions also are to be provided with a uniformly good deposit. Moreover, zinc arti- DEPOSITION OF NICKEL AND COBALT. 191 cles form an exception to the general rule in so far as by reason of the highly positive properties of zinc the resistance of the bath may be slighter than for baths for nickeling copper and its alloys, as well as iron and steel. Besides the above-mentioned general rules for nickeling,, which also hold good for other electro-plating processes, 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, several times to move them up and down ; 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 cov- ered surface acquires only a slight deposit. That the objects must not touch the anodes need scarcely be mentioned. Objects with depressions and hollows should be suspended in the bath so that the air in the hollows can escape, which is effected by turning the depressions upwards, or, if there are several depressions on opposite sides, by turning the articles about after being introduced into the bath. Air-bubbles re- maining in the hollows prevent contact with the solution, no deposit being formed on such places. It remains to say a few words in regard to the so-called polar- izing phenomena. In the theoretical part, it has been shown that by dipping two plates of different metals in a fluid a counter ELECTRO-DEPOSITION OF METALS. or polarizing current 'is generated, which is the stronger the further the two metals are removed from one another in the series of electro-motive force, and the more they differ in their electrical behavior. If the anodes in a nickel bath are of nickel and the articles of copper, the counter-current will be slight, because copper and nickel stand together in the series of electro-motive force (p. 15). The counter-current, however, becomes greater when iron objects are hung in the bath, and greatest with zinc surfaces which are to be nickeled, because zinc, being the most electro-positive metal, differs widely in its behavior from nickel. Now, since the counter-current flows in a direction opposite to that of the current introduced in the bath, the latter is weakened, and the more so the stronger the counter-current is. This ex- plains 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 annul the effect of the principal current, and even to reverse the latter, the consequence being that, in the first case, the formation of the deposit is interrupted, and, in the latter, that the deposit is again destroyed, and the metals of which the articles consist dissolve and contaminate and spoil the bath. To avoid this, a main current must be conducted into the bath, which, by its sufficiently large electro-motive force, can overcome the counter-current, and the consequences of the reversion of the current can be prevented by using the galvano- meter and observing the deflection of its needle, which (accord- ing to p. 95) in proper time indicates the appearance of a re- versed 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 annul 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 elements, with two acids or f ' DEPOSITION OF NICKEL AND COBALT. 193 dynamo-electric machines with at least 4 volts' tension, are generally used ; it is, however, well to acquaint the operator with all possible contingencies, and to explain the reason why the articles are preferably covered with a strong current. Sprague recommends an initial current of 5 volts' tension, but in most cases one of 3.5 volts suffices for nickeling iron and copper alloys. Nickeling en masse of small and cheap objects. This is effected by stringing the objects, if feasible, upon a copper wire, and placing a large glass bead between every two objects, to prevent the surfaces from sticking together in the bath. Such objects being generally only slightly nickeled, it suffices to allow them to remain for a few minutes only in the bath with a strong current, it being advisable to diligently shake the bundles in order to effect a change of position of the objects and prevent their touching one another, notwithstanding the glass bead placed between them. Very small objects, such as rivets, pins, etc., which cannot be strung upon wire, are nickeled in a stoneware dipping basket. 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 constantly 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 sieve (Fig. 107) and constantly shakes 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 one of brass wire 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 an unnecessary deposit of nickel upon the basket the latter is coated with asphalt varnish and at a distance of about 13 194 ELECTRO-DEPOSITION OF METALS. 2^ to three 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 quickly obtained, especially if with the other hand the articles are incessantly stirred by means of a glass or wooden rod. O 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 FIG. 107. 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 en masse. It will be further discussed under " Cobalting." Stripping nickeled articles. Defective nickeling must, as a rule, be completely removed before the objects can be re- nickeled, since the second deposit adheres badly to the previous ore, especially if the latter has become dry. The removal of a DEPOSITION OF NICKEL AND COBALT. 195 nickel-deposit is in most cases a disagreeable labor, which, how- ever, can most assuredly be saved if the utmost care and pains- taking cleanliness are observed in freeing the articles from grease and in regulating the current. For the removal of the nickel coating the following stripping acid, which may be used either cold or tepid, has been recommended : Sulphuric acid of 66 Be, 4 Ibs. ; nitric acid of 40 Be., i Ib. ; water about I pint. First put the water in a stoneware jar and cautiously add, a little at a time, the sulphuric acid, since considerable heat is generated when this acid is mixed with water. When the entire quantity of sulphuric acid has been added, pour in the nitric acid, when the bath is ready for use. In making up the stripping bath, the proportion of the acids may be varied, but the foregoing will be found to answer every purpose. An addition of 8 ozs. of potassium nitrate to the bath has also been recommended. When stripping nickel-plated articles in the above bath it is necessary to watch the operation attentively, since some articles are very lightly coated and a momentary dip is frequently suf- ficient to deprive them of their nickel. Other articles which having been thoroughly well nickeled, require from some acci- dental cause to be stripped and re-nickeled, will need immer- sion for several minutes indeed well-nickeled articles may oc- cupy nearly half an hour in stripping before the underlying sur- face is entirely freed from nickel. 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 ascertain how the stripping progresses ; and the moment it is found that the nickel has quite disappeared from every part, the article must be plunged into clean cold water. It is absolutely necessary that the work should not remain in the stripping solution one instant after the nickel is removed. When the stripping has been properly effected the underlying metal exhibits a bright, smooth surface, giving little evidence of the mixture having acted upon it. 196 ELECTRO-DEPOSITION OF METALS. Many platers, however, prefer to remove the nickel-coating mechanically by brushing with emery. From depressions as much as possible is 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 deposits peeling off in polishing. It has also been proposed to remove the nickel from the articles by means of the battery or dynamo-machine by making them the anodes in a nickel bath ; but in this case a separate solution should be employed for the purpose. As a remedy against the yellowish tone of the nickeling, Pfan- hauser recommends suspending the nickeled articles, immedi- ately 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. The following is a brief resume of the principal pheno- mena 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. Reasons: The current fs either too feeble to effect the reduction of nickel, and the colora- iton is in consequence of the chemical action of the nickel solu- tion upon the metals constituting the objects. Remedy: In- crease the current or diminish the area of suspended objects ; also examine whether the current actually passes into the bath, otherwise clean the places of contact. 2. A deposition of nickel takes place, but it is dark or spotted or marbled, even with a sufficiently strong current. Reasons: The bath is either alkaline, which has to be ascertained by lit- mus 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 ^ DEPOSITION OF NICKEL AND COBALT. 197 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 ad- mixture of copper, the production of dark tones being fre- quently 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 pickl- ing of the articles have not been thoroughly done, which is remedied by again cleaning 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. 3. A yellowish tinge of the nickeling. Reasons: See under 2 ; or, with cast-iron an insufficient metatlic 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 dull gray-black, especially on the lower edges and corners. Reason: Too strong a current. Rem- edies: Regulating the current, or hanging in more objects, or uncoupling elements. Frequent turning of the articles. 5. The nickeling is white, but readily peels off by scratching with the finger-nail or by the action of the polishing wheel. Reasons: The current is too strong, which is remedied as under 4 ; or, the bath is too acid this is remedied by the addition of spirit of sal ammoniac, potassium carbonate, or nickel car- bonate, according to the composition of the bath : or, insuffici- ent cleaning and pickling, which is remedied by thorough clean- ing after removing the defective deposit, or, if it cannot be en- tirely 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 air bubbles are in- closed in cavities ; or, faulty arrangement of the anodes. Remedy: Removal of the causes. 198 ELECTRO-DEPOSITION OF METALS. 7. The deposit appears with small holes. Reason: A deposit 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 ; or the portions covered by the suspending wire show dark lines. Reason: Insufficient con- ducting power of the bath. With large depressions this cannot be remedied by the addition of a suitable conducting salt, but requires 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 of longer time require certain additions in order to keep their action constant. By " refreshing" is not understood the small addition of acid or alkali from time to time required for restoring the original reaction of the baths, but additions intended to increase the metallic content and diminished con- ductivity. The metallic content is increased by boiling the bath with some of the nickel salt used in its preparation, while the con- ductivity is improved by adding, at the same time, so much conducting salt as is necessary to restore the electro-motive force originally required. Nothing definite can, of course, be said in regard to the quantity of such additions, it being advis- able to observe their effect on a small portion of the bath, so as to be sure not to spoil the entire bath. Nickel baths bear, as a rule, refreshing several times, but as in the course of time they take up impurities, even when the greatest care is exercised, it is best to refresh them at the utmost twice, and then to renew them entirely. The treatment of the articles after nickeling as well as after all electro-plating processes has already been described and DEPOSITION OF NICKEL AND COBALT. 1 99 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 saw-dust is absolutely necessary, and subsequent dry- ing in a drying chamber is also a great safeguard as regards stability and protection against rust. Nickel deposits are polished upon felt disks or bobs of cloth, muslin, or flannel, with the use of Vienna lime, rouge, etc. (See "Polishing," page 137.) 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. Knife-blades and surgical instruments with sharp edges require special care in polishing, which will be re- ferred to later on. After polishing, the nickeled objects, especially those with depressions, have to be freed from polishing dirt by brushing with hot soap-water or dilute hot caustic lye, then rinsed in hot water and dried in clean, fine saw-dust. Objects which are not required to be polished, but left dead, that is, just as they come out of the nickel bath, should be taken from the bath one at a time, and at once plunged into perfectly clean hot water for a few moments, and then placed aside to dry spontaneously. Dead nickel being very readily stained or soiled, even when touched with clean hands, the work should be handled as little as possible. 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 intel- ligence of the operator than any other electro-plating process, it requiring only an accurate consideration of the relations of the electric behavior of zinc towards nickel ; consequently, a knowledge of the strength of the counter-current and of the chemical behavior of zinc towards the nickel solution, which 200 ELECTRO-DEPOSITION OF METALS. may readily dissolve the zinc ; further, a correct estimation of the current-intensity required for a determined zinc surface, as well as of the proper anode-surface, and the most suitable com- position and treatment of the nickel baths. With due observation of these relations, the nickeling of sheet zinc is accomplished as readily as that of other metals ; and the proposals to first cover the sheets in a bath with a strong cur- rent, and finish nickeling with a weaker current, or to amalga- mate the zinc before nickeling, need not be considered. Below the condititions 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 disks (buffs) formed of separate pieces of cloth. The polishing lathes run with their points in movable bearings se- cured in a hanging cast-iron frame by a set screw and safety keys, or preferably as shown in Fig. 94, p. 140, since with this construction an injury to the grinder by the lathe jumping out is impossible. The buffs, when new, have on an average a diameter of 12 to 1 6 inches, and a width of 5^ to 8 inches; the principal point in the construction of these bobs is uniform weight on all sides, the quiet running and the possibility of a good polish without great exertion depending on this. Bobs not well balanced run unsteadily and jump, thereby producing fine scratches upon the sheet. The bobs are constructed as follows : A square piece of cloth is folded fourfold and the closed point cut off with a pair of scissors, so that on unfolding the cloth the hole produced by the cut is exactly in the centre of the cloth disk; according to the diameter of the spindle more or less is cut away, but in every case just sufficient that the piece of cloth can be conven- iently pushed upon the spindle. The latter, which is provided with a pulley and a hoop against which the pieces of cloth fix themselves, as well as with a nut and screw for securing them, is vertically fasiened in a vise, and the separate pieces of cloth are DEPOSITION OF NICKEL AND COBALT. 201 FIG. 1 08. pushed upon it so that the second piece placed in position forms an angle of about 30 (Fig. 108) 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 disk, 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 pullley the bob is revolved, a sharp knife being held against it to remove the projecting corners. In polishing sheet zinc the bobs make 2400 to 3000 revolutions per minute, according to whether finely rolled or rougher sheets are to be polished. For the purpose of polishing or grinding, the operator places the sheet upon a support of hard wood of the same size and form as the sheet, and grasps the two corners of the sheet nearest to his body, together with the support, with the hands, applying with the balls of the hands, the necessary pressure to hold the sheet upon the support. The lower half of the sheet, that furthest from the body, rests upon the knees of the opera- tor, and with them he presses the sheet against the polishing disk, 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 2 inches wide is applied by means of a brush to the centre of the sheet in the visual line of the operator, and the revolving bob is impregnated with Vienna lime by holding a large piece of it against it, when polishing of the lower portion of the sheet begins. When about | of the surface has thus been polished, the sheet is turned round and the remaining portion subjected to the same process. The sheet is then closely inspected to see whether there are still dirty or dull places, and, if such be the case, it is polished once more after moistening it with some oil and again impregnating the bob with Vienna lime. The sheet being sufficiently polished, the 202 ELECTRO-DEPOSITION OF METALS. oil and polishing dirt are removed by dry polishing, after pro- viding the bob with sufficient Vienna lime, so that the sheets when finished show no streaks of dirt or oil. Self -acting sheet polishing machines have been constructed by Dr. Sackur, F. Rauber, Eliachoff, and others. Such machines give a very good polish, but have the disadvantage that thin sheets when polished upon them become wrinkled or wind up on the polishing roller. In order to explain the principle upon which these machines are constructed, a description of F. Rauber's sheet grinding and polishing machine is given. With this machine metallic sheets of any length can be polished ; by the simultaneous lateral and longitudinal motion of the sheets a faultless polish is obtained, streaks- and scratches being especially avoided. FIG. 109. The machine essentially consists of the gearing A and the actual polishing machine B, Figs. 109, no, in. The gearing A consists of the two standards a a, the shaft b, a fast and loose pulley, c c, the large driving-wheel d, a small driving-wheel, e, and the eccentric/. The polishing machine B consists of the wooden frame g with wooden plate h, the two standards i i, the polishing roller , the iron counter-roller /, the expanding contrivance m, which is DEPOSITION OF NICKEL AND COBALT. 203 *> IB ~y.-.^hr.-.-.:.^fl m 1 - effected by means of three spiral springs, the gearing n with the rope-drum o, the rope with the tongs g, and the shaking arrange- ment x. 204 ELECTRO-DEPOSITION OF METALS. The machine is set in motion by the engaging coupling x on the gearing A. The shaft of the gearing makes about 200 revo- lutions per minute, and the polishing roller k is revolved by a belt from the driving-wheel d. At the same time the gearing n is set in motion by a belt from the driving-wheel e, in conse- quence of which the rope is wound upon the drum o, and the tongs on the rope draw the sheet to be polished under the polishing roller. If the sheet is to go back, the rope-drum o is disengaged by means of the coupling y t and the polishing roller k, which moves lightly upon the counter-roller /, draws the sheet back. To prevent the sheet from jumping back, the brake r is provided on the rope-drum o. By the treadle r^ the workman is enabled to transport the sheet slowly or rapidly, as may be required. To move the sheet forward, the rope-drum o is again engaged. The lateral motion of the sheet is effected by the shaking contrivance x. From the eccentric/, of the gearing A, the slide rod t is con- nected with the joint lever x and the latter by the pin s with the table plate h, whereby the latter when the machine is running is moved to the sides. The centre of motion of the table plate is upon the pin v. To regulate the pressure of the sheet against the polishing roller, the expanding arrangement m is placed under the table plate h. It consists of three vertical bolts with spiral, springs, each of which can be screwed up and down by a nut. To facilitate the lateral motion of the table plate h, the bolts of the expanding contrivance m are provided with rolls which press against the plate. If the tension is sufficient and a sheet is to be introduced, it is only necessary to draw the table plate down by means of the treadle w, to push the sheet under the polishing roll k, and to engage the tongs g. In front of the gearing A is a table for the reception of the sheet, as shown in the illustration. The sheets are best freed from grease 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 DEPOSITION OF NICKEL AND COBALT. 2O5 and passed through a hair sieve, rub over the sheet in the di- rection at a right angle to the polishing streaks, applying a very gentle pressure. For the wet process dip a wet piece of cloth or a soft sponge free from sand into a paste of impalpable Vienna lime, whiting, and water, and go carefully over the sheet so that no place remains untouched. Then rinse the sheet under a powerful jet of water, best under a rose, being especially care- ful to remove all the lirne, going over the sheet, if necessary, with a soft wet rag and observing whether all portions appear evenly moistened. If such be the case, the cleaning is com- plete, otherwise the sheet has to be treated once more 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. Some manufacturers nickel the cleansed sheets without previ- ous 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 sal ammoniac, according to the area 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 nickel- ing 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 phenomena which must be mentioned. The nickel deposit upon brassed sheets shows a decidedly whiter tone than that upon coppered sheets, and brassing would deserve the preference if this process did not require extraordinarily great care in the proper treatment of the 206 ELECTRO-DEPOSITION OF METALS. 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 separates uniformly, adheres firmly, and is not porous, the correct progress of the operation being recognized by the color being more like tombac, and not pale yellow or greenish. Where 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 the 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, III. or V., given under " Cop- pering " serves, to which, for this special purpose, more potas- sium 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 DEPOSITION OF NICKEL AND COBALT. 2O/ become dull or even discolored ; and they should come from the bath with a full or at least half lustre. When taken from the copper bath the sheets are thoroughly rinsed in a large water reservoir, the contents of which must be frequently re- newed, 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 immedi- ately brought into the nickel bath, it being best to suspend two, three, or four plates 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 plates 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. Every separate nickel bath in which sheets are to be nickeled must be fed with the full current of a dynamo-machine, one of 250 to 300 amperes with 4 volts' tension being generally used. According to the number of sheets, generally 6 to 8, each 20x20 inches, to be nickeled, the dimensions of the vats are as follows : 63 inches long, 15^ inches wide, and 255^ inches deep, or, 83 inches long, 15^ inches wide, and 25^ inches deep. One to two minutes suffice to give 6 sheets a sufficiently thick deposit of nickel with a dynamo-machine of the above-mentioned capacity, and 2 to 3 minutes for eight sheets ; and it may be accepted as a rule that, with a bath of good conductivity, a density of cur- rent of from 1.4 to 1.5 amperes and 5 volts' tension is required per 15.5 square inches of zinc surface for the solid nickeling of the sheets. For nickeling zinc in baths conducting with diffi- culty, for instance, a simple solution of sulphate of nickel and ammonia without the addition of conducting salts, or in baths containing boric acid, 1.3 to 1.4 amperes and 6 to 7 volts, must be allowed per 1.55 square inches of zinc surface if the nickeling is to be effected in the above-named space of time. A density of current of 1.4 to 1.5 amperes and 4 to 4^ volts, at which the sheets have to remain in the bath for 3 minutes, is the most suitable, the deposit thus obtained being in every respect fault- less, provided the nickel bath is of proper composition. 208 ELECTRO-DEPOSITION OF METALS. For nickeling sheet zinc rolled anodes are, as a rule, only used, except when working with baths containing boric acid. The anode surface must at least be equal to that of the zinc surface ; the distance between the anodes and the sheets should be from 3 to 3 ^ inches, and when the current-strength is some- what scant the distance may be reduced to 2^ inches. The nickel anodes have to be taken from the bath once daily and scoured bright with scratch-brushes and sand ; for the rest, all the rules given for nickel anodes are valid. Baths used for nickeling sheet zinc soon become alkaline in consequence of the powerful current used, which is shown by red litmus-paper turning blue ; the alkalinity also manifests itself by the bath becoming turbid and the nickeling not turn- ing out a pure white. The slightly acid reaction is restored by citric acid solution. The appearance of the dreaded black streaks and stains is due either to the current itself being too weak or to its having been weakened by an extremely great re- sistance of the nickel bath ; also to an insufficient metallic sur- face of the anodes, which may be either too small or not suffi- ciently 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 augmented by the addition of nickel salt, and the bath filtered at certain intervals. When the conductivity abates, it has to be restored by the addition of conducting-salt. When the sheets have been sufficiently nickeled, they are allowed to drain off, then plunged into hot water, and, after re- moving the binding-screws, dried by gentle rubbing with fine sawdust free from sand and passed through a fine sieve to separate pieces of wood. In all manipulations, the unnickeled 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, however, only DEPOSITION OF NICKEL AND COBALT. 2Og moderately moistened with oil, and not too much Vienna lime applied to the bob. Polishing is done first in one direction and then in another, at a right angle to this first. After polishing, the sheets are finally cleansed with a piece of soft cloth and impalpable Vienna lime, after which they should show a pure white lustrous nickeling, free from cracks and stains, and bear bending and rebending several times without the nickeled de- posit breaking or peeling off. Nickeling of tin-plate. For elegant and durable nickeling tin-plate also requires previous coppering. The deposit is effected with a less powerful current than for sheet zinc. Scouring is done as described for sheet zinc, also polishing of the nickeled tin-plate. Nickeling copper and brass sheets. The treatment of these sheets differs from that of sheet zinc in that the rough sheets are first brushed with emery and then polished with the bob. After treating the sheets with hot caustic lye or lime-paste, they are pickled by brushing them over with a solution of I 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 must not be too strong. Nickeling of sheet-iron and sheet-steel. Only the best qualtiy of sheet should be used for this purpose. After rolling, the sheets are freed from scales by pickling, then passed through the fine rolls, and finally again pickled. If the nickeled sheets are not to exhibit a high degree of polish, it suffices to brush them before nickeling with a large broad fibre brush (p. 136) and emery No. oo. But for a high lustre, such as is generally demanded, the sheets have first to be ground. For fine grind- ing the pickled sheets broad massive cylinders of poplar wood are used, which are covered with leather and turned like the disks described on p. 132. These cylinders 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 cylinders are coated with glue and rolled in emery No. 100 to 120, according 210 ELECTRO-DEPOSITION OF METALS. to the condition of the sheets, while emery No. oo is applied to the cylinders used for the fine grinding. The grinding is suc- ceeded by brushing, as described on p. 132. After preparing a sufficiently smooth surface, the sheets are at once rubbed with a rag moistened with petrolenm, or, if pre- ferred, with a rag and pulverized Vienna lime ; they are then scoured wet in the manner described for sheet-zinc, p. 204. The scouring material must be liberally applied, especially if the sheets are to be directly nickeled without previous coppering, as is advisable. After rinsing off the lime-paste, the sheets are brushed over with very dilute sulphuric acid (I part acid to 25 water), rinsed off, then lightly brushed over once more with lime- paste, again carefully rinsed, and immediately brought into the nickel bath. The current should be neither too strong nor too weak, but regulated so that the nickeling is of sufficient thickness in 15 to 20 minutes without showing a tendency to peel off. It is not advisable to try to obtain a heavy deposit in a shorter time, be- cause it would lack density, which is the principal requirement 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 and 212 F., to expel any moisture from the pores, and then to polish them with Vienna lime and oil or with rouge. Nickeling of wire. Nickeling of wire of iron, brass, or copper is scarcely ever done on a large scale ; it is, however, believed that the nickeling of iron and steel wires for instance, piano- stringsmight be of advantage to prevent rust or at least to re- tard the commencement of oxidation as long as possible. To nickel single wires cut into determined lengths, according to the general rules already given, is simple enough ; but this method cannot be pursued with wire several hundred yards long, rolled in coils, as it occurs in commerce. Nickeling the wire in coils, however, cannot be done, as only the upper windings ex- DEPOSITION OF NICKEL AND COBALT. 211 posed to the anodes would acquire a coat of nickel. Hence it becomes necessary to unwind the coil, and for continuous work- . y M ' ti i ing pass the wire at a slow rate through the cleansing and pick- ling baths, as well as the nickel bath and hot water reservoir, as 212 ELECTRO-DEPOSITION OF METALS. shown in Fig. 112 in cross-section, and in Fig. 113 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. 1 13 four wires run over the four rolls a, mounted upon a common shaft, to the rolls b upon the bottom of the vat A, whereby they come in contact with a thickly fluid lime-paste in the vat, and are freed from grease. From the rolls b the wires run through the wooden cheeks i, lined with felt, which retain the excess of lime-paste, and allow it to fall back into the vat. The wires then pass over the roll c to the roll d. Between these two rolls is the rose g, which throws a strong jet of water upon the wires, thereby free- ing them from adhering lime-paste. The roll d y as well as its axis, is of brass, and to the latter is connected the negative pole of the battery or dynamo, so that by carrying the wires over the roll d negative electricity is conducted to them. From the roll d the wires run over the roll-bench s (Fig. 113) to the vat C, which contains the nickel solution, so that they are subjected to the action of the anodes arranged in this vat 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 apparatuses are not shown in the illustra- tion), to be again wound in coils. In case a high polish is re- quired, the nickeled wires may be run under pressure through leather cheeks dusted with Vienna lime. Nickeling wire-gauze. Messrs. Louis Lang & Son obtained, in 1 88 1, a patent for a method of nickeling wire gauze, or wire to be woven into gauze, more especially for the purpose of paper manufacture. These wires, which are generally of copper or brass, are liable to be attacked by the small quantities of chlorine which generally remain in the paper pulp, by which the gauze wire eventually suffers injury. To nickel wire before it is woven, it is wound on a bobbin and immersed in a nickel bath in which it is coated with nickel in the usual way ; it is then unwound and rewound on to another bobbin, and reimmersed DEPOSITION OF NICKEL AND COBALT. 213 in a nickel bath, as before, so as to coat such surfaces as were in contact with each other and with the first bobbin. To deposit nickel on the woven tissues it may either be coated in its entire length, as it leaves the loom, or in detached pieces. For this purpose the wire gauze is first immersed in a pickle bath, and next in the nickel solution. On leaving the latter it is rinsed and then placed in a hot air chamber, and when thoroughly dry may be rolled up again ready for use. Nickeling of knife-blades, sharp surgical instruments, etc. Considerable 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 instruments 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 necessary to free them at once from grease and bring them into the bath. But instruments which have been used or by bad treatment have become partly or entirely covered with rust must be first freed from rust by chemical or mechanical treat- ment and then polished. The marks left by the stone or emery wheel are effaced by means of the circular brush, this treatment being necessary to obtain perfect nickeling. But in brushing the edges are rendered dull if special precautionary measures are not used. For instance, the edge of a knife-blade must never come in contact with the brush. This is prevented by firmly pressing the blade flat upon a soft support of felt or cloth, so that the edge sinks somewhat into the support, with- out, however, cutting into it. The edge is then held downward, and thus together with the support brought against the revolv- ing brush. In this manner the blades may be vigorously brushed without fear of spoiling the edges. The treatment in 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 214 ELECTRO-DEPOSITION OF METALS. support, the same as in polishing, After thorough rinsing in clean water the separate pieces, without being previously cop- pered, are brought directly into the nickel bath, the composi- tion of which must, of course, be suitable for nickeling steel articles. The instruments are first coated with the use of a strong current, so that the deposition takes place slowly and with great uniformity. In suspending the articles in the bath, care should be had that neither a point nor an edge is turned towards the anodes. It is best to use a bath with anodes on one side only, and to suspend the blades with their backs towards the anodes. If, for any reason, the instruments are to be suspended between two rows of anodes, the edges should be uppermost, as near as possible, to the level of the bath ; but they should never hang deep or downwards. After nickeling the instruments are polished for high lustre, but must always be exposed upon a soft support, as above de- scribed, to the action of a felt disk, or, still better, of a cloth bob. Nickeling of electrotypes, cliches, etc. The advantages of nickeling electrotypes, etc., over steeling will be discussed under " Steeling," and hence only the most suitable composition of the nickel baths and the manipulations required will here be given. The nickel baths according to formula III. (page 174) and formula VII. (page 177) are the most suitable for simple nickel- ing, 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 great hardness. With nickeled electro-plates three times as large an edition can be printed as with plates of the same material not nickeled. 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 behavior, the greatest degree of hardness being attained with an addition of cobalt DEPOSITION OF NICKEL AND COBALT. varying between 25 and 30 per cent. For this deposit the term hard nickeling is proposed, the most suitable baths for the pur- pose being prepared according to the following formulae : 1. Nickel-ammonium sulphate 21.16 ounces, cobalt-ammonium sulphate 5.29 ounces, ammonium sulphate 8.8 ounces, water 15 quarts; or, II. Nickel-ammonium sulphate 21. 16 ounces, cobalt-ammonium sulphate 5.29 ounces, crystallized boric acid 10.58 ounces, water 15 quarts. Bath No. I. is prepared by simply dissolving the salts in heated water, and, in case the bath is too acid, adding spirits of sal ammoniac until blue litmus-paper is only slightly red- dened. It is best to use rolled and cast anodes in equal pro- portions ; and when the bath becomes alkaline to restore its original slightly acid reaction by the addition of citric acid. To prepare bath No. II. dissolve the constituents by boiling; and in case not entirely neutral metallic salts have been used, add to the hot solution, with constant stirring, I to I ^ ounces of nickel carbonate for the neutralization of free sulphuric acid which may be present. This bath must not be neutralized, but worked with its strongly acid reaction, mixed anodes being also used. 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. 174 and 177), and the process of h:rd 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-cop- per o.i i inch thick, and ^ to I inch wide, of the form shown in Fig. 114. The printing surface is freed from grease by brushing with lime-paste, rinsed in water, and then brushed with a clean brush to remove the lime from the depressions. The plates are then hung in the bath and covered with a strong current. When everywhere coated with nickel the current is weakened and the deposit allowed gradually to augment. 216 ELECTRO-DEPOSITION OF METALS. With an average duration of nickeling of 15 to 20 minutes, with 2.8 to 3 volts, the deposit will, as a rule, be sufficiently resisting. 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 FIG. 114. 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 vermilion. Recovery of nickel from old baths. At the present low price of nickel its recovery from old solutions scarcely pays. The uselessness 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 with the further manipulation is out of proportion to the value of the DEPOSITION OF NICKEL AND COBALT. 2I/ nickel recovered ; and, in the second case, the reduction of the foreign metals is inconvenient and connected with expenses making it unprofitable. Urquhart proposes the following plan for recovering nickel from old solutions ; Make a saturated solution of ammonium sulphate in warm water, and add to it the old nickel-plating solution with constant stirring, and, after the lapse of a few minutes, a granular precipitate of the double sulphate of nickel and ammonium will begin to separate. The addition of am- monium sulphate should be continued from time to time until the liquid is colorless. The precipitated salt is very pure, and may be used directly in making a new bath. To improve defective nickeling. With the basis-metal thor- oughly cleansed defective places should not occur, but when they happen, by accident or negligence, recourse is to had to "doctoring." The " doctor" is arranged as follows : A piece of stout copper wire is bent in the form of a hook at each end, and a fragment of nickel anode is fastened firmly to one of the hooks with a piece of twine. The fragment of anode is then wrapped in several folds of muslin, the second hook connected by a wire to the anode-rod of the bath, and the article put in contact with the negative electrode. The rag end is now dipped in the nickel bath, applied to the defective spot, and allowed to rest upon it for a few moments, then dipped again and reap- plied. By repeatedly dipping the rag in the nickel bath and applying it in this way a sufficient coating of nickel may be given in a few minutes ; and if the operation is skillfully per- formed, no trace of the patch will be observable after polishing. Nickeling by contact and boiling. Franz Stolba has described a nickeling process by contact, which is executed as follows : In a bright copper kettle heat to boiling a concentrated solu- tion of zinc chloride with an equal or double the volume of soft water, and then add drop by drop pure hydrochloric acid until the precipitate formed by diluting the zinc chloride solution with water disappears. Then add as much zinc powder as will lie upon the point of a knife, the effect of this addition being 2l8 ELECTRO-DEPOSITION OF METALS. that the copper of the kettle as far as it comes in contact with the solution is in a few minutes zincked. Now bring into the kettle sufficient nickel salt, best nickel sulphate, to color the fluid perceptibly green ; then introduce the articles to be nick- eled together with small pieces .of sheet zinc or zinc wire, so as to present many points of contact, and continue boiling. With a correct execution of the process it is claimed the articles will be uniformly nickeled in 15 minutes; if such is not the case, the boiling must be continued, fresh pieces of zinc added, or, if the solution does not appear sufficiently green, fresh nickel salt introduced. For the success of the process "several conditions are neces- sary. The metallic articles must be thoroughly free from grease, as otherwise no deposit of nicfcel is formed on the greasy places. In boiling, the solution must not become turbid by the separation of basic zinc salt, nor acid by free hydrochloric acid, otherwise the nickeling will be duJl and blackish. Hence, any turbidity must be at once removed by adding drop by drop hydrochloric acid, and too great acidity by the careful addition of solution of carbonate of soda. The articles thus nickeled are to be thoroughly washed with water, dried, and polished with whiting. Since stains are readily formed by this process, especially when nickeling polished iron and steel articles, on the places where the metal to be nickeled comes in contact with the zinc, Stolba in later experiments omitted the zinc, and thus the con- tact process becomes a boiling process. To a 10 per cent, solution of zinc chloride add enough nickel sulphate to give the solution a deep green color and then heat, best in a porcelain vessel, to the boiling-point. Then without troubling about the turbidity of the bath caused by the separation of a basic zinc salt, immerse the objects, previously cleansed and freed from grease, in it in such a way that they do not touch each other, or at least in only a few places, and keep the whole boiling 30 to 60 minutes, from time to time replacing the water lost by evaporation. The after-treatment is the same as given above DEPOSITION OF NICKEL AND COBALT. 2IQ for the contact process ; the deposit of nickel is, of course, very thin. This process, while suitable for the amateur, cannot be rec- ommended to the professional electro-plater, the results not being sufficiently sure. A thin deposit of nickel of a light color may be obtained upon brass articles, but that upon iron articles is dark and mostly stained. Small articles, which are not to be nickeled by the battery, are preferably coated by contact with cobalt by the process to be described later on, under " Electro-cobalting." The higher price of cobalt salts makes little difference, small quantities only being required, and the color of cobalt can scarcely be distin- guished from that of nickel. By boiling a solution of 8j^ ozs. of nickel-ammonium sulphate and Sj/2 ozs. of ammonium chloride in I quart of water*, together with clean iron filings free from grease, and introducing into the fluid copper or brass articles, the latter become coated with a thin layer of nickel capable of bearing light polishing. The nickel solution has to be frequently renewed. According to R. Kaiser, an alloy containing nickel may be deposited upon articles by proceeding as follows : Melt I part of copper and 5 of tin, and granulate the fused mass by pouring it through a heated sheet-iron sieve into a bucket filled with water. Boil the granulated metal thus obtained with tartar free from lime, and add for every 100 parts by weight of granulated metal 0.5 part of glowed nickel oxide. Then bring the brass or copper articles, previously freed from grease and pickled, into the boiling fluid, and after boiling for a short time they will ap- pear coated with a white alloy resembling German silver. The addition of nickel oxide must be repeated from time to time. Iron and steel articles are to be previously coppered. By add- ing nickel carbonate to this bath, it is claimed, coats richer in nickel and of a darker color than that of platinum to blue-black are obtained. Deposits of nickel alloys. From suitable solutions of the metallic salts nickel may be deposited together with copper and 220 ELECTRO- DEPOSITION OF METALS. tin, as well as with copper and zinc. With the first combina- tion, especially, all tones from copper-red to gold-shade may be obtained, according to which metal predominates, or according to the current-strength which is conducted into the bath, as is also the case in brassing. A suitable bath for coating metallic articles with an alloy of nickel, copper, and tin, for which the term nickel- bronze is pro- posed, is obtained by dissolving the metallic phosphates in sodium pyrophosphate solution. By mixing solution of blue vitriol with solution of sodium phosphate, cupric phosphate is precipitated which is filtered off and washed. In the same manner nickel phosphate is prepared from a solution of nickel- sulphate. These phosphates are then, each by itself, dissolved in a concentrated solution of sodium pyrophosphate, while chloride of tin is directly dissolved in sodium pyrophosphate until the turbidity, at first rapidly disappearing, disappears but slowly. Nothing definite can be said in regard to the mixing propor- tions of these three solutions, because the proportions will have to be varied according to the desired color of the deposit ; the operator, however, will soon find out of which solution more must be added in order to obtain the tone desired. For depositing an alloy of nickel, copper, and zinc, solutions of cupric sulphate (blue vitriol) and zinc white in potassium cyanide, to which is added an ammoniacal solution of nickel carbonate, may be advantageously used. According to a French process, a deposit of German silver may be obtained as follows : Dissolve a good quality of German 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, dissolved 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 combi- nation. Watt recommends the following method : Cut up into small DEPOSITION OF NICKEL AND COBALT. 221 pieces sheet German silver about I oz., place the strips in a glass flask, and add nitric acid diluted with an equal bulk of water. Assist the solution of the metal by gentle heat. When red fumes cease to appear in the bulb of the flask, decant the liquor and apply fresh acid, diluted as before, to the undissolved metal, taking care to avoid excess ; it is best to leave a small quantity of undissolved metal in the flask, by which an excess of acid is readily avoided. The several portions of the metallic solutions are to be mixed and diluted with about 3 pints of cold water in a gallon vessel. Next dissolve about 4 ozs. of car- bonate of potash in a pint of water, and add this gradually to the former, with gentle stirring, until no further precipitation takes place. The precipitate must be washed several times with hot water, and then redissolved by adding a strong solu- tion of cyanide, with stirring, and about I oz. of liquid am- monia. To avoid adding too great an excess of cyanide, it is a good plan, when the precipitate is nearly all dissolved, to let it rest for half an hour or so, then decant the clear liquor, and dissolve the remainder of the precipitate separately. A small excess of cyanide solution may be added as " free cyanide," and the whole mixed together and made up to one gallon with cold water. The solution should then be filtered or allowed to repose for about 12 hours, and the clear liquor then carefully decanted from any sediment which may be present from cyanide impurities. The bath must be worked with a German-silver anode, which should be of the same quality as that from which the solution is prepared ; a Bunsen battery should be employed as the source of electricity, or a dynamo-machine. 2. Cobalting. Properties of cobalt. Cobalt has nearly the same color as nickel, with a slightly reddish tinge ; its specific gravity is 8.56. It is< exceedingly hard, highly malleable and ductile, and capa- ble of taking a polish. It is slightly magnetic, and preserves this property even when alloyed with mercury. It is rapidly dissolved by nitric acid, and slowly by dilute sulphuric and hydrochloric acids. 222 ELECTRO-DEPOSITION OF METALS. For cobalting, the baths given under nickeling may be used by substituting for the nickel salt a corresponding quantity of cobalt salt. By observing the rules given for 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 practised. On account of the greater solubility of cobalt in dilute sulphuric acid it is, however, under all circumstances, to be preferred for facing valuable cop- per plates for printing. According to the more or less careful adjustment of such plates in the press, many places of the facing are more or less attacked, and it may be desired to remove the coating and make a fresh deposit. For this purpose, Gaifife has proposed the use of cobalt in place of nickel, because the former dissolves slowly but completely in dilute sulphuric acid. He recommends a solution of i part of chloride of cobalt in 10 of water. The so- lution is to be neutralized with aqua ammonia, and the plates are to be electro-plated with the use of a moderate current. Cobalt precipitated from its chloride solution does not how- ever yield a hard coating, and hence the following bath is recom- mended for the purpose : Double sulphate of cobalt and am- monium 21 ozs., cobaltous carbonate 0.8 oz.. crystallized boric acid 10^ ozs., water 10 quarts. The bath is prepared in the same manner as No. VII., given under "Nickeling." It requires a tension of 2.5 to 2.75 volts. To determine whether and how much copper is dissolved in stripping the cobalt deposit from cobalted copper plates, a cop- per plate with a surface of 7^ square inches was coated with 7.71 grains of cobalt and placed in dilute sulphuric acid (i part acid of 66 Be., to 12.5 parts of water). After the acid had acted for 1 6 hours, the cobalt deposit was partially dissolved and had partially collected in lamina 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 P er cent., this loss being apparently chiefly from the back of the plate, the engraved DEPOSITION OF NICKEL AND COBALT. 223 side exhibiting no trace of corrosion. This experiment proved that there is no danger of destroying the copper plate by strip- ping the cobalt deposit with dilute sulphuric acid, provided the operation is executed with due care and attention. Warren has described a cobalt solution which can be de- composed in a single cell apparatus, and for this reason would seem suitable for electro-plating small articles en masse. 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 voluminous precipitate at first formed is almost entirely redissolved, and then filter. Bring the bath into a vessel and place the latter in a clay cell filled with concentrated solution of sal ammoniac 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 current the objects become gradually coated with a lustrous cobalt deposit which, after 2 hours, is sufficiently heavy to bear vigorous polishing with the bob. Zinc may be coated in the same manner. The following solution has been recommended by Mr. G. W. Beardslee, of Brooklyn, N. Y., and is claimed to yield a good deposit of cobalt which is very white, exceedingly hard, and tenaciously adherent: Dissolve pure cobalt in boiling hydro- choloric acid and evaporate the solution to dryness. Next dis- solve 4 to 6 ozs. of the resulting salt in I gallon of distilled water, to which add liquid ammonia until it turns red litmus- paper blue. The solution being thus rendered slightly alka- line, is ready for use. A battery power of from two to five Smee cells will be sufficient to do good work. Care must be had not to allow the solution to lose its slightly alkaline con- dition, upon which the whiteness, uniformity of deposit, and its adhesion to the basis-metal greatly depend. For cobalting small fancy articles of copper, brass, or steel, R. Daub recommends the following bath: Dissolve 4^ ozs. of double sulphate of cobalt and ammonium in 4^ quarts of 224 ELECTRO-DEPOSITION OF METALS. water. The solution should show, at 59 F., a specific gravity of 1.015. The most suitable current-strength is 0.8 ampere with about two volts. The size of the anodes is of great influ- ence as regards the uniformity of the cobalting. For the deposition of cobalt upen brass, copper, steel, or iron, the anodes may consist of rolled cobalt in strips about 2 inches wide and 10 to 12 inches long, according to the size of the arti- cles. The anodes are arranged on the sides of the vat, about 6 inches apart. With the use of a large vat holding from 500 to 1000 quarts of bath a corresponding series of such anodes are to be suspended to a conducting rod which rests length- wise upon the ends of the vat. The metallic articles should be coated with a thin film of cobalt in a few seconds after having been suspended in the bath, and the current strength is then reduced, to be increased only when more articles are brought into the bath. The mode of treatment is different from that in the nickel bath, and, since cobalt deposits with greater ease than nickel, the regulation of the current is the principal point. The current-strength should be reduced as soon as the articles are entirely and nicely coated with cobalt. Copper articles re- quire at the beginning a stronger current than brass objects, while for articles of iron or steel the current should be weaker than for either brass or copper. Places in relief should be kept as far as possible from the anodes to prevent blackening or burning. According to R. Daub, the principal condition for the success of the operation is to maintain a uniform density of the bath, either by the addition of water or of cobalt salt, as may be required. The color of the deposit is much influenced by the current-strength. Thus a deposit with I volt and a large anode-surface is not so white as one with two volts and a smaller anode-surface, about 2 /$ of that of the cathode. Cast- brass is especially suitable for cobalting, as well as metallic articles which are kept in dry rooms or used for ornamental purposes. Cobalting by contact. While nickeling by contact with zinc yields only incomplete results, the cobalting of copper and brass DEPOSITION OF COPPER, BRASS, AND BRONZE. 225 articles succeeds very well with the use of the following bath : Crystallized cobalt sulphate 0.35 oz., crystallized sal ammoniac 0.07 oz., water I quart. Heat the bath to between 104 and 122 F., and immerse the previously cleansed and pickled articles in the bath, bringing them in contact with a bright zinc surface not too small ; for small articles a zinc sieve may be used. In 3 or 4 minutes the coating is heavy enough to bear vigorous polishing. CHAPTER VIII. DEPOSITION OF COPPER, BRASS, AND BRONZE. i. COPPERING. Properties of copper. Copper has a characteristic red color, and possesses strong lustre ; it is very tenacious, may be rolled to thin lamina, and readily drawn into fine wire. The specific gravity of wrought copper is 8.95, and of cast 8.92. Copper fuses more readily than gold, but with greater difficulty than silver. In a humid atmosphere containing carbonic acid, copper be- comes gradually coated with a green deposit of basic carbonate ; when slightly heated it acquires a red coating of cuprous oxide, and when strongly heated a black coating of cupric oxide with some cuprous oxide. Copper is most readily attacked by nitric acid, but is slowly dissolved when immersed in heated hydro- chloric or sulphuric acid ; with exclusion of the air, it is not dissolved by dilute sulphuric or hydrochloric acid, and but slightly with admission of the air. Liquid ammonia causes a rapid oxidation of copper in the air and the formation of a blue solution. An excess of potassium cyanide dissolves copper. Sulphuretted hydrogen blackens bright copper. Copper baths. The composition of these baths depends on the purpose they are to serve, and below are mentioned the most approved baths, with the exception of the acid copper 15 226 ELECTRO-DEPOSITION OF METALS. bath used for plastic deposits of copper, which will be discussed later on under " Copper galvanoplasty." In most cases the more electro-positive metals, zinc, iron, tin, etc., are to be coppered either as preparation for the succeed- ing process of nickeling, silvering, or gilding, or to protect them against oxidation, or for the purpose of decoration. The above-mentioned electro-positive metals, however, decompose acid copper solutions and separate from them pulverulent cop- per, while an equivalent portion of zinc, iron, tin, etc., is dis- solved. For this reason, such solutions of copper cannot be used for coating these metals for this purpose, alkaline copper baths being exclusively employed, which may be arranged under two groups those containing potassium cyanide, and those without it. Hassauer prepares a copper bath by dissolving 3*^ ozs. of copper cyanide in a solution of i/j^ ozs. of 70 per cent, potassium cyanide in 3 quarts of water, boiling, filtering, and diluting with 7 quarts of water to a lo-quart bath. This bath works very well when heated to between 113 and 122 F., but when used cold requires a very strong current, and hence the use of the following formulae is recommended: Copper baths for iron and steel articles. I . To be used at the ordinary temperature. Water 10 quarts, bisulphite of soda in powder 7 ozs., crystallized carbonate of soda 14 ozs., neutral acetate of copper 7 ozs., 75 per cent, potassium cyanide 7 ozs., spirits of sal ammoniac 4.4 ozs. 1 1 , For hot coppering ( at between 140 and 158 F. ) Rose leu r recommends: Water 10 quarts, bisulphite of soda in powder 2 1 ozs., crystallized carbonate of soda 7 ozs., neutral acetate of copper 7 ozs., 75 per cent, cyanide of potassium 9| ozs., spirit of sal ammoniac 4 ozs. The baths are best prepared as follows : Dissolve the bisul- phite and carbonate of soda in one-half the water, the potassium cyanide in the other half, and mix the copper salt with the spirit of sal ammoniac ; then pour the blue ammoniacal copper solution into the solution of the soda salts, and finally add the DEPOSITION OF COPPER, BRASS, AND BRONZE. 227 potassium cyanide solution; the bath will then be clear and colorless. Boiling, though not absolutely necessary, is of ad- vantage, after which the solution is to be filtered. According to full investigations made, the excess of carbonate of soda in formula I. serves no special purpose, but on the contrary, in many cases, is directly detrimental ; neither is the use of ammonia of any special advantage, and it may just as well, or rather better, be omitted. Further, the use of separate baths for cold and warm coppering is at least questionable. It is believed that a single bath suffices for both cases, heating having been found of special advantage only for rapid and thick coppering, or for obtaining particular shades which are produced with difficulty in the cold bath, but without trouble in the heated bath. The following formula may be highly recommended, a cop- per bath composed according to it always yielding good and sure results : III. Water 10 quarts, crystallized carbonate of soda 8^ ozs., crystallized bisulphite of soda 7 ozs., neutral acetate of copper 7 ozs., 98 or 99 per cent, potassium cyanide 8^ ozs. The bath is prepared as follows : Dissolve in 7 quarts of warm water the carbonate of soda, gradually add the bisulphite of soda to prevent violent effervescence, and then add, with vigorous stirring, the acetate of copper in small portions. Dissolve the potassium cyanide in 3 quarts of cold water, and mix both solutions when the first is cold. By thorough stirring with a clean wooden stick a clear solution is quickly obtained which is allowed to settle and siphoned off clear. If after the addition of the potassium cyanide the bath should not become colorless, or at least wine-yellow, add a small quantity more of potassium cyanide. This bath does not require a strong cur- rent, and yields an especially heavy coppering of a beautiful red color; a current of 0.4 ampere at a tension of 3 to 3.5 volts is calculated for 15^ square inches of surface of objects. With a greater content of potassium cyanide the tension may be correspondingly decreased. 228 ELECTRO-DEPOSITION OF METALS. For coppering zinc articles, Roseleur recommends the follow- ing bath : IV. Water 10 quarts, tartar, free from lime, 6.7 ozs., crystal- lized carbonate of soda 15 ozs., blue vitriol 6.7 ozs., caustic soda lye of 16 Be. f Ib. To prepare this bath, dissolve the tartar and the crystallized carbonate of soda in ^ of the water, and the blue vitriol in the remaining J^, and mix both solutions. Filter off the precipi- tate, dissolve it in the caustic soda lye, and add this solution to the other. This bath works very well, and may be recommended to electro- platers who copper zinc exclusively, but where all kinds of metals are to be coppered, bath No. III. is to be preferred, it yielding equally good results for zinc. For small zinc objects which are to be coppered in a sieve, bath No. III. is used, it being heated for this purpose, and a little more potassium cyanide added. Roseleur recommends for the same purpose a bath composed as follows: V. Water 10 quarts, neutral crystallized bisulphite of soda i y ozs., neutral acetate of copper 8 ozs., 75 per cent, potass- ium cyanide I2j^ ozs., and ammonia y^ oz. The bath is pre- pared in the same manner as formulae I. to III. In preparing copper baths, the acetate of copper prescribed in the preceding formulae may be replaced by the carbonate or sulphate, the substitution of the latter, after its previous con- version into carbonate, being of special advantage in order not to impart to the bath too great a resistance by the potassium sulphate, formed by reciprocal decomposition. The following formula is especially suitable for the use of sulphate of copper (blue vitriol) : VI. Blue vitriol . . . .... 10^ ozs. Crystallized carbonate of soda . . Water . ^ .... . .10 quarts. Pulverized bisulphite of soda . . . 7 ozs. Crystallized carbonate of soda . .. . 8^ ozs. 98 to 99 per cent, potassium cyanide . 8}4 " DEPOSITION OF COPPER, BRASS, AND BRONZE. 229 First dissolve the ioj^ ozs. of blue vitriol and the 10% ozs. of crystallized carbonate of soda, each by itself, in hot water, and mix the two solutions ; allow the precipitate of carbonate of copper to settle, and pour off the supernatant clear fluid. Then pour upon the precipitate 5 quarts of water, add the bisulphite of soda, next the carbonate of soda, and mix this solution with the solution of the potassium cyanide in 5 quarts of water. The fluid rapidly becomes clear and colorless, when it is boiled and filtered. In a recent formula cuprous oxide, which is found in com- merce under the name of cupron, is used in place of cupric oxides. VII. Cupron 3^ ozs., 99 per cent, potassium cyanide 10^ ozs., pulverized bisulphite of soda lO^J ozs., water 15 quarts. Dissolve the potassium cyanide in one half the prescribed quantity of water (cold), then gradually stir in the cupron, and after the solution of the latter add the bisulphite of soda pre- viously dissolved in the other half of the water. In place of cupron, cuproso-cupric sulphite, an article patented in Germany, may be used. This salt dissolves in potassium cyanide without perceptible evolution of cyanogen, since it contains more than the sufficient quantity of sulphurous acid than is required for the reduction of the oxide salt present. The baths prepared with cuproso-cupric sulphite can be pre- pared more cheaply than baths with cupron. Suitable formulae for baths with cuproso-cupric sulphite are as follows : VIII. Ammonia-soda if ozs., 99 per cent, potassium cyanide 8^2 ozs., cuproso-cupric sulphite 4j^ ozs., water 10 quarts; or, IX. 60 per cent, potassium cyanide 14 ozs., cuproso-cupric sulphite 4*4 ozs., water 10 quarts. Dissolve the salts in the order given in 5 quarts of the water, stirring constantly, and then add the remaining 5 quarts of water. Of the many directions for copper baths without potassium cyanide, to which also belongs the bath prepared according to formula IV., and which have chiefly been proposed for copper- 230 ELECTRO-DEPOSITION OF METALS. ing cast and wrought iron, only a few need be mentioned as being actually available. Weil obtains a deposit of copper in a bath consisting of a solution of blue vitriol in an alkaline solution of tartrate of potas- sium or sodium. Such a bath is composed as follows: X. Water 10 quarts, potassium sodium tartrate (Rochelle salt) 53 ozs., blue vitriol 10^ ozs., 60 per cent, caustic soda 28 ozs. The chief purpose of the large content of caustic soda is to keep the tartrate of copper, which is almost insoluble in water, in solution. According to Weil, the coppering may be execu- ted in three different ways, as follows : The iron articles tied to zinc wires or in contact with zinc strips are brought into the bath ; the coppering thus taking place by contact. Or, porous clay cells are placed in the bath containing the articles ; these clay cells are filled with soda lye in which zinc plates connected with the object-rods are allowed to dip, the arrangement in this case forming an element with which, by the solution of the zinc in the soda lye, a current is produced, which effects the decomposition of the copper solu- tion and the deposition. When saturated with zinc the soda lye becomes ineffective, and, according to Weil, it may be re- generated by the addition of sodium sulphide, which separates the dissolved zinc as zinc sulphide. The third method of 'copper- ing consists in the use of the current of a battery or of a dynamo- machine, in which case copper anodes have, of course, to be employed. A copper bath recommened by Walenn is composed of a solution of equal parts of tartrate of ammonia and potassium cyanide, in which 3 to 5 per cent, of copper (in the form of blue vitriol or moist cupric hydrate) is dissolved. The bath is to be heated to about 140 F. Copper bath according to Pfanhauser. Dissolve 2 ^ ozs. of cyanide of copper, i^j drachms each of pure 100 per cent, potassium cyanide and crystallized sal ammoniac, and 5^ drachms of ammonia soda in I quart of lukewarm water, stirring constantly until all the salts are dissolved. DEPOSITION OF COPPER, BRASS, AND BRONZE. 231 The temperature of the bath should be between 68 and 77 F., and the strength of current 3 volts. Density of current 0.5 ampere. In case the bath should become poor in metal, cyanide of copper has to be added. When the copper anodes become coated with too great an abundance of green slime, which does not decrease during the night when the bath is not working, some potassium cyanide, about J^ drachm per quart, should be added. Gauduin's copper bath consists of a solution of oxalate of copper with oxalate of ammonia and free oxalic acid. Fon- taine asserts that the bath works well, when heated to between 140 and 150 F. Copper baths containing cyanide cannot be brought into pitched vats, vats of stoneware or enameled iron being used for smaller baths, and for larger, basins of brick set in cement, or iron reservoirs lined with ebonite. For large baths containing potassium cyanide wooden vats lined with lead can be used without disadvantage, since a slight coating of cyanide of lead, which may be formed upon the lead, is insoluble in potassium cyanide, and even if a small quantity of cyanide of lead would be dissolved in the bath by the presence of organic acids, a separation of lead besides copper upon the cathodes does not take place. Execution of coppering. The general rules given under nickel- ing, as regards the suitable composition of the bath, correct selection of anodes, careful scouring and pickling of the objects and proper current-strength also apply to coppering. Annealed sheets of pure copper with as large a surface as possible serve as anodes. In all baths containing cyanide the anodes become, in a comparatively short time, coated with a greenish slime consisting of a basic copper cyanide mostly soluble in excess of potassium cyanide. When a very thick formation of such slime takes place, potassium cyanide is want- ing, and has to be added. Other phenomena appearing in copper baths containing cyanide may as well here be men- tioned. Too large an excess of potassium cyanide causes a 232 ELECTRO-DEPOSITION OF METALS. strong evolution of hydrogen bubbles on the objects ; but no deposition of copper, or only a slight one, takes place, which besides has the tendency to peel off. If this phenomenon ap- pears after adding potassium cyanide, the excess can be readily removed by the addition of copper salt, best cyanide of copper, stirred with a small quantity of the bath to a thinly fluid paste and added to the bath with constant and long-continued stirring. After each addition, a test is made whether an object suspended in the bath is rapidly and regularly coppered ; if such is not the case, the addition of cyanide of copper is repeated until the bath works in a faultless and correct manner. On the other Kand, a deposit may not be formed for the want of potassium cyanide, which is already indicated by a thick formation of slime on the anodes, and by the fluid acquiring a pale blue color; or the metallic content of the bath may be too small. While in the first case a slight addition of potassium cyanide alone will cause the bath to work correctly, in the other case, an addition of solution of copper cyanide in potassium cyanide is required to augment the content of metal in the bath, it being best to introduce together with the metallic cyanide solution a small quantity of carbonate and bisulphite of soda, in order to de- crease the resistance to conductivity. In place of solution of copper cyanide in potassium cyanide, commercial crystallized potassium copper cyanide may be used. In coppering with a strong current the anodes become frequently coated to such an extent that finally no current passes into the bath, the ex- cess of potassium cyanide being unable to dissolve the copper cyanide as rapidly as it is formed. In this case scouring the anodes is the only remedy. Many platers are of the opinion that the articles to be coppered do not require very careful cleaning and pickling be- fore plating because the copper bath containing potassium cyrnide as well as copper baths with alkaline-organic combina- tions sufficiently effect the cleansing and pickling. This opin- ion, however, is wrong. It is true the potassium cyanide dis- solves a layer of oxide, but not or at least very incompletely DEPOSITION OF COPPER, BRASS, AND BRONZE. 233 any grease present upon the articles, and hence it advisable to free articles intended for coppering as thoroughly from grease as articles to be nickeled. The preliminary scouring and pickling of the articles to be coppered are executed according to the directions given on page 156. The same precautions discussed under nickeling have to be used in suspending the objects in the bath, and the directions given there for the suitable arrangement of the anodes, etc., also apply to coppering; however, a copper bath conducting better than a nickel bath, the distance between the anodes and the objects may, if necessary, be somewhat greater. With a proper arrangement of the anodes and correct regu- lation of the current, the objects should be entirely coated with copper in a few minutes after being hung in the bath. In five to ten minutes the objects are taken from the bath and brushed with a scratch-brush of not too hard brass wires, whereby the deposit should everywhere show itself to be durable and ad- herent. Defective places are especially thoroughly scratch- brushed, scoured, and pickled ; the objects are then returned to the bath. For solid and heavy coppering the objects remain in the bath until the original lustre and red tone of the copper- ing disappear and pass into a dull discolored brown ; at this stage the objects are again scratch-brushed until they show lustre and the red copper color, whereby it is of advantage to moisten them with tartar water. They are then again returned to the bath, where they remain until the dull discolored tone reappears. They are then taken out, scratch-brushed bright, rinsed in several clean waters, plunged into hot water, and finally dried, first in sawdust and then thoroughly, at a high tempera- ture, in the drying chamber. Special attention must be paid to the thorough washing of the coppered objects, because, if any- thing of the bath containing cyanide remains in the depressions or pores, small, dark, round stains appear on those places, which cannot be removed, or at least only with great difficulty, they reappearing again in a short time after having been ap- parently removed. This formation of stains appears especially 234 ELECTRO- DEPOSITION OF METALS. frequently upon coppered (as well as brassed) iron and zinc castings, which cannot be produced without pores. To prevent the formation of these stains the following method is recom- mended : Since the rinsing in many waters, and even allowing the objects to lie for hours in running water, offer no guarantee that every trace of fluid containing cyanide has been removed, the objects are brought into a slightly acid bath which de- composes the fluid, a mixture of I part of acetic acid and 50 parts of water being well adapted for the purpose. The objects are allowed to remain in this mixture for three to five minutes, when they are rinsed off in water and dipped for a few minutes in dilute milk of lime. They are finally rinsed off and dried. Coppered castings thus treated will show no stains. O. Shultz obtained a patent for the following method for re- moving the hydrochloric acid from the pores, and thus prevent- ing the formation of stains : The plated objects are placed in a room which can be hermetically closed. The air is then re- moved from the room by the introduction of steam of a high tension, and by means of an air-pump, and water sprinkled upon the objects. By this treatment in vacuum the fluid in the pores comes to the surface and the salt solution is removed by the water sprinkled over the articles. After drying, the deposit of copper, if it is to show high lustre, is polished with soft wheels of fine flannel and dry Vienna lime ; commercial polishing red FFF, moistened with a little alcohol, is also an excellent polishing agent for copper and all other soft metals. As is well known, massive copper rapidly oxidizes in a humid atmosphere, and this is the case to a still greater extent with electro-deposited copper. Hence, the coppered objects, if they are not to be further coated with a non-oxidizing metal, have to be provided with a colorless, transparent coat of lacquer (see " Lacquering"). It frequently happens that slightly coppered (as well as slightly brassed) objects, especially of zinc, after some time, be- come entirely white and show no trace of the deposit. This is DEPOSITION OF COPPER, BRASS, AND BRONZE. 235 due to the deposit penetrating into the basis-metal, as already explained. Lacquering in this case is of no avail, the deposit also disappearing under the coat of lacquer. The only remedy against this phenomenon is a heavier deposit. If the coppered objects are to be coated with another metal, drying is omitted, and after careful rinsing they are directly brought into the respective bath, or into thequicking pickle, if, as, for instance, in silvering, quicking has to be done. In such cases, where the copper deposit serves only as an intermediary for the reception of another metallic coating, the objects need not to be coppered as thickly, as previously described, by treating them three times in the bath. Preliminary coppering for 5 to 10 minutes suffices in all cases, which is succeeded by scratch- brushing in order to be convinced that the deposit adheres firmly and that the basis-metal is uniformly coated. The ob- jects are then hung in the bath for 5 to 10 minutes longer with a weak current. In coppering sheet iron or sheet zinc which is to be nickeled, the sheets are taken from the bath after 3 to 5 minutes, at any rate while they still retain their lustre, scratch- brushing being in this case omitted. For coppering such sheets a current-density of 0.5 ampere with a tension of 3.5 to 4 volts is required. The treatment of copper baths, when they be- come inactive or exhibit other abnormal phenomena, has been referred to on p. 194; all other rules for galvanic baths given in Chap. VI. must here also be observed. For coppering small articles en masse in sieves it is recom- mended to have the copper baths right hot ; for the rest, the process is the same as that given for nickeling small articles en masse. Coppering by contact arid 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 Ibs. 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 decom- 236 ELECTRO-DEPOSITION OF METALS. position of the carbonate of copper ceases, and then add in small portions, and with constant stirring, pure whiting until effervescence is no longer perceptible. Filter off the fluid from the tartrate of lime, separate and wash the precipitate so that the filtrate, inclusive of the wash water, amounts to 10 or 12 quarts. Zinc is coppered in this bath by simple immersion ; other metals have to be brought in contact with zinc. To coat zinc plates with a very thin but hard layer of copper, immerse the plates in a bath composed of 100 parts of water saturated with cupric chloride cupric chloride 40 parts, water 60 150 parts of ammonia and 3000 parts of water. For very solid coppering, the above-described bath, which is of a beautiful blue color, is used, and a saturated solution of potassium cyanide in water added until the blue of the first mixture has quite disappeared. For plates engraved with the burin or for stamped plates, it is best to use a mixture of cyanide of copper with neutral potassium sulphate, to which is added a mixture of a saturated solution of blue vitriol in water and of water satur- ated with cyanide of copper. The bath is ready for use when the precipitate is completely dissolved and the fluid entirely discolored. Another contact coppering bath is that prepared according to formula X., proposed by Weil. In this bath zinc is also coppered by simple immersion, and copper and iron in con- tact with zinc strips. According to Bacco, a copper bath in which zinc may be coppered by immersion, and iron and other metals in contact with zinc, is prepared by adding to a saturated solution of blue vitriol, potassium cyanide solution until the precipitate of cyanide of copper which is formed is again dissolved. Then add T V to \ of the volume of liquid ammonia and dilute with water to 8 Be. The so-called brush-coppering which has been recommended may here be mentioned. This process may be of practical advantage for coppering very large objects which by another DEPOSITION OF COPPER, BRASS, AND BRONZE. 237 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 application. One of the vessels contains a strongly satu- rated solution of caustic soda, and the other a strongly satu- rated 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 deposited upon the object. Care must be had not to have the brush too full and not to touch the places once gone over the second time, as otherwise the layer of copper does not adhere firmly. Many iron and steel objects are provided with a thin film of copper in order to give them a more pleasing appearance. For this purpose a copper solution of 10 quarts of water, I ^ ozs. of blue vitriol, and I ^ ozs. of pure concentrated sulphuric acid may be used. Dip the iron or steel objects, previously freed from grease and oxide, for a moment in the solution, moving them constantly to and fro ; then rinse them immediately in ample water, and dry. By keeping the articles too long in the solution, the copper separates in a pulverulent form and does not adhere. Steel pens, needles' eyes, etc., may be coppered by diluting the copper solution just mentioned with double the quantity of water, moistening sawdust with the solution and revolving the latter, together with the articles to be coppered, in a wooden tumbling box (p. 129). The inlaying of depressions of coppered art-castings with black may be done in different ways. Some blacken the ground by applying a mixture of spirit lacquer with lampblack and graphite, while others use oil of turpentine with lampblack and a few drops of copal lacquer. A very thin nigrosin lacquer mixed with finely pulverized graphite is very suitable for the purpose. When the lacquer is dry the elevated places which 238 ELECTRO-DEPOSITION OF METALS. are to show the copper color are cleansed with a linen rag moistened with alcohol. Electrolytically coppered articles may be inlaid black by coating them, after thorough scouring and pickling, with arsenic in one of the baths given under " Electro-deposition of Arsenic," and, after drying in hot water and sawdust, freeing the surfaces and profiles, which are to appear coppered, from the coating of arsenic by polishing upon a felt wheel. If this polishing is to be avoided, the portions which are not to be black may be coated with stopping-off varnish, and arsenic deposited upon the places remaining free. For coloring, platinizing, and oxidizing of copper, see the proper chapter. 2. Brassing ( Cuivre-poli Deposit) . Brass is an alloy of copper and zinc whose color depends on the quantitative proportions of both metals. The alloys known as yellow brass ', red brass (similor, tombac}, consist essentially of copper and zinc, while those known as bell metal, gun metal, and the bronzes of the ancients are composed of copper and tin. Modern bronzes contain copper, zinc, and tin. The behavior of brass towards acids is nearly the same as that of copper ; 'it oxidizes, however, less readily in the air, is harder than copper, malleable, and can be rolled and drawn into wire. Brass baths. According to the plan pursued in this work, only the most approved formulae will be given. There exist a large number of directions for brass baths ; but we share the opinion of Roseleur, that a brass bath containing copper and zinc salts in nearly equal proportions is the most suitable and least subject to disturbances. A brass bath is to be considered as a mixture of solutions of cyanide of copper and cyanide of zinc, or of other copper- zinc salts in the most suitable solvent; and since a solution of cyanide of copper requires a different current- strength from one of zinc salt, it will be seen that according to the greater or smaller current-strength, now more of the one, DEPOSITION OF COPPER, BRASS, AND BRONZE. 239 and now more of the other metal is deposited, which, of course, influences the color of the deposit. Hence the proper regula- tion of the current is the chief condition for obtaining beauti- ful deposits, let the bath be composed as it may. For all baths containing more than one metal in solution, it may be laid down as a rule that the less positive metal is first deposited. In a brass bath copper is the negative and zinc the positive metal ; and hence a weaker current deposits more copper, in consequence of which the deposit becomes redder, while, vice versa, a more powerful current decomposes besides the copper solution also a larger quantity of zinc solution and reduces zinc, the color produced being more pale yellow to greenish. By bearing this in mind it is not difficult to ob- tain any desired shades within certain limits. I. Brass bath according to Roselenr. Blue vitriol and zinc sulphate (white vitriol), of each 5^ ounces, and crystallized carbonate of soda 15^ ounces. Crystallized carbonate of soda and crystallized bisulphite of soda, of each 7 ounces, 98 per cent, potassium cyanide 8^ ounces, arsenious acid 30^ grains, water 10 quarts. The bath is prepared as follows : In 5 quarts of warm water dissolve the blue vitriol and the zinc sulphate ; and in the other 5 quarts the 15^ ounces of carbonate of soda; then mix both solutions, with stirring. A precipitate of carbonate of copper and carbonate of zinc is formed, which is allowed quietly to settle for i o to 12 hours, when the supernatant clear fluid is carefully poured off, so that nothing of the precipitate is lost. Washing the precipitate is not necessary ; the clear fluid poured off is of no value and is thrown away. Now add to the preci- pitate so much water that the resulting fluid amounts to about 6 quarts, and dissolve in it, with constant stirring, the carbonate and bisulphite of soda, adding these salts, however, not at once, but gradually, in small portions, to avoid foaming over by the escaping carbonic acid. Dissolve the potassium cyanide in 4 quarts of cold water and add this solution, with the exception of about y?, pint, in which the arsenious acid is dissolved with 240 ELECTRO- DEPOSITION OF METALS. the assistance of heat, to the first solutions, and finally add the solution of arsenious acid in the j pint of water retained, when the bath should be clear and colorless. If after continued stir- ring, particles of the precipitate remain undissolved, carefully add somewhat more potassium cyanide until solution is com- plete. Fresh brass baths work, as a rule, more irregularly than any other baths containing cyanide, the deposit being either too red or too green or gray, while frequently one side of the object is coated quite well, and the other not at all. To force the bath to work correctly it must be thoroughly boiled, the water which is lost by evaporation being replaced by the addition of dis- tilled water or pure rain water. If boiling is to be avoided, the bath, as previously mentioned, is worked through for hours, and even for days, with the current, until an object suspended in it is correctly brassed. The addition of a small quantity of arsenious acid is claimed to make the brassing brighter ; but the above mentioned pro- portion of 30^ grains for a lO-quart bath must not be ex- ceeded, as otherwise the color of the deposit would be too light and show a gray tone. II. Crystallized carbonate of soda 10^ ounces, crystallized bisulphite of soda 7 ounces, neutral acetate of copper 4.4 ounces, crystallized chloride of zinc 4.4 ounces, 98 per cent, potassium cyanide 14.11 ounces, arsenious acid 30^ grains, water 10 quarts. The preparation of this bath is more simple than that of the preceding. Dissolve the carbonate and bisulphite of soda in 4 quarts of water, then mix the acetate of copper and chloride of zinc with 2 quarts of water, and gradually add this mixture to the solu- tion of the soda salts. Next dissolve the potassium cyanide in 4 quarts of water, and add this solution to the first, retaining, however, a small portion of it, in which dissolve the arsenious acid with the assistance of heat. Finally add the arsenious acid solution, when the bath will become clear. Boiling the bath, or working it through with the current, is also required. DEPOSITION OF COPPER, BRASS, AND BRONZE. 241 For brassing iron in this bath the addition of carbonate of soda may be increased up to 35 ounces for a lo-quart bath, this being also permissible when frequent scratch-brushing is to be avoided in coating zinc articles with a heavy deposit of brass ; because it seems that a large content of carbonate of soda in the bath considerably retards the changing of the brass color into a discolored brown, though the brilliancy of the de- posit appears to suffer somewhat. When boiled from I to 2 hours, or worked through with the current for 10 to 12 hours, the bath prepared according to formula II. works very well ; it requires a current of 0.5 to 0.55 ampere, with a tension of 3.5 to 4 volts per I$j4 square inches surface. The same as for copper baths, cuproso-cupric sulphite may also be advantageously used for the preparation of brass baths, a suitable formula being as follows : III. Pure crystallized sulphate of zinc (zinc vitriol or white vitriol) 5 ^ ozs., crystallized carbonate of soda 7 ^ ozs. Neutral crystallized bisulphite of soda 9^ ozs., ammonia-soda \y 2 ozs., 99 per cent, potassium cyanide 3 ozs., cuproso-cupric sulphite 3 ozs., water 10 quarts. The bath is prepared as follows : Dissolve the sulphate of zinc in 5 quarts of the water, the carbonate of soda in 4 quarts of warm water, and mix the two solutions. After complete settling of the precipitate of carbonate of zinc formed, siphon off the supernatant clear fluid as much as possible, add 5 quarts of water and then the ammonia-soda. In the other 5 quarts of water dissolve the potassium cyanide and the neutral bisulphite of soda, and when solution is complete add this solution to the first, when by vigorous stirring the carbonate of zinc will also dissolve. This bath yields beautiful pale yellow deposits of a warm brass tone. IV. Crystallized carbonate of soda 10^ ozs., crystallized bisulphite of soda 7 ozs., cyanide of copper and cyanide of zinc of each 3J^ ozs., water 10 quarts, and enough 98 per cent, potassium cyanide to render the solution clear. 16 242 ELECTRO-DEPOSITION OF METALS. To prepare the bath dissolve the carbonate and bisulphite of soda in 2 to 3 quarts of water, rub in a porcelain mortar the cyanide of copper and cyanide of zinc with a quart of water to a thin paste, add this paste to the solution of the soda salts, and finally add, with vigorous stirring, concentrated potassium cyan- ide solution until the metallic cyanides are dissolved. Dilute the volume to 10 quarts, and, for the rest, proceed as given for formulae I. and II. For brassing zinc exclusively, Roseleur recommends the fol- lowing bath : V. Dissolve 9^ ozs. of crystallized bisulphite of soda and 14 ozs. of 70 per cent, potassium cyanide in 8 quarts of water, and add to this solution one of 4^ ozs. each of neutral acetate of copper and crystallized chloride of zinc, 5^ ozs. of aqua ammonia, and 2 quarts of water. For brassing cast-iron, wr ought-iron, and steel, Gore highly recommends the following composition: VI. Dissolve 35 ^ ozs. of crystallized carbonate of soda, 7 ozs. of crystallized bisulphite of soda, 13^ ozs. of 98 per cent, potassium cyanide in 8 quarts of water; then add, with con- stant stirring, a solution of fused chloride of tin 3^ ozs., and neutral acetate of copper 4^ ozs., in 2 quarts of water. Boil and filter. This bath works best with a current of 3.75 volts. According to Norris and Johnson, a good brass bath is said to be obtained as follows : VII. Carbonate of ammonia 35 J^ ozs., 70 per cent, potassium cyanide 35 ]/^ ozs., cyanide of copper and cyanide of zinc, each 2j{ ozs., water 10 quarts. The large content of potassium cyanide in this bath is unin- telligible. A solution for transferring any copper- zinc alloy serving as anode is composed, according to Hess, as follows: VIII. Bisulphite of soda 14^ ozs., crystallized sal ammoniac 9*4 ozs., 98 per cent, potassium cyanide 2^/2 ozs., water 10 quarts. Cast metal plates are to be used as anodes. The transfer DEPOSITION OF COPPER, BRASS, AND BRONZE. 243 begins after a medium strong current has, for a few hours, passed through the bath. This bath is also well adapted for the deposition of tombac, with the use of tombac anodes ; and the most suitable tension of the current is 3 to 3.5 volts. IX. For brassing all kinds of metals Wm. Pfanhauser, of Vienna, recommends the following bath: Dissolve 1 1/2, ozs. each of cyanide of copper and cyanide of zinc, 1 1/6 drachms of pure looper cent, potassium cyanide, i l /& drachms of crystallized sal ammoniac, and 5 */ 2 drachms of am- monia-soda in I quart of lukewarm water, stirring constantly until all the salts are dissolved. The bath is ready for imme- diate use, and does not requfre boiling or previous working through with the current. The temperature of the bath should be between 68 and 77 F. For brassing zinc the current should have a strength of 2^ volts, for iron 3 volts, for chains 3 to 3^ volts, and for small articles en masse 4 volts. Density of the current, 0.5 ampere. From the composition of this bath it will be seen that it con- tains quite a large content of metal, i^ ozs. of cyanide of copper being equal to about 6^ drachms of copper, and \y 2 ozs. of cyanide of zinc to about 5j drachms of zinc. Hence the bath contains about 12*^ drachms of brass per quart. Brassing in this bath succeeds equally well with all kinds of metals, the result being a uniform deposit of metal while the color, even of thick deposits, is a fiery sad yellow. Small articles, which are suspended en masse in dipping baskets, as well as steel chains, and even cast-iron, which is notoriously difficult to brass, become rapidly coated in this bath. In case the brass anodes become coated with too great an abundance of green slime, which decreases during the night when the bath is not working, some potassium cyanide, about I J^ drachms per quart, should be added. Of course, the bath must be supplied from time to time with additions of fresh cyanide of copper and cyanide of zinc. Execution of brassing. The most suitable density of current for brassing is 0.6 to 0.7 ampere at 3 to 4 volts. 244 ELECTRO-DEPOSITION OF METALS. As previously mentioned, the color of the deposits depends on the proportional quantity in which copper and zinc are present, a strong current depositing more zinc and a weak cur- rent more copper. By diminishing or increasing the current- strength by means of the resistance board, a deposit of a redder or more pale yellow to greenish color can be produced. How- ever, with a bath which does not contain copper and zinc in the correct proportional quantities, and especially with old baths long in use, a determined color of the deposit cannot be produced with the assistance of the resistance board. In such case the content of the metal lacking in the bath, which is re- quired for the production of a determined color, must be aug- mented by the addition of solution of the respective metallic salt in potassium cyanide. Suppose a bath which originally contained copper and zinc salts in equal proportions has been long in daily use. Now, since brass contains more copper than zinc, it is evident that more of the former will be withdrawn from the bath than of the latter, and finally a limit will be reached when the bath with a current suitable for the decomposition of the solution will deposit a greenish or gray brass, and with a weaker current produce no deposit whatever. The only help in such a case is the addition of sufficient solution of cyanide of copper in potassium cyanide, so that, even with quite a powerful current, a deposit of a beautiful brass color is produced, the shades of which can then again be controlled with the help of the resistance board. However, it must not be forgotten that every addition of a metallic salt momentarily irritates the brass bath, making it, so to say, sick, and to confine this phenomenon to the narrowest limit, an addition of carbonate and bisulphite of soda should at the same time be made, and the bath be worked through with the current as previously described, until a test shows that it works in a regular manner. Annealed sheets of brass not rolled too hard, and of as nearly as possible the same composition and color the deposit is to show, are used as anodes. The anode-surface should be at DEPOSITION OF COPPER, BRASS, AND BRONZE. 245 least twice as large as that of the objects to be brassed, though it is best to use as many anodes as the anode-rods will hold. As in the copper bath, an abundant formation of slime on the anodes indicates the want of potassium cyanide in the bath. In this case the evolution of gas bubbles on the objects is very slight, and the deposit forms slowly. This is remedied by an addition of potassium cyanide. The slow formation of the de- posit, however, may also be due to a want of metallic salts ; in this case not only potassium cyanide, but also solution of cyanide of copper and cyanide of zinc in potassium cyanide, has to be added. For this purpose prepare a concentrated solution of potassium cyanide in water, and a solution of equal parts of blue vitriol and zinc sulphate in water. From the latter precipitate the copper and zinc as carbonates with a solution of carbonate of soda, as given in formula I., p. 239. After allowing the precipitate to settle, pour off the clear supernatant fluid and add to the precipitate, with vigorous stirring, of the potassium cyanide solution, until it is dissolved ; if heating takes place thereby, add from time to time a little cold water. Add this solution with a small excess of potassium cyanide, and the addition of carbonate or bisulphite of soda, to the bath, and boil the latter or work it through with the current. A more simple method is to procure cyanide of copper and cyanide of zinc, or concentrated solutions of these combina- tions, from a dealer in such articles. In the first case rub in a mortar equal parts of cyanide of zinc and cyanide of copper with water to a thickly fluid paste. Pour this paste into potas- sium cyanide solution, containing about 7 ozs. of potassium cyanide to the quart, as long as the metallic cyanides dissolve quite rapidly with stirring. When solution takes place but slowly, stop the addition of paste. When a brass bath contains too large an excess of potassium cyanide, a very vigorous evolution of gas takes place on the objects, but the deposit is formed slowly or not at all ; besides, the deposit formed has a tendency to peel off in scratch-brush- ing. In this case the injurious excess has to be removed, which 246 ELECTRO-DEPOSITION OF METALS. is effected by pouring, with vigorous stirring, a quantity of the above-mentioned thinly fluid paste of cyanide of zinc and of copper into the bath. To avoid unnecessary repetition we refer, as regards the pro- duction of thick deposits, scatch-brushing and polishing of the plated articles, to what has been said under " Execution of Coppering," the directions given there being also valid for brassing. The deposition of several metals from a common solution is not an easy task, and requires attention and experience; if, however, the directions given in this chapter are followed, the operator will be able to conduct, after short experience, the brassing process with the same success as one in which but one metal is deposited. In brassing, the distance of the objects to be brassed from the anodes is of considerable importance. If objects with deep depressions or high reliefs are hung in the brass bath, it will be found that, with the customary distance of 3 ^ to 5 ^ inches from the anodes, the brassing of the portions in relief nearest to the anodes will turn out of a lighter color than that of the de- pressed portions, which will show a redder deposit, the reason for this being that the current acts more strongly upon the portions in relief, and consequently deposits more zinc than the weaker current, which strikes the depressions. To equalize the difference, the objects have to be correspondingly further re- moved from the anodes, with lamp-feet up to 9^ inches, and even more, when a deposit of the same color will be every- where formed. The brassing of unground iron-castings is especially trouble- some, and in order to obtain a beautiful and clean deposit the preliminary scratch-brushing has to be executed with special care ; but even then the color of the brass deposit will some- times be found to possess a disagreeable gray tone. This is very likely largely due to the quality of the iron itself, and it is advisable first to give the casting a thin coat of nickel or tin, upon which a deposit of brass of the usual brilliancy can be rr 1 '-" DEPOSITION OF COPPER, BRASS, AND BRONZE. 247 produced. In baths serving for brassing iron articles, a large excess of potassium cyanide must be avoided ; it is, however, an advantage to increase the content of carbonate of soda. Brassing by contact and dipping. Some authors have given directions for brassing by contact for instance, Bacco, Weil, and others but the results obtained are so unsatisfactory, and the process so uncertain, that it is not necessary to enter into further details. The inlaying with black of brassed articles is done in the same manner as described under " Coppering." For oxidizing, platinizing, and coloring of brass, see the proper chapter. 3. Bronzing. Tbe electro-plating of metallic objects with bronze, i. e., a copper-tin alloy, or an alloy of copper, tin, and zinc, is but seldom practised, the bronze tone being in most cases imitated by a deposit of brass, with a somewhat larger content of copper. For coating wrought- and cast-iron with bronze, Gountier re- commends the following solution: Yellow prussiate of potash 10^ ozs., cuprous chloride 5^ ozs., stannous chloride (tin salt) 14 ozs., sodium hyposulphite 14 ozs., water TO quarts. According to Ruolz, a bronze bath is prepared as follows: Dissolve at 122 to 140 F., cyanide of copper 2.11 ozs., and oxide of tin 0.7 oz. in 10 quarts of potassium cyanide solution of 4 Be. The solution is to be filtered. Eisner prepares a bronze bath by dissolving 21 ozs. of blue vitriol in 10 quarts of water, and adding a solution of 2^ ozs. of chloride of tin in potash lye. Salzede recommends the following bath, which is to be used at between 86 and 95 F. : Potassium cyanide 3J^ ozs., car- bonate of potash 35 J^ ozs., stannous chloride (tin salt) 0.42 oz., cuprous chloride ^ oz., water 10 quarts. Weil and Newton claim to obtain beautiful bronze deposits from solutions of the double tartrate of copper and potash, and 248 KLECTRO-DEPOSITION OF METALS. the double tartrate of the protoxide of tin and potash, with caustic potash, but fail to state the proportions. The above formulae are here given with all reserve, since ex- periments with them failed to give satisfactory results ; with Gountier's, Ruolz's, and Eisner's baths no deposit was obtained, but only a strong evolution of hydrogen, while even with a strong current Salzede's bath did not yield a bronze deposit, but simply one of tin. The following method of preparing a bronze bath may be recommended : Prepare, each by itself, solutions of phosphate of copper and stannous chloride (tin salt) in sodium pyrophos- phate. From a blue vitriol solution precipitate, with sodium phosphate, phosphate of copper, allow the latter to settle, and after pouring off the clear supernatant fluid bring it to solution by concentrated solution of sodium pyrophosphate. On the other hand, add to a saturated solution of sodium pyrophos- phate solution of tin salt as long as the milky precipitate formed dissolves. Of these two metallic solutions add to a solution of sodium pyrophosphate, which contains about I ^ ozs. of the salt to the quart, until the precipitate appears quickly and of the desired color. For anodes, use cast bronze plates, which dissolve well in the bath. Some sodium phosphate has from time to time to be added to the bath, and if the color becomes too light, solution of copper, and if too dark, solution of tin. For deposits of tombac Hess's bath (formula VIL, brassing) with anodes of plate or sheet tombac can be recommended ; 3 to 3.5 volts being the most suitable tension of the current for the decomposition of the bath. For nickel bronze, see p. 220. The execution of bronzing requires the same attention and manipulations as given for brassing. DEPOSITION OF SILVER. 249 CHAPTER IX. DEPOSITION OF SILVER. Properties of silver. Pure silver is the whitest of all known metals; it takes a fine polish, is softer and less tenacious than copper, but harder and more tenacious than gold. It is very malleable and ductile, and can be obtained in exceedingly thin leaves and fine wire. Its specific gravity is 10.48 to 10.5, ac- cording to whether it is cast or hammered. It melts at about 1832 F. It is unacted upon by the air, but in the atmosphere of towns it gradually becomes coated with a film of silver sul- phide. It is rapidly dissolved by nitric acid, nitrogen dioxide being evolved ; hydrochloric acid has but little action upon it even at boiling heat ; when heated with concentrated sulphuric acid it yields sulphur dioxide and silver sulphate. Silver baths. Only formulae for approved baths will be given. Silver bath for a heavy electro-deposit of silver (silvering by weight). I. 98 per cent, potassium cyanide 14 ozs., fine silver as silver chloride 8^ ozs., distilled water 10 quarts. \a. 98 per cent, potassium cyanide 8^ ozs., fine silver as silver cyanide 8^ ozs., distilled water 10 quarts. Before describing the preparation of the bath a few words may be said in regard to the old dispute whether it is preferable to use silver cyanide or silver chloride. Without touching upon all the arguments advanced, it may be asserted by reason of conscientious comparative experiments that the results are the same and that the life of the bath is also the same whether one or the other salt has been used in the original preparation. From a theoretical standpoint, silver cyanide must be given the preference ; but as the disadvantages in respect to the life of the bath ascribed by some to silver chloride do not exist, it might be advisable for tho?e who prepare their own baths to use silver chloride. Preparation of bath I. with silver chloride. Dissolve 14 ozs. 250 ELECTRO-DEPOSITION OF METALS. of chemically pure nitrate of silver, best the crystallized and not the fused article, in 5 quarts of water, and add to the solution pure hydrochloric acid or common salt solution, with vigorous stirring or shaking, until a sample of the fluid filtered through a paper filter forms no longer a white caseous precipitate of silver chloride when compounded with a drop of hydrochloric acid. These, as well as the succeeding operations until the silver chloride is complete, have to be performed in a darkened room, as silver chloride is partially decomposed by light. Now separate the precipitate of silver chloride from the solution by filtering, using best a large bag of close felt, and wash the pre- cipitate in the felt bag with fresh water. Continue the washing until blue litmus-paper is no longer reddened by the wash- water, if the hydrochloric acid was used for precipitating, or, if common salt solution was used, until a small quantity of the wash-water on being mixed with a drop of lunar caustic solu- tion produces oaly a slight milky turbidity and no precipitate. Now bring the washed silver chloride in portions from the felt bag into a porcelain mortar, rub it with water to a thin paste, and pour the latter into the potassium cyanide solution consist- ing of I4ozs. of 98 per cent, potassium cyanide in 5 quarts of water, in which, with vigorous stirring, the silver chloride gradu- ally dissolves. All the precipitated silver chloride having been brought into solution, dilute with water to 10 quarts of fluid and boil the bath, if possible, for one hour, replacing the water lost by evaporation. A small quantity of black sediment contain- ing silver thereby separates, from which the colorless fluid is filtered off. The sediment is added to the silver residues and is worked together with them for the recovery of the silver by one of the methods to be described later on. Preparation of bath la. with silver cyanide. Dissolve 14 ounces of chemically pure crystallized nitrate of silver in 5 quarts of water, and precipitate the silver with prussic acid, adding the latter until no more precipitate is produced by the addition of a few drops of prussic acid to a filtered sample of the fluid. Now filter, wash out, and proceed for the rest exactly DEPOSITION OF SILVER. 251 as stated for the bath with silver chloride, except that only ounces of potassium cyanide are taken for dissolving the silver cyanide. In working with prussic acid avoid inhaling the vapor which escapes from the liquid prussic acid, especially in the warm season of the year ; and be careful the acid does not come in contact with cuts on the hands. It is one of the most rapidly acting poisons. Cyanide of silver may also be prepared as follows : Dissolve 14 ounces of chemically pure crystallized nitrate of silver in 5 quarts of water, and add moderately concentrated potassium cyanide solution until no more precipitate is formed, avoiding, however, an excess of the precipitating agent, as it would again dissolve a portion of the cyanide of silver. The precipitated cyanide of silver is filtered off, washed and dissolved in potas- sium cyanide, as above described. The bath prepared according to formula I. or la., serves chiefly for thickly silvering objects of German silver ; it may, however, be used for silvering other metals by weight. Silver bath for ordinary electro- silvering. II, 98 per cent. potassium cyanide 6)^ to 7 ounces, fine silver (as silver nitrate or chloride), 3^ ounces; distilled water, 10 quarts. To prepare the bath dissolve 5J^ ounces of chemically pure crystallized nitrate of silver in 5 quarts of distilled water; in the other 5 quarts of water dissolve the potassium cyanide, and mix both solutions. Or, if chloride of silver is to be used, precipi- tate the solution of 3 J^ ounces of the silver salt in the same manner as given for formula I. ; wash the precipitated chloride of silver, and dissolve it in the potassium cyanide solution. Vats of stoneware, enameled iron, or lined with ebonite mass are to be used for the silver baths. Treatment of the silver baths ; the silver anodes. Frequently the error is committed of adding too much potassium cyanide to the bath. A certain excess of it must be present, and, in the formulae given, this has been taken into consideration. For dissolving the cyanide of silver prepared from 14 ounces of nitrate of silver, as given in formula la, only about 5J^ ounces 252 ELECTRO-DEPOSITION OF METALS. of potassium cyanide are required, and the consequence of work- ing with such a bath devoid of all excess would be that, on the one hand, the bath would offer considerable resistance to the current, and, on the other, that the deposit would not be uni- form and homogeneous. Hence with the use of a medium strong current about 30 to 35 per cent, more potassium cyanide than fine silver fs taken. In working with a stronger current, this excess would, however, be too large, in consequence of which the deposit would not adhere properly and would peel off in scratch-brushing. And again, with a weak current the baths can, without disadvantage, stand a larger excess. As a rule, however, the proportion between fine silver and potassium cyanide in the above formula may be considered as normal, and the current-strength will have to be regulated so that a deposit of fine structure, which adheres firmly, is formed. The most suitable current-strength per 1^/4 square inches of surface is 0.25 to 0.15 ampere, and 0.5 to 0.75 volt tension; the tension of a Daniell element being more than sufficient for the decom- position of the silver bath. On account of the silver bath re- quiring a current of slight electro-motive force, the Smee ele- ment, which yields 0.48 volt, is much liked for silvering in this country and in England. The Bunsen element may, however, also be used if the surface to be silvered is made to correspond with the energy of such an element ; or if a resistance board is placed in the circuit, which is advisable in all cases. On ac- count of the slight electro-motive force required in silvering larger surfaces of objects, the elements are not to be coupled one after the other for electro-motive force, but alongside one another for quantity. In no case must an evolution of hydro- gen be perceptible on the articles, and the current must be more weakened the larger the excess of potossium cyanide in the bath. Whether too much, or not enough, potassium cyanide is present in the bath is indicated by the appearance of the silvered objects and the properties of the deposit, as well as by the be- havior of the anodes in the bath during and after silvering. DEPOSITION OF SILVER. 253 It may be accepted, as a rule, that with a moderate current the object must, in the course of 10 to 15 minutes, be coated with a thin, dull white film of silver. If this be not the case and the film of silver shows a meagre bluish-white tone, potassium cyanide is wanting. However, if, on the other hand, the dull white deposit forms within 2 to 3 minutes, and shows a crystal- line structure, or a dark tone playing into gray- black, the con- tent of potassium cyanide in the bath is too large, provided the current is not excessively strong. If copper and brass become coated with silver without the assistance of the current, the bath contains also too much potassium cyanide. In silvering, even if the objects are to be but thinly coated, insoluble platinum anodes should never be used, but only anodes of fine silver, which are capable of keeping the content of silver in the bath quite constant. From the behavior and appearance of the anodes, a conclusion may also be drawn as to whether the content of potassium cyanide in the bath is too large or too small. If the anodes remain silver-white during silvering, it is a sure sign that the bath contains more potas- sium cyanide than is necessary and desirable ; but if they turn gray or blackish, and retain this color after silvering when no current is introduced into the bath for a quarter of an hour or more, potassium cyanide is wanting. On the other hand, the correct content of potassium cyanide is present when the anodes acquire during the silvering process a gray tone, which, after the interruption of the current, gradually changes back to a pure white. The proposition to use steel plates in place of silver anodes cannot be approved, and as regards such anodes the reader is referred to what is said under " Gilding." If it is shown by the process of silvering itself or by the ap- pearance of the articles or of the anodes that potassium cyanide is wanting in the bath, it should be quickly added, though never more than 30 to 37^ grains per quart of bath at one time, so as to avoid going to the other extreme. Too large a content of potassium cyanide is remedied by adding to the bath, with 254 ELECTRO-DEPOSITION OF METALS. constant stirring, a small quantity of cyanide or chloride of silver rubbed with water to a thinly-fluid paste, whereby the excess is rendered harmless in consequence of the formation of the double salt of silver and potassium cyanide. Instead of such addition, the current may, however, be used as a corrector of the excess. For this purpose suspend as many silver anodes as possible to the anode-rods, but only a single anode as an object to the object rod, and allow the current to pass for a few hours through the bath, whereby the excess of potassium is cyanide rendered innoxious by the dissolving silver. The bath can be kept quite constant by silver anodes, pro- vided potassium cyanide be regularly added at certain intervals, and the anode-surface is equal to that of the objects to be sil- vered. But since, on account of the expense, a relatively small anode surface is frequently used, the content of silver in a bath continuously worked will finally become lower, and augmenta- tion, by the addition of silver, will be required. The manner of effecting this augmentation depends on whether the baths are used for silvering by weight or for lighter silvering, or whether the baths are worked without stopping from morning till evening. If the content of silver in baths I. and la. is not to be augmented by the current itself, it is best to use ex- clusively solution of silver cyanide in potassium cyanide. If, however, the working of such a bath can for some time be in- terrupted, then add not too small a quantity of potassium cyanide to the bath, and, after hanging a small silver anode on the object-rod and a sufficient number of anodes on the anode- rods, dissolve with not too weak a current silver from the anodes until the latter, which at first remain white, begin to acquire a gray tone. Silver is, of course, deposited upon the anode sus- pended as an object, which is, however, not lost, it being dis- solved later on when the anode is secured to the anode-rod. The quantity .of silver dissolved is considerably larger than that deposited upon the small anode-surface suspended as an object. It has previously been mentioned that with proper treatment baths made with chloride of silver have the same duration of life DEPOSITION OF SILVER. 255 as those prepared with cyanide of silver. The chief feature of such proper treatment is the augmentation of the content of silver by electrolysis, i. e., by the current itself. If it were not possible to proceed in this manner, the bath, by the frequently repeated additions of solution of the chloride, instead of the cyanide of silver, in potassium cyanide, would gradually thicken by reason of the potassium chloride which is thereby simul- taneously introduced, and in consequence of this would offer greater resistance to the current. The fear expressed by some that a crystalline separation of potassium chloride, and the consequent formation of a porous deposit upon the objects, might take place, is erroneous, potassium chloride being one of the most soluble salts and showing but little tendency to sepa- rate in crystals from aqueous solutions. The above-mentioned gradual thickening is, however, a disadvantage, which shows itself by the deposit being less homogeneous, and for this reason it is advisable, when silvering by weight, to use silver cyanide instead of the chloride for strengthening the silver bath. A gradual thickening of the bath may also take place if potas- sium cyanide containing potash is used instead of the prepara- tion free from potash, and of 98 to 99 per cent, purity. Even pure fused potassium cyanide produces a thickening of the bath, which, however, progresses very slowly. This thickening is due to a portion of the excess of potassium cyanide being converted by the action of the air into potassium carbonate. The latter thus formed must from time to time be neutralized, which is mostly done with prussic acid, the potassium carbon- ate being thereby converted into potassium cyanide. Instead of prussic acid, calcium cyanide or barium cyanide may be added as long as a precipitate of calcium carbonate or barium carbonate is formed, the clear solution being separated from the precipitate by filtering. For augmenting the content of silver in baths prepared ac- cording to formula II., solution of nitrate of silver or of chloride of silver in potassium cyanide may unhesitatingly be used, since the thickening proceeds more slowly on account of the smaller I 256 ELECTRO-DEPOSITION OF METALS. content of salt in the bath, and because a cheaper bath can be more readily renewed without the sacrifice of money than one for heavy silvering. The recovery of silver from old baths is ef- fected by one of the methods given later on. To determine whether the bath contains silver and excess of potassium cyanide in proper proportions, the following method may be used: Dissolve I gramme (15.43 grains) of chemically pure crystallized nitrate of silver in 20 grammes (0.7 oz.) of water, and gradually add this solution, with constant stirring with a glass rod, to 100 grammes (3.52 ozs.) of the silver bath in a beaker glass as long as the precipitate of silver cyanide formed dissolves by itself. If, after adding the entire quantity of silver solution, the precipitate dissolves rapidly, too large an excess of potassium cyanide is present in the bath ; and vice versa, if the precipitate' does not completely dissolve after stirring, potassium cyanide is wanting. While this experiment allows us to judge of the proportion of silver to potassium cyanide, it does not throw any light upon the effective content of silver in the bath, and for refreshing the latter, it is desirable to know the actual content of silver in it To determine this, mix 25 cubic centimetres of the silver bath in a beaker glass with 50 cubic centimetres of pure hydro- chloric acid and 50 cubic centimetres of water, and heat upon a water or sand bath until all odor of prussic acid has disap- peared, and then dilute with 200 cubic centimetres of water. Filter off the precipitate of chloride of silver formed through a weighed filter, previously dried at 212 F., wash the precipitate with hot distilled water until the filtrate is no longer rendered turbid by a drop of silver solution ( I part of nitrate of silver to 20 of water), and dry at 212 F. until the weight remains con- stant. After deducting the weight of the dried filter, the weight of the precipitated chloride of silver is obtained, and from this the weight of the metallic silver is calculated according to the following formula: 143.5 : IQ 8 = grammes of chloride of silver found : x. DEPOSITION OF SILVER. 257 The content of silver in the bath per liter is then found by multiplying x by 40. In silvering, the constant agitation of the layers of fluid is of decided advantage, streaks being otherwise readily formed upon the silvered objects. To keep the articles in gentle motion while in the bath, one method is to connect the suspending rods to a frame of iron having four wheels, about 3 inches in diameter, connected to it, which slowly travel to and fro to the extent of 3 or 4 inches upon inclined rails attached to the upper edges of the tank, the motion, which is both horizontal and vertical, be- ing given by means of an eccentric wheel driven by steam FIG. 115. power. By another arrangement, the frame supporting the articles does not rest upon the tank, but is suspended above the bath, and receives a slow swinging motion from a small eccentric or its equivalent. In the Elkington establishment at Birmingham the following arrangement is in use : All the sus- pending rods of the bath rest upon a copper mounting, which, by each revolution of an eccentric wheel, is lifted about ^ inch, and then returned to its position ; the copper mounting is connected to the main negative wire of the dynamo-machine by a copper cable. The same object may also be attained by 258 ELECTRO-DEPOSITION OF METALS. giving the objects a t horizontal instead of vertical motion, as shown in Fig. 115, in which the motion is produced by an ec- centric wheel on the side. Finally it remains to mention a singular phenomenon in silvering which has not yet been explained. A small addition of certain, and especially of organic, substances, which, how- ever, must not be made suddenly or in too large quantities, pro- duces a fuller and better adhering deposit of greater lustre than can be produced in fresh baths. Elkington observed that an addition of a few drops of carbon disulphide to. the bath made the silvering more lustrous, while others claim to have used with success solutions of iodine in chloroform, of gutta-percha in chloroform, as well as heavy hydrocarbons, tar, oils, etc. However, many baths have been entirely spoiled by an attempt to change them into bright working baths by the addition of such ingredients ; and hence it is best to leave such experi- ments alone. There is no doubt that a silver bath becomes better in the degree as it takes up small quantities of organic substances from dust and air. Fresh silver baths will more rapidly accommodate themselves to regular working by the x addition of a few drops of spirit of sal ammoniac. After silvering the objects frequently show, instead of a pure white, a yellow tone, or they become yellow in the air, which is ascribed to the formation of basic silver salts in the deposit. To overcome this evil it has been proposed to allow the objects to remain in the bath for a few minutes after interrupting the cur- rent, whereby the basic salts are dissolved by the potassium cyanide of the bath ; or the same object is attained by invert- ing the electrodes for a few seconds, after plating, thus trans- forming the articles into anodes. The electric current carries away the basic salt of silver in preference to the metal. This operation should, of course, not be prolonged, otherwise the silver will be entirely removed from the objects, and will be de- posited on the anodes. For the same purpose some electro- platers hold in readiness a warrn solution of potassium cyanide, in which they immerse the silvered articles for half a minute. DEPOSITION OF SILVER. 259 It has been proposed to add to the silver baths a solution of nickelous cyanide in potassium cyanide in order to obtain a deposit of a silver-nickel alloy which is claimed to be dis- tinguished by its greater hardness and the property of not turn- ing so readily dark. Numerous experiments with solutions of cyanide of silver and nickelous cyanide in potassium cyanide in all possible proportions, and under various tensions of current and subsequent analysis of the deposits obtained, showed, how- ever, only inconsiderable traces of nickel in the silver deposit, which had but a very slight influence upon the hardness and durability of the silver. The London Metallurgical Co. endeavors to attain greater hardness and power of resistance of the silver by adding zinc cyanide or cadmium cyanide, and has given to this process the name of areas silvering. According to the patent an addition of 20 to 30 per cent, of zinc or cadmium to the silver prevents the tarnishing of the plating, and besides the deposit is claimed to be lustrous and hard. For areas silvering the appropriate quantity of zinc or cadmium or a mixture of both metals is con- verted into potassium-zinc cyanide or potassium-cadmium cyan- ide, and this solution is mixed with a corresponding quantity of solution of potassium silver cyanide, with a small excess of potassium cyanide. Sheets of a silver-zinc or a silver-cadmium _^alloy are used as anodes. Some English electro-platers claim that for many articles, especially bicycles, areas silvering may be substituted for nickel- ing. The following experiments may serve as an illustration re- garding the value of this process as a substitute for silver-plating instruments and articles of luxury: A bath was prepared which contained per quart 231^ troy grains of fine silver and 77 troy grains cadmium in the form of cyanide double salts with a small excess of potassium cyanide. The most suitable tension of current for the decomposition of a pure potassium-cadmium cyanide solution which contained per quart 154 troy grains of cadmium with the same excess of 260 ELECTRO-DEPOSITION OF METALS. potassium cyanide as the above-mentioned mixture, was found to be 2 volts. In electrolyzing the cadmium-silver bath at 0.75 volt, a uni- form silver-white deposit similar to that of pure silver was at first formed. However, after two hours the deeper places of the objects suspended in the bath showed crystalline ex- crescences which felt sandy and could be rubbed off with the fingers. After scratch-brushing the articles and again suspend- ing them in the bath, these sandy non-adhering metallic deposits were rapidly reformed. An analysis of the deposit separated from the articles showed 96.4 per cent, silver and 3.2 per cent, cadmium. This deposit could without difficulty be polished with the steel like a pure silver deposit, and hence its hardness would not seem greater than that of pure silver. Its capability of resisting hydrogen sulphide as compared with that of pure silver was scarcely greater. In another experiment electrolysis was effected with 1.25 volts. The deposit showed from the start a coarser structure, and the formation of the sandy non-adhering deposit took place much more rapidly. But, on the other hand, the hardness of the separated coherent metal was greater than that of pure silver, and also its power of resisting hydrogen sulphide. An analysis of the deposit showed 92.1 per cent, silver and 7.8 per cent, cadmium. In both cases the deposit was dull like that of pure silver. With a greater tension of current the quantity of cadmium in the deposit increased and the hardness of the latter became correspondingly greater. However, these deposits could not be considered serviceable for the above-mentioned purpose, because they could not be made of sufficient thickness as required for solid silver-plating of forks and spoons. Execution of silvering. A. Silvering by weight. Copper, brass, and all other copper alloys may be directly silvered after amalgamating (quicking), whilst iron, steel, nickel, zinc, tin, lead, and Britannia are first coppered or brassed, and then amalgamated. DEPOSITION OF SILVER. 26 1 The mechanical and chemical preparation of the objects for the silvering process is the same as described on pages 150 and 156. To obtain well-adhering deposits great care must be ex- ercised in freeing the objects from grease and in pickling. As a rule, objects to be silvered are ground and polished ; but polishing must not be carried too far, since the deposit of silver does not adhere well to highly polished surfaces; and in case such highly-polished objects are to be silvered it is best to deprive them of their smoothness by rubbing with pumice powder, emery, etc., or by pickling. The treatment of copper and its alloys, German silver and brass, which have chiefly to be considered in silvering by weight, is, therefore, as follows: 1 . Freeing from grease by hot potash or soda lye ( I part of caustic alkali to 8 or 10 parts of water), or by brushing with the lime-paste mentioned on page 157. 2. Pickling in a mixture of I part, by weight, of sulphuric acid of 66 Be. and 10 of water. This pickling is only required for rough surfaces of castings, ground articles being imme- diately after freeing from grease treated according to 3. 3. Rubbing with a piece of cloth dipped in fine pumice powder or emery, after which the powder is to be removed by washing. 4. Pickling in the preliminary pickle, rinsing in hot water, and quickly drawing through the bright dipping bath (page 152), and again thoroughly rinsing in several waters. 5. Amalgamating (quicking} by immersion in a solution of mercury, called the quicking solution, and consisting of a solu- tion of 0.35 ounce of nitrate of mercury in I quart of water, to which, with constant stirring, pure nitric acid in small portions is added until a clear fluid results ; a weak solution of potas- sium-mercury cyanide in water is, however, preferable for quicking. 6. In the quicking solution the objects remain only long enough to acquire a uniform white coating, when they are rinsed in clean water, and gone over with a brush in case the quicking shows a gray instead of a white tone. 262 ELECTRO-DEPOSITION OF METALS. The objects are now brought into the silver bath and secured to the suspension rods by slinging-wires of copper. For forks and spoons these wires are bent on their extremities FIG. 116. j n suc ] 1 a manner that the fork or spoon may readily be^inserted or removed. Fig. 116 presents this ter- minal hook. The straight portion of these wires which dips into the liquid is covered with a small tube of India rubber or coated with ebonite mass, which prevents the useless deposit of silver upon it. The hooped portions, however, become coated with silver, which may be removed by the use of acids after having raised the India-rubber tube. Introduce into the bath at first a somewhat more powerful current, so that the first deposit of silver takes place quite rapidly, and after 3 minutes regulate the current so that in 10 to 15 minutes the objects are coated with a thin, dull film of silver. At this stage take them from the bath, and after seeing that all portions are uniformly coated with silver, scratch-brush them with a brass brush, which should, however, not be too fine. In doing this the deposit must not raise up ; if at this stage the objects stand thorough scratch-brushing, raising of the deposit in burnishing later on need not be feared. Any places which show no deposit of silver are vigorously scratch-brushed with the use of pulverized tartar, then again carefully cleansed by brushing with lime-paste to remove any impurities due to touching with the hands, pickled by dipping in potassium-cyanide solution, rinsed off again, quicked, and after careful rinsing returned to the bath. Special care must be had not to contaminate the bath with quicking solution, as this would soon spoil it. The objects now remain in the bath until the deposit has ac- quired a weight corresponding to the desired thickness. Knives, forks, and spoons receive a deposit of 2.1 1 to 3.52 ozs. of silver per dozen, such deposit being produced with elements in 10 to 14 hours, and with a dynamo-electrical machine in 4 to 5 hours. According to Dr. William H. Wahl, the amount of silver de- * DEPOSITION OF SILVER. 263 posited upon the several grades of plated table-ware manu- factured by the William Rogers Manufacturing Co., of Hartford, Conn., is as follows: Per gross. Extra plate. Double plate. Triple plate. Teaspoons 48 dwts. 4 ozs. 6 ozs. Desertspoons and forks . . . . 72 " 6 " 9 " Tablespoons and med. forks. 96 " 8 " 12 " In order to control the weight of the deposit proceed as follows : After having removed one of the pans of a sensitive beam balance, substitute for it a brass rod which keeps the other pan in equilibrium. Under this rod place a vessel filled with pure water and of sufficient diameter and depth to allow of the article suspended to the rod dipping entirely into the water without touching the sides of the vessel. Suppose now that several dozen spoons of the same size and shape are at the same time to be provided with a deposit of a determined weight, it suffices to control the weight of the deposit of a single spoon, and when this has acquired the necessary deposit all the other spoons will also be coated with a deposit of silver of the same thickness as the test spoon. After quicking and carefully rinsing the spoons, one of them is suspended to the brass rod of the balance so that it dips entirely under water ; the equilibrium is then re-established by placing lead shot upon the pan of the scale, and edding the weight corresponding to the deposit the spoon is to receive. Now bring the weighed spoon together with the rest into the bath, and proceed with the silvering pro- cess in the ordinary manner. After some time the weighed spoon is taken from the bath, rinsed in water, and hung to the brass rod of the scale; if it does not restore the equilibrium of the latter, it is returned to the bath, after some time again weighed, and so on until its weight corresponds to that of the lead shot and weight placed in the pan of the scale, when it is assumed that the balance of the articles have also received their proper quantity and that the operation is complete. A more complete weighing apparatus is the plating balance 264 ELECTRO-DEPOSITION OF METALS. first used by Brandely and later on improved by Roseleur. The apparatus, which is shown in Fig. 117, is designed for obtaining deposits of silver " without supervision and with con- FIG. 117. stant accuracy, and which spontaneously breaks the current when the operation is terminated." It is manufactured in various sizes, suitable for small or large operations. It consists of: I. A wooden vat, the upper edge of which carries a brass winding-rod having a binding screw at one end to receive the positive conducting wire of the battery ; from this rod the anodes are suspended, which are entirely immersed in the solution, and communicate with brass cross-rods by means of platinum wire hooks. These cross-rods are flattened at their DEPOSITION OF SILVER. 265 FIG. 1 1 8. ends so that they may not roll, and at the same time have a better contact with the " winding-rod." 2. A cast-iron column screwed at its base to the side of the vat, and which carries near the top two projecting arms of cast-iron, the extremities of which are vertical and forked, and may be opened or closed by iron clamps. These forks are intended for sustaining the beam and preventing the knives from leaving their bearings under the influence of too violent oscillations. In the middle of the two arms are two wedge-shaped recesses of polished steel to receive the knife edge? of the beam. One of the arms of the column carries at its end a horizontal ring of iron in which is fixed a heavy glass tube sup- porting a cup of polished iron which is insulated from the column (Fig. 118). This cup has at its lower part a small pocket of lamb-skin or of India rubber, which by means of a screw beneath may be raised or lowered. This flexible bottom allows the operator to lower or raise at will the level of the mercury introduced afterwards into the iron cup. Another lateral screw permits connection to be made with the negative electrode. 3. A cast-iron beam carrying in the middle two sharp knife-edges of the best steel hardened and polished. At each extremity there are two parallel bearings of steel separated by a notch, and intended for the knife edges of the scale-pan that receives the weights, and those of the frame supporting the articles to be silvered. One of the arms of the beam is provided with a stout platinum wire, placed im- mediately above and in the centre of the cup of mercury. According as the beam inclines one way or the other, this wire plays in or out of the cup. 4. A scale-pan for weights, with two knife edges of cast-steel, which is attached to four chains supporting a wooden pan for the reception of weights. A smaller pan above is intended for the weights corresponding to that of the silver to be deposited. 5. The frame for support- 266 ELECTRO-DEPOSITION OF METALS. ing the articles to be silvered, which is also suspended from two steel knife edges, and the rod of which is formed of a stout brass tube attached below to the brass frame proper, which last is equal in dimensions to the opening of the vat, and supports the rods to which the articles are suspended. Fig. 119 shows a Roseleur plating balance, together with the resistance board, voltmeter, and silver bath ; and will be under- stood without further explanation. FIG. 119. For calculating the weight of the deposit from the density of current, see " Chemical and Electric Equivalents." When the articles have received a deposit of the required weight, they are treated for the prevention of subsequent yellow- ing according to one of the methods given on p. 258, then DEPOSITION OF SILVER. 267 scratch-brushed with the use of decoction of soap-root, plunged in hot water, and dried in sawdust. Articles which are to retain the beautiful crystalline dead white with which they come from the bath are, without touch- ing them with the fingers or knocking them against the sides of the vessel, plunged into very hot clean water and then sus- pended free to dry; immediately after drying they are to be provided with a thin coat of kristalline or zapon to protect the dead white coating which readily turns yellow, and, moreover, is very sensitive. The silvered articles having been scratch-brushed, must finally be polished, which may be effected upon a fine felt wheel with the use of rouge, but imparting high lustre by burnishing is to be preferred, the deposit being first treated with the steel burn- isher and then with the stone burnisher, as explained on p. 149. The steel burnisher consists of a piece of polished steel varying in shape mounted in a wooden handle. The operation of burn- ishing is very simple. Take hold of the tool very near to the steel or stone, and lean very hard with it on those parts which are to be burnished, causing it to glide by a backward and for- ward movement without taking it from the piece. When it is requisite that the hand should pass over a large surface at once, without losing its point of support on the work-bench, in taking hold of the burnisher be careful to place it just underneath the little finger. By these means the work is done more quickly, and the tool is more solidly fixed in the hand. During the whole process the tool must be continually moistened with soap-suds. In some establishments in which plated table-ware in large quantity is turned out, ingeniously devised burnishing machines driven by power are in use, by which much of the manual labor is spared. The knife, spoon, etc., each supported by its tips in a suitable holder, are very slowly rotated, while the burnishing tool moves quickly over the surface, performing the work rapidly and satisfactorily. When the burnishing is completed, the surface is wiped off 268 ELECTRO-DEPOSITION OF METALS. longitudinally with an old, soft calico rag ; sawdust, hard cloth, and tissue paper produce streaks. B. Ordinary silvering. The operations the objects which are to receive a deposit of less thickness have to undergo, are ex- actly the same as those described under silvering by weight, the only difference being that for quicking a weaker solution (15 to 3 1 grains of nitrate of mercury to I quart of water) or very dilute solution of potassium- mercury cyanide is used, and that the objects remain in the bath for a shorter time. As previ- ously mentioned, iron, steel, zinc, tin, etc., should first be coppered or brassed ; however, tin in its alloys may also be directly silvered in the silver bath, but a larger excess of potas- sium cyanide is required than for copper, brass, or German silver. According to Dr. William H. Wahl, in the United States, the practice of previous coppering is not adopted either with Bri- tannia metal or steel. The practice of different establishments of cleansing their work differs somewhat, but all aim at the same result, viz., to secure a smooth adhering coating of metal upon an inferior base. The practice of the Meriden Britannia Co.'s works at Meriden, Conn., as observed by Dr. William H. Wahl, is substantially as follows: With Britannia or " white metal :" The article is first cleansed of all grease by immersion in boiling alkali ; then into dilute muriatic acid; then into a ''striking" solution, viz., a weak cyanide of silver solution with a large proportion of free cyanide of potassium, and a large silver anode operated with a very strong electric current. The purpose of immersion in this solution is to effect an instantaneous deposit of silver on the metal, to better insure a perfect coating in the silver bath proper. The articles remain in the " striking " solution for a few seconds only, as its action, owing to the large proportion of free cyanide it contains, is very prompt, and as soon as they have received a thin coating, which takes place almost imme- diately, they are removed to the electro-plating bath, where they remain until they have received the proper coating of DEPOSITION OF SILVER. 269 silver. In many cases, especially with articles of considerable size, cleansing in boiling alkali must be supplemented by scratch- brushing, in which case the acid dip may be dispensed with, and the article, after thorough rinsing and dipping in alkali to re- move finger-marks, is immersed at once in the " striking " solu- tion. German silver or nickel articles are first cleansed in boiling alkali, washed, then dipped in a mixture of two-thirds sulphuric acid and one-third nitric acid, then into quicking solution, then into the " striking" solution, and from this into the plating bath. Steel articles are cleansed in boiling alkali, rinsed, dipped in muriatic acid, then in the "striking" solution, and from this into the plating bath. In case the articles require scouring the acid dip is dispensed with. For steel two " striking " solutions are used, one somewhat richer in silver than the other, the weaker solution being used first. With the William Rogers Manufacturing Co., Hartford, Conn., the following is the general outline of the methods in use for preparing work for plating: For cleansing (steel) cutlery. Immersion in boiling alkali for the removal of grease ; scouring; rinsing; dipping into strong muriatic acid ; then for a few seconds in a silver " striking " solution ; then in a plating bath until the required amount of silver is deposited. The formula for the " striking " solution, which will be given later on, is low in silver, rich in cyanide, and worked with a strong current and silver anode. Nickel-silver ( German silver) for spoons. Immerse in boil- ing alkali; scouring, if necessary rinsing in water; immersion in acid mixture, composed of two-thirds sulphuric acid and one- third nitric acid; dipping in weak quicking solution (either very dilute potassium-mercury cyanide or acidulated nitrate of mercury) ; immersion for a few seconds in the silver " striking" solution ; and from this into the plating bath. Britannia metal {hollow-ware) . Cleansing in alkali as above ; rinsing in water ; again immersing in alkali to remove finger- 2/0 ELECTRO-DEPOSITION OF METALS. marks, if necessary, immersing in the "striking" solution, and from this into the plating solution. A quicking solution for Britannia, sometimes employed, is composed of a strong solu- tion of sal ammoniac and corrosive sublimate, into which the articles are dipped after cleansing in potash. The silver " striking " solution, as used by the Wm. Rogers Manufacturing Co., of Hartford, Conn., is composed as follows : Rogers' s " striking" solution. Cyanide of potassium 6 ozs., silver y% oz., water I gallon. Use a strong current. Meriden Company's " striking solution." Cyanide of potas- sium 12 to 1 6 ozs., silver 8 to 10 dwts., water I gallon. The plating solution commonly employed by the Wm. Rogers Manufacturing Co. has the following composition : Cyanide of potassium 6 ozs., silver (in chlorate) 4 ozs., water I gallon. The usual formula of the Meriden Britannia Co. has the fol- lowing proportions : Cyanide of potassium 12 ozs., silver 3 ozs., water i gallon. In order to secure an extra heavy coating of silver on the convex surfaces of spoons and forks, which, being subject to greater wear than the other parts, require extra protection, the Meriden Britannia Co. uses a frame in which the articles sup- ported therein by their tips are placed horizontally in a shallow silver bath, and immersed just deep enough to allow the pro- jecting convexities to dip into the bath. By this artifice these portions are given a second coating of silver of any desired thickness. This mode of procedure, which is termed "sec- tional" plating, accomplishes the intended purpose nicely and satisfactorily. In some establishments the silvered forks and spoons are placed between plates of gutta-percha of corre- sponding shape, and held together by rubber bands. In these plates the portions to be provided with an extra coating of silver are cut out. By suspending the forks and spoons thus protected in the bath, the unprotected places receive a further layer of silver, the outlines of which are later on smoothed down with burnishers. "Stopping-Off" Stopping-off is the manipulation by which DEPOSITION OF SILVER. 2/1 certain parts of a metallic article, which are already covered with an electro -deposit on its entire surface, are coated with an- other metal. For instance, if it is desired to gild the parts in relief of an article, the other portions are " stopped-off," and vice versa. Stopping-off varnish is prepared by dissolving asphalt or dammar with an addition of mastic in oil of tur- pentine. Apply with a brush, and after thoroughly drying the articles in the drying-chamber, place them for an hour in very cold water, whereby the varnish hardens completely. After plating, the varnish is removed, best with benzine, the article plunged in hot water, and dried in saw-dust. For a varnish that will resist the solvent power of the hot alkaline gilding liquid, Gore recommends the following compo- sition : Translucent rosin 10 parts, yellow beeswax 6, extra-fine red sealing-wax 4, finest polishing rouge 3. Silvering by contact, by immersion, and cold silvering with paste. For silvering by contact with zinc, the bath prepared according to formula II. may be used, adding about 17 grains more of potassium cyanide per quart. The articles are to be prepared in the same manner as for silvering by weight, and quicked in a weak quicking solution. Before placing the arti- cles in the bath they are wrapped round with bright zinc wire, or are brought in contact while in the bath with a bright strip of zinc, care being had to frequently change the points of con- tact to prevent the formation of stains. As previously men- tioned, by the contact of the metal to be silvered with the electro-positive zinc, a weak current is produced which effects the deposition of the silver, but this taking place very slowly, it is best to heat the silver bath. Silver being at the same time deposited upon the zinc, the latter must be frequently freed from the deposit and brightened by means of a file or emery paper. By contact with zinc, silver may also be deposited in one of the following baths for silvering by immersion; Crystallized nitrate of silver 5.64 drachms, 98 per cent, potassium cyanide 1.23 ozs., water I quart. To prepare the bath dissolve the 72 ELECTRO-DEPOSITION OF METALS. silver salt in I pint of distilled water, then the potassium cyanide in the remaining pint of water, and mix the two solu- tions. 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 is not required. The deposit is lus- trous 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 circumstances be called solid. The bath gradually works less effectively and finally ceases to silver, when it may be attempted to restore its action by the addition of 2^ to 5^ drachms of potassium cyanide per quart. Should this prove ineffectual, the content of silver is nearly exhausted, and the bath is evaporated to dryness, and the residue added to the silver waste. Frequent refreshing of the bath with silver salt cannot be recommended, the silvering always turning out best in a fresh bath. A solution of nitrate of silver in sodium sulphide is, accord- ing to Roseieur, very suitable for silvering by immersion. The solution is prepared by pouring into a moderately concentrated solution of sodium sulphide, with constant stirring, solution of a silver salt until the precipitate of silver sulphide formed be- gins to be dissolved with difficulty. This bath can be used cold or warm, fresh solution of silver being added when it com- mences to lose its effect. If, however, the bath is not capable of dissolving the silver sulphide formed, concentrated solution of sodium sulphide has to be added. For the preparation of the solution of sodium sulphide, Rose- ieur recommends the following method : Into a tall vessel of glass or porcelain (Fig. 120) 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 heat- ing copper turnings with concentrated sulphuric acid, washing DEPOSITION OF SILVER, 2/3 the gas in a Woulff bottle filled an inch or so deep with water, and introducing it into the bottle containing the soda solution, as shown in the illustration. A part of the soda becomes trans- formed into sodium sulphide, which dissolves, and a part is pre- cipitated as carbonate. The latter, however, is transformed into sodium sulphide by the continuous action of sulphurous acid, and carbonic acid gas escapes with effervesence. When all has become dissolved, the passage of sulphurous acid should be continued until the liquid slightly reddens blue litmus-paper, and then allowed to stand aside for 24 hours. At the end of / FIG. 1 20. that time a certain- quantity of crystals will be found upon the mercury, and the liquid above, more or less colored, constitutes the sodium sulphide of the silvering bath. The liquid sodium sulphide 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 litmus-paper ; and if the blue color is strongly reddened, carbonate of soda is cautiously added, little by little, in order to neutralize the excess of sul- phurous acid. On the other hand, if red litmus-paper becomes blue, too much alkali is present, and more sulphurous acid gas 18 274 ELECTRO-DEPOSITION OF METALS. must be passed through the liquid, which is in the best condi- tion for our work when it turns litmus-paper violet or slightly red. The solution should mark from 22 to 26 Be., and should not come in contact with iron, zinc, tin, or lead. As will be seen, this mode of preparing the sodium sulphide solution is somewhat troublesome, and it is, therefore, recom- mended to proceed as follows: Prepare a saturated solution of commercial sodium sulphide; the solution will show an alka- line reaction, the commercial salt frequently containing some sodium carbonate. To this solution add, with stirring, solution of bisulphite of sodium saturated at 122 F., until blue litmus- paper is slightly reddened. Then add to this solution concen- trated solution of nitrate of silver until the flakes of silver sul- phide separated begin to dissolve with difficulty. The immersion bath, prepared according to one or the other method, works well and has the advantage of producing silver- ing of a beautiful lustre, such as is desirable for many cheap articles. By allowing the articles to remain for a longer time in the bath, the lustrous deposit becomes dull. For the pro- duction of a lustrous coating the bath should always be used cold. It must further be protected, as much as possible, from the light, as otherwise gradual decomposition takes place. According to Dr. Ebermayer a silver-immersion bath for lustrous silvering is prepared as follows: Dissolve 1.12 ozs. of nitrate of silver in water, and precipitate the solution with caustic potash. Thoroughly wash the silver oxide which is precipitated, and dissolve it in I quart of water which contains 3.52 ozs. of potassium cyanide in solution, and finally dilute the whole with I quart more of water. For silvering, the bath is heated to the boiling point, and the silver withdrawn may be replaced by the addition of moist silver oxide as long as com- plete dissolution 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 not satisfactory, the coating being dull and adhering badly. DEPOSITION OF SILVER. 2/5 For silvering articles, especially those composed of the various alloys of copper, without the use of a current, the following process is recommended in " Edelmetallindustrie." Dissolve silver in nitric acid with the assistance of the sand or water bath, and convert it into chloride of silver by carefully adding hydro- chloric acid or common salt solution until, after repeated stir- ring and allowing to settle, no more precipitate is formed^ Now let the mixture repose, then pour off the supernatant fluid and wash the white caseous precipitate until litmus- paper is no> longer reddened by the wash-water. Keep the chloride of sil- ver thus obtained in wide-mouthed black bottles. Now prepare in glazed pots two baths as follows: i. A potassium-cyanide bath by dissolving 1 1 /^ drachms of chloride of silver and 2 ozs. of potassium cyanide in about 10 quarts of water, and heating the mixture to the boiling point. 2. A salt bath consisting of 10 quarts of water, 1 1 Ibs. of common salt, 1 1 Ibs. of cream of tartar, and 4^ ozs. of chloride of silver. Boil the mixture, with constant stirring, for one hour, and when cold pour it into another pot, in which it may be kept. The articles to be treated are cleansed by treating them with dilute hydrochloric acid. They are next pickled by dipping them in nitric acid, and finally plunged into a bright- dipping bath, consisting of nitric acid, a small quantity of hydrochloric acid and a trace of lamp-black. They are then thoroughly rinsed off, and thrown into water containing a small quantity of cream of tartar, where they remain until they are silvered. The water must not be warm and the articles should not remain in it too long, other- wise they will tarnish and it will be impossible to obtain a pure silvering.- The articles thus prepared are first brought into the potassium-cyanide bath and gently agitated, when they become immediately coated with a thin film of silver. They are then rinsed and brought into a dilute salt bath, prepared by adding water to a portion of the salt given under 2, where they remain until they have acquired a gray-white or yellowish-white color. They are then rinsed, returned to the potassium-cyanide bath, again rinsed and thrown into clean water, or dried in sawdust. 2/6 ELECTRO-DEPOSITION OF METALS. Each rinsing must be effected in a different vessel, The two baths are very lasting and require only a periodical addition of potassium cyanide (when the articles on being immersed be- come black, which turns slov\ly to white) or of chloride of sil- ver (when the articles show a yellowish-white color). When the dilute salt bath becomes too weak, a fresh quantity of the the salt bath is added by means of a wooden spoon. The potassium-cyanide bath must be shaken every day. During the process of silvering the potassium-cyanide bath is to be kept at between 176 and 194 F., and the salt bath at above 212 F. The potassium-cyanide bath should only be boiled before use, when making a fresh addition of potassium cyanide, or of chloride of silver. The silvering obtained with the use of these vats is pure-white, cheap, and durable. The process of coating with a thin film, or rather coloring with silver, small articles such as hooks and eyes, pins, etc., differs from the above-described immersion method, which effects the silvering in a few seconds, in that the articles require to be boiled for a longer time. The process is as follows : Prepare a paste from 14.11 drachms of nitrate of silver, pre- cipitated as chloride of silver; 44 ounces of cream of tartar, and a like quantity of common salt, by precipitating the solu- tion of the nitrate of silver with hydrochloric acid, washing the chloride of silver and mixing it with the above-mentioned quantities of cream of tartar and common salt, and sufficient water to a paste, which is kept in a dark glass vessel to prevent the chloride of silver from being decomposed by the light. Small articles of copper or brass are first freed from grease, and pickled. Then heat in an enameled kettle 3 to 5 quarts of rain-water to the boiling-point; add 2 or 3 heaping teaspoon- fuls of the above-mentioned paste, and bring the metallic objects contained in a stoneware sieve into the bath and stir them diligently with a rod of glass or wood. Before placing a fresh lot of articles in the bath additional silver paste must be added. If finally the bath acquires a greenish color, caused by dissolved copper, it is no longer suitable for the purpose, and is then evaporated and added to the silver residues. DEPOSITION OF SILVER. 277 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 copper) until it is entirely silvered. The paste may also be rubbed in a mortar with some water to a uniform thinly fluid mass, and applied with a brush to the surface to be silvered. By allowing the paste to dry naturally, or with the aid of a gentle heat, the silvering appears. The application of the paste by means of a brush is chiefly made use of for decorating with silver articles thinly gilded by immersion. For articles not gilded, the above-mentioned rubbing on of the stiff paste is to be preferred. Composition of argentiferous pastes. I. Silver in the form of freshly precipitated chloride of silver* 0.35 oz., common salt 0.35 oz., potash 0.7 oz., whiting 0.52 oz., and water a sufficient quantity to form the ingredients into a stiff paste. II. Silver in the form of freshly precipitated chloride of silver* 0.35 oz., potassium cyanide 1.05 oz., 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 composition, which is not poisonous, does ex- cellent 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 I part, pearl-ash 3, common salt i^, whiting I, and sufficient water to form a paste. Apply the latter to the metal to be silvered and rub with a piece of soft leather. When the metal is silvered, wash in water to which a small quantity of washing soda has been added. Graining. In gilding parts of watches, gold is seldom di- rectly applied upon the copper ; there is generally a preliminary * From 0.56 oz. of nitrate of silver. -278 ELECTRO-DEPOSITION OF METALS. operation called graining, by which a grained and slightly dead appearance is given to the articles. Marks of the file are ob- literated by rubbing upon a whetstone, and lastly upon an oil- stone. Any oil or grease is removed by boiling the parts for a few minutes in a solution of 10 parts of caustic soda or potash in 100 of water, which should wet them entirely if all the oil has been removed. The articles being threaded upon a brass wire, cleanse them rapidly in the acid mixture for a bright lustre, 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 or the cork. Next place the cork and the pieces in a weak mercurial solution, composed of water 2^ gallons, nitrate or binoxide of mercury y T oz., sul- phuric acid i oz., which slightly whitens the copper. The pieces are passed quickly through the solution and then rinsed. This operation 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 Ibs. II. Silver powder I oz., cream of tartar 4 to 5 ozs., common salt 13 ozs. III. Silver powder, common salt, and cream of tartar, equal parts by weight of each. The mixture of the three ingredients must be thorough and effected at a moderate and protracted heat. The graining is the coarser the more common salt there is in the mixture, and it is the finer and more condensed as the propor- tion of cream of tartar is greater, but it is then more difficult to scratch-brush. The silver powder is obtained as follows : Dis- solve in a glass or porcelain vessel 2 /$ oz. of crystallized nitrate of silver in 2^/ 2 gallons of distilled water, and place 5 or 6 ribands of cleansed copper, ^ inch wide, in the solution. DEPOSITION OF SILVER. 2/9 These ribands should be long enough to allow of a portion of them being above the liquid. The whole is kept in a dark place, and from time to time stirred with the copper ribands. This motion is sufficient to loosen the deposited silver, and present fresh surfaces to the action of the liquor. When no more silver deposits on the copper, the operation is complete, and there remains a blue solution of nitrate of copper. The silver powder is washed by decantation or upon a filter until there remains nothing of the copper solution, For the purpose of graining, a thin paste is made of one of the above mixtures and water, and spread by means of a spatula upon the watch parts held upon the cork. The cork itself is placed upon an earthenware dish, to which a rotating move- ment is imparted by the left hand. An oval brush with close bristles, held in the right hand, rubs the watch parts in every direction, but always with a rotary motion. A new quantity of paste is added two or three times and rubbed in the manner in- dicated. The more the brush and cork are turned the rounder becomes the grain, which is a good quality, and the more paste added the larger the grain. When the desired grain is obtained the pieces are washed and scratch-brushed. The brushes em- ployed are of brass wire, as fine as hair and very stiff and springy. It is necessary to anneal them upon an even fire to different degrees ; one soft or half-annealed for the first opera- tion or uncovering the grain ; one harder for bringing up the lustre; and one very soft or fully annealed, used before gilding for removing any marks which may have been made by the preceding tool, and for scratch-brushing after gilding, which, like the graining, must be done by giving a rotary motion to the tool. If it happens that the same watch part is composed of copper and steel, the latter metal requires to be preserved against the action of the cleansing acids and of the graining mixture by a composition called resist. This consists in cover- ing the pinions and other steel parts with a fatty composition which is sufficiently hard to resist the tearing action of the bristle and wire brushes, and insoluble in the alkalies of the gild- 280 ELECTRO-DEPOSITION OF METALS. ing bath. A good composition is : Yellow wax 2 parts by weight, translucent rosin 3^, extra fine red sealing-wax I J^ , polishing rouge I. Melt the rosin and sealing-wax in a porce- lain dish, upon a water-bath, and afterwards add the yellow wax. When the whole is thoroughly fluid, gradually add the rouge and stir with a wooden or glass rod. Withdraw the heat, but continue the stirring until the mixture becomes solid, otherwise all the rouge will fall to the bottom. The flat parts to receive this resist 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 alco- hol lamp, and a small quantity of resist is taken with it. The composition soon melts, and by turning the tool around the steel pinion thus becomes coated. Use a scratch-brush with long wires, as their flexibility prevents the removal of the com- position. When the resist is to be removed after gilding, put the parts into warm oil or tepid turpentine, then into a very hot soap-water or alkaline solution; and, lastly, into fresh water. Scratch-brush and dry in warm, white wood sawdust. The holes of the pinions are cleansed and polished with small pieces of very white, soft wood, the friction of which is sufficient to restore the primitive lustre. 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." The silvering of fine copper wire is effected in an apparatus similar to that shown in Fig. 1 12, p. 21 1, a reservoir containing potassium cyanide solution for pickling the cleansed wire being added and placed in front of the silver bath. Lustre is im- parted to the silvered wire by drawing through a draw-plate. Further details will be found under " Gilding." DEPOSITION OF SILVER. 28 1 Incrustations with silver, gold, and other metals. By incrust- ing is understood the inlaying of depressions, produced by en- graving or etching upon a metallic body, with silver, gold, and other metals, such as Japanese incrustations, which are made by mechanically pressing the silver or gold into the depressions. Such incrustations, however, can also be produced by electro- deposition, the process being as follows : The design which is to be incrusted upon a metal is executed with a pigment of white-lead and glue-water or gum-water. The portion not cov- ered by the design is then coated with stopping-off varnish. The article is next placed in dilute nitric acid, whereby the pigment is first dissolved, and next the surface etched, which is allowed to progress to a certain depth. Etching being finished, the article is washed in an abundance of water and immediately brought into a silver or gold bath, in which by the action of the current the exposed places are filled up with metal. This being done, the " stopping-off " varnish is removed with benzine, the surface ground smooth, and polished. In this manner one article may be incrusted with several metals ; for instance, brass may be incrusted with copper, silver, and gold, and by oxidizing or coloring portions of the copper beautiful effects can be pro- duced. The principal requisites for these incrustations are manual skill and much patience ; expensive apparatus is not required, every skilled electro-plater being able to execute the work. Imitation of niel or nielled silvering. By nielling is under- stood the inlaying of designs, produced either by engraving or stamping, with a black mixture of metallic sulphides. The nielling powder is prepared by melting silver 20 parts by weight, copper 90 parts and lead 150 parts. To the liquid metallic mass add 26^ ozs. of sulphur and ^ oz. of sal ammoniac, quickly cover the crucible, and continue heating until the excess of sulphur is volatilized. Then pour the contents of the cruci- ble into another crucible, the bottom of which is covered about y^ inch deep with flowers of sulphur, cover the crucible and allow the mixture to cool. When cold bring the contents once more 282 ELECTRO-DEPOSITION OF METALS. to the fusing point and pour the fused mass in a thin stream into a bucket filled with water, whereby granulated metal is formed, which can be readily reduced in a mortar to a fine powder. This powder is mixed with sal ammoniac and gum- water to a thin paste. This paste is brought into the designs produced by engraving or stamping and after drying burnt in in a muffle. When cold any roughness is removed by grinding, and after polishing, a sharp black design in white silver is obtained. To imitate niel by electro-deposition the design is executed upon the surface with a pigment consisting of white lead and glue or gum-water. The portions which are to remain free are coated with " stopping-off " varnish, and the design is uncovered by etching with very dilute nitric acid. The article is then brought as the anode into dilute solution of ammonium sul- phide, while a small sheet of platinum connected to the nega- tive pole is dipped into the solution. Sulphide of silver being formed, the design becomes rapidly black gray, and after re- moving the " stopping-off " varnish with benzine, stands out in sharp contrast from the white silver. Upon brass nielling may be imitated by silvering the article and then engraving the design, by which the silver is removed and the brass uncovered. The article is then brought into the black bright dip, by which the uncovered brass is colored black while the silvered portions remain unchanged. If portions in relief are to be made black, the silvering is removed by grind- ing, the article dipped into cream of tartar solution and then brought into the black bright dip. This process is largely em- ployed by manufacturers of buttons when silvered buttons are to be supplied with the name of the firm and the quality number in black. Old (antique) silvering. To give silvered articles an antique appearance, coat them with a thin paste of 6 parts graphite, I red ochre, and sufficient spirits of turpentine. After drying, a gentle rubbing with a soft brush removes the excess of powder, and the reliefs are set off (discharged) by means of a rag dipped into alcohol. DEPOSITION OF SILVER. 283 A tone resembling antique silvering is also obtained by brush- ing the silvered articles with a soft brush moistened with very dilute alcoholic solution of chloride of platinum. In order to impart the old silver tinge to small articles, such as buttons, rings, etc., they are agitated in the above-mentioned paste, and then "tumbled" with a large quantity of dry sawdust until the desired shade is obtained. Many operators, at the present day, produce the antique silvering by beginning with the oxidizing process about to be described, and setting off the reliefs by means of a hard brush and pumice-stone, or Spanish white. This last process is almost exclusively used for metallic mountings of books and albums. Oxidized silver. This term is incorrect, as by it is under- stood not an oxidation, but a combination with sulphur or chlorine. Solution of pentasulphide of potassium (liver of sulphur of the shops) is generally used for the purpose. Im- merse the articles in a solution of 2.75 drachms of liver of sulphur and 5^ drachms of ammonium carbonate in I quart of water heated to 176 F., and allow them to remain until they have acquired the desired dark tone. Immediately after im- mersion the articles become pale gray, then darker, and, finally, deep black-blue. For coloring in this manner the silvering should not be too thin ; for articles with a very thick deposit of silver, solution of double the strength may be used. Very slightly silvered articles cannot be oxidized in this manner, as the bath would remove the silvering, or under the most favor- able circumstances produce only a gray color. If the operation is not successful, and the articles come from the bath stained or otherwise defective, dip them in a warm potassium cyanide solution which rapidly dissolves the silver sulphide formed. A yellow color is imparted to silvered articles by immersion in a hot concentrated solution of chloride of copper, rinsing and drying. Stripping silvered articles. When a silvering operation has failed, or the silver is to be stripped from old silvered articles, 284 ELECTRO-DEPOSITION OF METALS. different methods have to be used according to the nature of the basis-metal. Silvered iron articles are treated as the anode in potassium cyanide solution in water (1:20), the iron not being brought into solution by potassium cyanide. As cathode suspend in the solution a few silver anodes or a copper sheet rubbed with an oily rag ; the silver precipitates upon the copper sheet, but does not adhere to it. Articles, the basis of which is copper, are best stripped by immersion in a mixture of equal parts of anhydrous (fuming) sulphuric acid and nitric acid of 40 Be. This mixture makes the copper passive, it not being attacked while the silver is dissolved. Care must, however, be had not to introduce any water into the acids, nor to let them stand without being hermetically closed, since by absorbing moisture from the air they become dilute and may then exert a dissolving effect upon the copper. The fuming sulphuric acid may also be heated in a shallow pan of enameled cast-iron to between 300 and 400 F. Then at the moment of using it, pinches of dry and pulverized nitrate of potassium (saltpetre) are thrown into it, and the article, held with copper tongs, is plunged into the liquid. The silver is rapidly removed, while the copper or its alloys is but slightly corroded. According to the rapidity of the solution, fresh additions of saltpetre are made. All the silver has been dissolved when, after rinsing in water and dipping the articles into the cleansing acids, they pre- sent no brown or black spots, that is to say, when they behave like new. In this hot acid stripping proceeds more quickly than in the cold acid mixture, but the latter acts more uniformly. Determination of electro-deposited silvering. By applying to genuine silvering, a drop of nitric acid of 1.2 specific gravity, in which red chromate of potash has been dissolved to saturation, a red stain of chromate of silver is formed. According to Grager, this method may also be used, to a certain extent, for the recognition of other white metals which may be mistaken for silver. A drop of the mixture applied to German silver becomes brown, no red stain appearing after rinsing with water ; upon Britannia the drop produces a black stain ; zinc is etched DEPOSITION OF SILVER. 285 without a colored spot remaining behind ; upon amalgamated metals a brownish precipitate is formed, which does not adhere and is washed away by water; upon tin the drop also acquires a brownish color, and by diluting with water a yellow precipi- tate is formed ; upon lead a beautiful yellow precipftate is formed. Custom-house officers in Germany are directed by law to use the following process for the determination of genuine silver- ing: Wash a place on the article with ether or alcohol, dry with blotting paper, and apply to the spot thus cleansed a drop of a i to 2 per cent, solution of crystallized bisulphite of soda prepared by boiling 1.05 ozs. of sodium sulphite and 2.36 drachms of flowers of sulphur with O.88 oz, of water until the sulphur is dissolved, and diluting to I quart of fluid. Allow the drop to remain upon the article about ten minutes and then rinse off with water. Upon silver articles a full, round, steel- gray spot is produced. Other white metals and alloys, with the exception of amalgamated copper, do not show this phe- nomenon, there appearing at the utmost a dark ring at the edge of the drop. Amalgamated copper is more quickly colored and acquires a more dead-black color than silver. Recovery of silver from old silver baths, etc. Old solutions which contain silver in the form of a silver salt are easily treated. It is sufficient to add to them, in excess, a solution of common salt, or hydrochloric acid, when all the silver will be precipi- tated in the state of chloride of silver, which, after washing, may be employed for the preparation of new baths. For the recovery of silver from solutions which contain it as cyanide, the solutions may be evaporated to dryness, the residue mixed with a small quantity of calcined soda and potassium cyanide, and fused in a crucible, whereby metallic silver is formed, which, when the heat is sufficiently increased, will be found as a button upon the bottom of the crucible ; or if it is not desirable to heat to the melting-point of silver, the fritted mass is dissolved in hot water, and the solution containing the soda and cyanide quickly filtered off from the metallic silver. 286 ELECTRO-DEPOSITION OF METALS. The evaporation of large quantities of fluid, to be sure, is in- convenient, and requires considerable time. But the reducing process above described is without doubt the most simple and least injurious. According to the wet method the bath is strongly acidulated with hydrochloric acid, provision being made for the effectual carrying off of the hydrocyanic acid liberated. Remove the precipitated chloride of silver and cyanide of copper by filtra- tion, and, after thorough washing, transfer it to a porcelain dish and treat it, with the aid of heat, with hot hydrochloric acid, which will dissolve the cyanide of copper. The resulting chloride of silver is then reduced to the metallic state by mixing it with four times its weight of crystallized carbonate of soda and half its weight of pulverized charcoal. The whole is made into a homogeneous paste, which is thoroughly dried, and then introduced into a strongly heated crucible. When all the material has been introduced, the heat is raised to promote complete fusion and to facilitate the collection of the separate globules of silver into a single button at the bottom of the crucible, where it will be found after cooling. If granulated silver is wanted, pour the metal in a thin stream and from a certain height into a large volume of water. Still simpler is the reduction of the chloride of silver by pure zinc ; for this purpose suspend the chloride of silver in water, add hydrochloric acid, and place pure zinc rods or granulated zinc in the fluid. The zinc dissolving, metallic silver is sepa- rated, which is filtered off, washed, and dried. To precipitate the silver from silver solutions containing potassium cyanide it suffices to place a bright sheet of zinc in the solution, though the simultaneous use of a sheet of zinc and a sheet of iron is more suitable. While with the use of zinc alone the silver sometimes adheres firmly to the zinc, it always separates in a pulverulent form when zinc and iron are em- ployed. It is only necessary to wash the separated silver, which, as a rule, contains copper, and after drying to dissolve it, best in warm concentrated sulphuric acid. The solution is DEPOSITION OF GOLD. 287 diluted with water and the dissolved silver precipitated by means of strips of copper. The silver thus obtained is perfectly pure. If the content of copper is small, it may be removed from the silver precipitated with zinc by fusing with a small quantity of saltpetre and borax. CHAPTER X. DEPOSITION OF GOLD. GOLD is chiefly found in the metallic state, and generally alloyed with more or less silver, copper, and iron. The follow- ing analyses will serve to show the general composition of the native metal : Australia. California. Russia. "Wales. Gold 94-64 89.10 98.96 89.83 Silver 4.95 10.50 0.16 9.24 Copper .... 0.05 Iron 0.41 0.20 0.315 IOC.GO 99.80 99-S 2 99-7 Gold is one of the few metals possessing a yellow color ; pre- cipitated from its solution with green vitriol or oxalic acid, it appears as a brown powder without lustre, which on pressing with the burnisher acquires the color and lustre of fused gold. Pure gold is nearly as soft as lead, but possesses considerable tenacity. In order to increase its hardness when used for arti- cles of jewelry and for coinage it is mixed with silver or copper. The " fineness of gold," or its proportion in the alloy, is usually expressed by stating the number of carats present in 24 carats of the mixture. Pure gold is stated to be 24 carats ' fine ; " standard gold is 22 carats " fine ; " 18 carat gold is a mixture of 18 parts of gold and 6 of alloy. Gold is the most malleable and ductile of the metals ; it may be beaten out into leaves not ex- ceeding roWoth of a millimeter in thickness. When beaten 288 ELECTRO-DEPOSITION OF METALS. out into thin leaves and viewed by transmitted light gold ap- pears green ; when very finely divided it is dark red or black. The specific gravity of fused gold is 19.35, an d of precipitated gold powder from 19.8 to 20.2. Pure gold melts at about 2016 F., and in fusing exhibits a sea-green color. The melt- ing-points of alloyed gold vary according to the degree of fine- ness. Thus, 23 carat gold melts at 2012 F. ; 22 carat at' 2009; 20 carat at 2002; 18 carat at 1995; 15 carat at 1992; 13 carat at 1990; 12 carat at 1987; 10 carat at 1982; 9 carat at 1979; 8 carat at 1973; 7 carat at 1960. The fineness of gold may be approximately estimated by means of the touch-stone, a balsatic stone formerly obtained from Asia Minor, but now procured from Saxony and Bohemia. The sample of gold to be tested is drawn across the stone, and the streak of metal is treated with dilute nitric acid ; from the rapidity of the action and the intensity of the green color pro- duced due to the solution of the copper as compared with streaks made by alloys of known composition, the assayer is enabled to judge of the proportion of inferior metal which is present. Gold preserves its lustre in the air and is not acted upon by any of the ordinary acids. Nitric, hydrocholoric, or sulphuric acid by itself does not dissolve gold, but it dissolves in acid mixtures which develop chlorine, hence in aqua regia (nitro-hydrochloric acid). The gold found in commerce under the name of shell-gold or painter* s gold, which is used in painting and for repairing smaller defects in electro-gilding, is prepared by triturating waste in the manufacture of leaf gold with water, diluted honey or gum-water. Gold solution may also be precipitated with antimonic chloride. The resulting precipitate is triturated with barium hydrate, extracted with hydrochloric acid, and after washing, the gold powder is triturated with gum arabic solu- tion. Gold baths. Electro-gilding may be done with the aid of heat or in the cold, large objects being generally gilded in the cold bath, and smaller objects in the hot bath. The latter has DEPOSITION OF GOLD. 289 the advantage of requiring less current-strength, besides yield- ing deposits of greater density and uniformity and of sadder, richer tones. Baths for hot gilding work with a moderate con- tent of gold 11^2 to I2J^ grains of gold per quart while baths for cold gilding should contain not less than 54 grains per quart. ' Some authors for instance, Eisner, Briant, Selm, and others give the preference to baths prepared with potassium ferro- cyanide ; while others, like Elkington nnd Regnault, work with a solution of gold-salt and potassium bicarbonate ; and Bottcher, Leuchtenberg, and others recommend a solution of cyanide of gold in potassium cyanide. With proper treatment of the bath, good results may be obtained with either. However, the use of baths prepared with potassium ferrocyanide cannot be recom- mended on account of the secondary decompositions which take place during the operation of plating, and because the baths do not dissolve the gold anodes. In the following, only approved formulae for the preparation of gold baths will be given : I. Bath for cold gilding. Fine gold in the form of fulmin- ating gold 54 grains, 98 per cent, potassium cyanide 0.35 to 0.5 oz. (according to the current-strength used), water I quart. To prepare this bath, dissolve 54 grains of fine gold in aqua regia in a porcelain dish heated over a gas or alcohol flame, and evaporate the solution to dryness. Continue the heating until the solution is thickly fluid and dark brown, and on cooling congeals to a dark brown, foliated mass. Heating too strongly should be avoided, as this would cause decomposition and the auric chloride would be converted into aurous chloride, and eventually into metallic gold and escaping chlorine. The neutral chloride of gold prepared in this manner is dissolved in i pint of water and aqua ammonia added to the solution as long as a yellow-brown precipitate is formed, avoiding, how- ever, a considerable excess of aqua ammonia. The precipitate of fulminating gold is filtered off, washed, and dissolved in I quart of water containing 0.5 oz. of potassium cyanide in solu- 19 2QO ELECTRO-DEPOSITION OF METALS. tion. The solution is boiled, replacing the water lost by evaporation, until the odor of ammonia which is liberated by dissolving the fulminating gold in potassium cyanide disappears when it is filtered. Instead of dissolving the gold and pre- paring neutral chlorfde of gold by evaporating, it is more con- venient to use 108 grains of chemically pure neutral chloride of gold as furnished by chemical works, and precipitate the ful- minating gold from its solution. Too large an excess of potassium cyanide yields gold deposits of an ugly, pale color. When working with a more powerful current, the excess of potassium cyanide need only be slight; with a weaker current it must be larger. With 10 per cent, excess of free potassium cyanide, the most suitable current- strength is 3 volts. The fulminating gold should not be dried, as in this condition it is highly explosive, but should be immediately dissolved while in a moist state. For cold gilding, Roseleur recommends the following bath: II. Fine gold as neutral chloride of gold 0.35 oz., 98 per cent, potassium cyanide 0.7 oz., water I quart. Dissolve the gold-salt from 0.35 oz. of fine gold or about 0.7 oz. of neutral chloride of gold in y 2 pint of water, and the potas- sium cyanide in I y 2 pints of water, and after mixing the solu- tions boil for half an hour, The preparation of this bath is more simple than that of formula I., but the color of the gold deposit obtained with the latter is warmer and sadder than with the first. The high content of gold in the bath, prepared according to formula II., readily causes a red-brown gold de- posit, and hence special attention has to be paid to the regu- lation of the current. For those who prefer gold baths prepared with yellow prus- siate of potash instead of potassium cyanide, the following formnla for cold gilding is given: III. Yellow prussiate of potash (potassium ferrocyanide) 0.5 oz., carbonate of soda 0.5 oz.. fine gold (as chloride of gold or fulminating gold) ~ 75 grains, water I quart. DEPOSITION OF GOLD. 2QI To prepare the bath, heat the solutions of the yellow prussiate of potash and of the carbonate of soda in the water to the boil- ing-point, add the gold-salt, and boil ^ hour, or with the use of freshly precipitated fulminating gold, until the odor of am- monia disappears. After cooling, the solution is mixed with a quantity of distilled water corresponding to the water lost by evaporation, and filtered. This bath gives a beautiful bright gilding upon all metals, even upon iron and steel. Suitable current-strength 3.25 to 3.26 volts. Gold bath for hot gilding. IV. Fine gold (as fulminating gold) 15.4 grains, 98 per cent, potassium cyanide 77 grains, water I quart. This bath is prepared in the same manner as that according to formula I., from 15.4 grains of fine gold, which is converted into neutral chloride of gold by dissolving in aqua regia and evaporating; or dissolve directly 29.32 to 30.75 grains of chemically pure neutral chloride of gold in water, precipitate the gold as fulminating gold with aqua ammonia, wash the pre- cipitate, dissolve it in water containing the 'potassium cyanide, and heat until the odor of ammonia disappears, replacing the water lost by evaporation. This bath yields a beautiful sad gilding of great warmth. All that has been said in regard to the content of potassium cyanide in the bath prepared accord- ing to formula I. also applies to this bath. The temperature should be between 158 and 176 F., and the current-strength 2.0 to 2.5 volts. Roseleur recommends for hot gilding : V. Chemically pure crystallized sodium phosphate 2.11 ozs., neutral sodium sul- phide 0.35 oz., potassium cyanide 30.86 grains, fine gold (as chloride) 15.43 grains, distilled water I quart. If this bath is to serve for the direct gilding of steel, only [ 5.43 instead of 30.86 grains of potassium cyanide are to be used. Dissolve in a porcelain dish, with the aid of moderate heat, the sodium phosphate and sodium sulphide, and when the solution is cold, add the neutral chloride of gold prepared from 15.43 grains of gold= about 30.86 grains of ci- Vnercial chloride of ELECTRO-DEPOSITION OF METALS. gold, and the potassium cyanide ; for use, heat the bath to between 158 and 167 F. Conrad Taucher recommends the following formulae for hot gilding: VI. Sodium phosphate 14 ozs., sodium bisulphite 3^ ozs., sodium bicarbonate i ^ ozs., caustic potash i^ ozs., potas- sium cyanide 14 drachms, gold in the form of neutral chloride S^4 drachms, distilled water 10 quarts. With the exception of the chloride of gold, all the salts may be dissolved together. The solution, if necessary, is filtered and the gold solution added. The bath is used at between 122 and 140 F. It yields a very beautiful gilding, but requires a quite strong current for its decomposition. It is not suitable for the direct gilding of steel. VII. Yellow prussiate of potash (potassium ferrocyanide) 5*^ ozs., pure potassium carbonate i^ ozs., sal ammoniac 11^ drachms, gold in the form of neutral chloride 5^ drachms, water 5 quarts. Dissolve with the assistance of heat the first three salts, filter, and when cold add the chloride of gold. Then heat again and boil for half an hour, replacing the water lost by evaporation. Many electro-platers prepare the gold baths with the assist- ance of the electric current. For this purpose prepare a solu- tion of 3.52 ozs. of potassium cyanide (98 to 99 per cent.) per quart of water, and after heating to between 122 and 140 F. conduct the current of two Bunsen elements through two sheets of gold, not too small, which are suspended as electrodes in the potassium cyanide solution. The action of the current is inter- rupted when the solution is so far saturated with gold that an article immersed in it and connected to the negative pole in place of the other gold sheet is gilded with a beautiful warm tone. By weighing the sheet of gold serving as anode, the amount of gold which has passed into the solution is ascer- tained. According to English authorities, a good gold bath prepared according to this method should contain 3.52 ozs. of potassium cyanide and 0.7 oz. of fine gold per quart of water. DEPOSITION OF GOLD. 293 The only advantage of this mode of preparing the bath is that it excludes a possible loss of gold which may occur in dissolv- ing gold, evaporating the gold solution, etc., by breaking the vessel containing the solution. However, by using commercial chemically pure chloride of gold such loss is avoided, and the bath prepared according to the formulae given yields richer tones than a gold bath produced by electrolysis. Besides, the preparation of the gold bath with the assistance of the electric current can only be considered for smaller baths, since the sat- uration of a larger .volume of potassium cyanide solution re- quires considerable time, and the potassium cyanide is strongly decomposed by long heating. Management of gold baths. It is advisable to keep the con- tent of gold in the baths prepared according to the different formulae as constant as possible, which is best effected by the use of fine gold anodes. Insoluble platinum anodes are better liked in gilding than for all other electro-plating processes, partly because they are cheaper, and partly because they are recommended in most books on the subject. However, a bath which has become low in gold does not yield a beautiful gold color, and has to be frequently strengthened by the addition of chloride of gold, the preparation of which consumes time and causes expense, so that the use of gold anodes is the cheapest in the end. The employment of anodes of platinum strips or platinum wire may, perhaps, be advocated for coloring the de- posit, i. e.j for the purpose of obtaining certain tones of color when gilding in the hot bath. By allowing the platinum anode to dip only slightly in the bath a pale gilding is obtained, be- cause the current thereby becomes weaker ; by immersing the anode deeper the color becomes more yellow, and by immersing it entirely the tone becomes more reddish. However, instead of producing these effects of the current-strength by the anode, which requires the constant presence of the operator, it is better to obtain the coloration by means of the resistance board. By placing the handle upon " strong " a reddish gold tone is ob- tained, and by placing it upon "weak" a paler gold tone, while 294 ELECTRO-DEPOSITION OF METALS. the beautiful gold yellow lies in the middle between the two ex- tremes. However, since even with the use of gold anodes the content of gold in the bath is not entirely restored, the bath has after some time to be strengthened, which is effected by a solu- tion of fulminating gold or chloride of gold in potassium cyan- ide, according to the composition of the bath. As in the silvering baths, the excess of potassium cyanide in the gold baths is also partially converted into potassium carbo- nate by the action of the air, the heat, etc., and it is, therefore, advisable from time to time to add a small quantity of potas- sium cyanide. Gold baths for cold gilding are kept in vats of stoneware or enameled iron, or small baths in glass vats, which, to protect FIG. 121. them against breaking, are placed in a wooden box. Baths for hot gilding require enameled iron vats in which they can be heated by a direct fire, or better, by placing in hot water (water bath), or by steam. For small gold baths for hot gilding, a porcelain dish resting upon a short-legged iron tripod may be used. (Fig. 121.) Beneath the iron tripod is a gas burner supplied with gas by means of flexible India-rubber tubing con- nected to an ordinary gas burner. Across the porcelain dish DEPOSITION OF GOLD. 295 are placed two glass rods around which the pole-wires are wrapped. In heating larger baths in enameled vats over a direct fire it may happen that on the places most exposed to the heat the enamel may blister and peel off; it is, therefore, better to heat the baths in a water or steam bath. For this purpose have made a box of stout iron or zinc sheet about ^ inch wider and longer, and about 4 inches deeper than the enameled vat containing the gold bath. To keep the level of the water constant, the box is to be provided with a water inlet and overflow pipe. In this box place the vat so that its edges rest upon those of the box, and make the joints tight with tow. The water-bath is then heated over a gas flame or upon a hearth, the water lost by evaporation being constantly replaced, so that the enameled vat is always to half its height surrounded by hot water. For heating by steam the arrangement is the same, only a valve for the introduction and a pipe for the discharge of steam are substituted for the water inlet and everflow pipe. Execution of gilding. Like all other electro-plating opera- tions, it is advisable to execute gilding with an external source of current; that is, to use a battery or other source of current separated from the bath, and to couple the apparatuses as pre- viously described and illustrated by Figs. 52 and 54. To be sure, there are still gilders who gild without a battery or separate external source of current and obtain good results, the process being, as a rule, employed only in gilding small articles. The apparatus used for this purpose consists of a glass vessel containing the gold solution compounded with a large excess of potassium cyanide and a porous clay cell filled with very dilute sulphuric acid or common salt solution, which is placed in the glass vessel ; care should be taken to have the fluids in both vessels at the same level. Immerse in the clay cell an amalgamated zinc cylinder or zinc plate, to which a copper wire is soldered. Outside the cell this copper wire is bent downwards, and the article to be gilded, which dips in the gold solution, is fastened to it. In working with this apparatus there is always a loss of gold, since the gold solution penetrates 296 ELECTRO-DEPOSITION OF METALS. through the porous cell, and on coming in contact with the zinc is reduced by it, the gold being separated as black powder upon the zinc. In cleaning the apparatus this black slime has to be carefully collected and worked for fine gold. For the sake of greater solidity, only articles of silver and copper and its alloys should be directly gilded, while all other metals are best first brassed or coppered. Cleaning from grease and pickling is done in the same manner, as described on page 156. The preparation of the articles for gilding differs from that for silvering only in that the surfaces which later on are to appear with high lustre are not artificially roughened with emery, pumice, or by pickling, because, on the one hand, the gold deposit seldom needs to be made extravagantly heavy, and the rough surface formed would require more laborious polishing with the burnishers ; and, on the other, the gold de- posits adhere quite well to highly- polished surfaces, provided the current strength is correctly regulated, and the bath accu- rately composed according to one of the formulae given. Quick- ing the articles before gilding, which is recommended by some authors, is not necessary. The current-strength must, under no circumstances, be so great that a decomposition of water and consequent evolution of hydrogen on the objects take place, since otherwise the gold would not deposit in a reguline and coherent form, but as a brown powder. By regulating the current strength so that it just suffices for the decomposition of the bath, and avoiding a considerable surplus, a very dense and uniform deposit is formed ; and by allowing the object to remain long enough in the bath, a beautiful, dull gold deposit can be obtained in all the baths prepared according to the formulae given. It may, however, be mentioned that this mode of dull gilding is the most expensive, since it requires a very heavy deposit, and it will, therefore, be better to deaden the surface previous to gild- ing according to a process to be described later on. For gilding with cold baths two freshly filled Bunsen ele- ments coupled for tension suffice in almost all cases, while DEPOSITION OF GOLD. 297 for hot baths one element is, as a rule, sufficient, if the anode surface is not too small. The more electro- positive the metal to be gilded is, the weaker the current can and must be. Though gold solutions are good conductors and, therefore, the portions which do not hang directly opposite the anodes gild well, for the solid gilding of larger objects it is recom- mended to frequently change their positions except when they are entirely surrounded by anodes. The inner surfaces of hollow-ware, such as drinking-cups, milk pitchers, etc., are best gilded after freeing them from grease and pickling, by filling the vessel with the gold bath and suspending a current-carrying gold anode in the centre of the vessel, while the outer surface of the latter is brought in con- tact with the negative conducting wire. The lips of vessels are gilded by placing upon them a cloth rag saturated with the gold bath and covering the rag with the gold anode. For gilding in the cold, bath the process is as follows : The objects, thoroughly freed from grease and pickled (and if of iron, zinc, tin, Britannia, etc., previously coppered), are hung in the bath by copper wires, where they remain with a weak current until in about 8 or 10 minutes they appear uniformly gilded. At this stage they are taken from the bath, rinsed in a pot filled with water, which, after working for some time, is added to the bath to replace the water lost by evaporation, and brushed with a fine brass scratch-brush and tartar solution. They are then thoroughly rinsed, again freed from grease by brushing with lime-paste and then returned to the bath, where they remain until they have acquired a deposit of sufficient thickness. If it is intended to give them a very heavy deposit, it is advis- able to scratch-brush them several times with the use of tartar or its solution. For gilding by weight the same plan as given for silvering (p. 260) is pursued. For gilding with the hot bath the operations are the same, with the exception that a weaker current is introdued into the bath and the time of the gilding process shortened. Frequent 298 ELECTRO-DEPOSITION OF METALS. scratch-brushing also increases the solidity of the deposit and prevents the premature turning to a dead brown-black. Since in hot gilding more gold than intended is readily deposited, it is especially advisable to place a resistance board in the circuit, as otherwise the operator must remain standing alongside of the bath and regulate the effect of the current by immersing the anodes more or less. With a somewhat considerable excess of potassium cyanide, and if the objects to be gilded are not rapidly brought in con- tact with the current-carrying object rod, hot gold baths cause the solution of some metal. Therefore, when silver or silvered objects are constantly gilded in them they yield a somewhat greenish gilding in consequence of the absorption of silver, or a reddish gilding due to the absorption of copper, if copper or coppered articles are constantly gilded in them. Hence, for the production of such green or reddish color, gilding baths which have thus become argentiferous or cupriferous may be advantageously used. In order to obtain a deposit of green or red gold with fresh baths, the tone-giving addition of metal must be artificially effected, as will immediately be seen. If, however, such extreme tones are not desired, the content of gold in the baths may be exhausted for preliminary gilding with the use of platinum anodes, the sad gold color being then given in a freshly prepared bath. The gold deposits are polished, in the same manner as silver deposits, with the burnisher and red ochre, and moistening with solution of soap, decoction of flaxseed, or soap-root, etc. Red gilding. In order to obtain a red gold with the formulae given, a certain addition of cyanide of copper dissolved in potas- sium cyanide has to be made to them. The quantity of such addition cannot be well expressed by figures, since the current- strength with which the articles are gilded exerts considerable influence. It is best to triturate the cyanide of copper in a mortar, to a paste with water, and add of this paste to a mode- rately concentrated potassium cyanide solution as long as cyanide of copper is dissolved. Of this copper solution add, DEPOSITION OF GOLD. 299 gradually and in not too large portions, to the gold solution until, with the current-strength used, the gold deposit shows the desired red tone. The absorption of copper by the bath may also be effected by replacing the gold anodes by copper anodes and circulating the current (suspending a few gold anodes to the object rod). The direct addition of cyanide of- copper is, however, preferable. For the determination of the content of copper required for the purpose of obtaining a beautiful red gold, a bath for hot gilding which contained 10.8 grains of gold per quart was com- pounded with a solution of cyanide of copper in potassium cyanide with 1 .08 grains content of copper. The tone of the gilding, which previously was pure yellow, immediately passed into a pale red gold. By the further addition of 1.08 grains of copper a fiery red gold tone was obtained, while a third addi- tion of 1. 08 grains of copper yielded a color more approach- ing that of copper than of gold. These experiments show that 20 per cent, of copper of the weight of gold contained in the bath seems to be the most suitable proportion for obtain- ing a beautiful red gold. Green gilding. To obtain a greenish gilding, solution of cyanide or chloride of silver in potassium cyanide has to be added to the gold bath. It is not easy to prepare greenish gilding of a pleasing color, and to obtain it the current-strength must be accurately proportioned to the object-surface, since with too weak a current silver predominates in the deposit, the gilding then turning out whitish, while too strong a current de- posits too much gold in proportion to silver, the gilding becoming yellow, but not green. Rose-color gilding may be obtained by the addition of suit- able quantities of copper and silver solution, but such colora- tion requires much attention and thought. Dead gilding. As previously mentioned, a beautiful dead gold deposit may be obtained by the use of any of the formulae given and a correctly regulated current, and allowing sufficient length of time for gilding ; but the heavy deposit of 300 ELECTRO-DEPOSITION OF METALS. gold required for this process makes it too expensive, and it is therefore advisable to produce dead gilding without excessively heavy deposits by previous deadening of the basis-surface. The process of graining has already been described on p. 277 ; another method is to deaden the first thin deposit of gold with the deadening scratch-brush, and then to give a second deposit of gold, which also turns out dead upon the deadened surface. However, this operation of deadening with the scratch-brush requires considerable skill, and it is therefore best to deaden the surface according to one of the following methods: For this purpose, the mixture of I volume of saturated solu- tion of bichromate of potash, and 2 volumes of concentrated hydrochloric acid, mentioned on p. 156, may be used. Brass articles are allowed to remain in the mixture several hours, and are then quickly drawn through the bright-dipping bath ; Or, by depositing upon the articles a coating of frosted silver and then gilding in a good gold bath. Unfortunately, this method is somewhat expensive, and the burnished parts are greenish. Moreover, the intermediary coat of silver is easily affected by sulphurous gases, the gilding being thereby blackened. More advantageous is the process of providing the articles with a dead copper coating in the acid galvanoplastic copper bath, then quicking them, and finally gilding. This gilding is very handsome in lustre and color. Dead gilding on zinc. By the following process of deposit- ing gold on zinc, effects similar to those of fire-gilding on bronze are produced. The zinc is first heavily coppered in one of the copper baths previously given, and is then brought into a silver- ing bath (with use of a battery) or into an acid copper bath (see " Galvanoplasty "), according to whether deadening is to be effected with silver or copper. In deadening in the acid copper bath care should be taken that the suspending wires are in contact with the object-rod before immersing the coppered zinc object in the bath. However, this process of coppering zinc in the acid copper bath is a very delicate operation, it being DEPOSITION OF GOLD. 3OI requently observed that even with an apparently very heavy coppering in the electro-coppering bath, brownish-black spots appear on the objects when brought into the acid bath, the copper being deposited on these spots in a pulverulent form by the contact of the acid bath with the zinc. If this is observed, the objects have to be immediately taken from the bath, and after thorough scratch-brushing again thoroughly and quickly coppered in the electro-coppering bath before returning them to the acid copper bath. It may be recommended, first to provide the coppered zinc objects with a thin coat of nickel, and then to copper them in the acid copper bath. When the deposit seems of sufficient thickness, the zinc is washed in a large quantity of water, drawn through a weak solution of mercurous nitrate, and brought into a hot gilding bath composed as follows: Water 10 quarts, sodium phosphate 21 ozs., sodium bisulphite 3^ ozs., potassium cyanide iij{ drachms, gold (in the form of chloride) 5^ drachms. At first quite a strong current is used, which is gradually re- duced up to the moment when the object is taken from the bath. Coloring of the gilding. It has been frequently mentioned that the most rational and simple process of giving certain tones of color to the gilding is by means of a stronger or weaker current. Many operators, however, cling to the old method of effecting the coloration by gilder's wax or brushing with certain mixtures, and for this reason this process, which is generally used for coloring fire-gilding, shall be briefly mentioned. To impart to the gold-deposit a redder color, the gilding-wax is prepared with a greater content of copper, while for greenish gilding more zinc-salt is added. There are innumerable re- ceipts for the preparation of gilding-wax, nearly every gilder having his own receipt, which he considers superior to all others. Only two formulae which yield good results will here be given, one (I.) for reddish gilding and one (II.) for greenish gilding. I. Wax 12 parts by weight, pulverized verdigris 8, pulver- ized sulphate of zinc 4, copper scales 4, borax I, pulverized bloodstone 6, copperas 2. 302 ELECTRO-DEPOSITION OF METALS. II. Wax 12 parts by weight, pulverized verdigris 4, pulver- ized sulphate of zinc 8, copper scales 2, borax I, pulverized bloodstone 6, copperas 2. Gilder's wax is prepared as follows: Melt the wax in an iron kettle, add to the melted mass, with constant stirring, the other ingredients, pulverized and intimately mixed, in small portions, and stir until cold, so that the powder cannot settle on the bottom or form lumps. Finally, mould the soft mass into sticks about % inch in diameter. The operation for applying the gilder's wax is as follows : Coat the heated gilded articles uniformly with the wax and burn off over a charcoal fire, frequently turning the articles. After the extinguishment of the wax flames, plunge the articles into water, scratch-brush with wine-vinegar, dry in sawdust, and polish. , To give gilded articles a beautiful, rich appearance, the fol- lowing process may also be used : Mix 3 parts by weight of pulverized alum, 6 of saltpetre, 3 of sulphate of zinc, and 3 of common salt, with sufficient water to form a thinly-fluid paste. Apply this paste as uniformly as possible to the articles by means of a brush, and after drying, heat the coating upon an iron plate until it turns black ; then wash in water, scratch- brush with wine-vinegar, dry, and polish. According to a French receipt^ the same result is attained by mixing pulverized blue vitriol 3 parts by weight, verdigris 7, sal ammoniac 6, and saltpetre 6, with acetic acid 31 ; immers- ing the gilded articles in the mixture or applying the latter with a brush ; then heating the objects upon a hot iron plate until they turn black, and, after cooling, pickling in concen- trated sulphuric acid. Some gilders improve bad tones of gilding by immersing the articles in dilute solution of nitrate of mercury until the gilding appears white ; the mercury is then evaporated over a flame and the articles are scratch-brushed. Others apply a paste of pulverized borax and water, heat until the borax melts, and then quickly immerse in dilute sulphurfc acid. DEPOSITION OF GOLD. 303 Incrustations with gold are produced in the same manner as incrustations with silver described on p. 281. Gilding of metallic wire and gauze, Fine wire of gilded copper and brass is much used in the manufacture of metallic fringes and lace, for epaulettes and other purposes. The fine copper and brass wires being drawn through the draw-irons and wound upon spools by special machines, and hence not touched by the hands, freeing from grease may, as a rule, be omitted. The first requisite for gilding is a good winding machine, which draws the wires through the gold bath and FIG. 122. wash boxes, and further effects the winding of the wire upon spools. The principal demand made in the construction of such a machine is that by means of a simple manipulation a great variation in the speed with which the wire or gauze passes through the gold bath can be obtained. This is neces- sary in order to be able to regulate the thickness of the gild- ing by the quicker or slower passage of the wire. A machine well adapted for this purpose is that constructed by J. W. Spaeth and shown in Fig. 122. 304 ELECTRO-DEPOSITION OF METALS. The variation in the passage of the wire is attained by the two friction-pulleys F, which sit upon a common shaft with the driving-pulley, R, and transmit their velocity by means of the friction-pistons KK 1 to the friction-pulley F t which is firmly connected to the belt-pulley R driving the spool spindle. Since by a simple device the pistons K and K' may be shifted, it is clear that the transmission of the number of revolutions from F \.o F is dependent on the position of the friction pistons K and K' ', and that the velocity will be the greater the shorter the distance they are from the centre of friction-pulleys F and F. In order that the friction between F, K, and F may always be sufficient for the transmission of the motion, even when the pistons are worn, four weights, G, are provided, which press the above-mentioned parts firmly against each other. In front of each spool of this machine is inserted a small enameled iron vat which contains the gold bath, and is heated by a gas flame to about 167 F. Between this bath and the winding machine is another small vat with hot water in which the gilded wire is rinsed. The wires unwind from a reel placed in front of the gold baths, run over a brass drum which is connected to the negative FIG. 123. pole of the source of current, and transmits the current to the wires ; the dipping of the wires into the gold bath is effected by porcelain drums, which are secured to heavy pieces of lead placed across the vats as shown in Fig. 123. The gilded wire being wound upon the spools of the winding machine, these spools are removed and thoroughly dried in the drying cham- ber. The wire is then again reeled off on to a simple reel, in doing which it is best to pass it through between two soft pieces of leather to increase its lustre. DEPOSITION OF GOLD. 305 The most suitable gold bath is that prepared according to formula IV. ; the current-strength should be from 6 to 8 volts, which will produce a deposit of sufficient thickness even with the wire passing at the most rapid rate through the bath. Gilding by contact, by immersion, and by friction. For contact gilding by touching with zinc, formulae I., II., IV., and V., 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: VIII. Fine gold as chloride of gold 54 grains, yellow prussiate of potash I oz., potash I oz., common salt I oz., water I quart. The bath is prepared as given for formula III. ; for use, heat it to boiling. Gilding by contact is done the same way as silvering by con- tact. The points of contact must be frequently changed, since in the gold bath intense stains are still more readily formed than in the silver bath. For gilding by contact, Conrad Taucher recommends the fol- lowing bath : Distilled water 10 quarts, sodium or potassium pyrophosphate 28 ozs., prussic acid 4^ drachms, crystallized chloride of gold 13 j drachms. To prepare the bath, bring into a porcelain vessel or into a dish of enameled cast-iron 9 quarts of distilled* water and add the 28 ozs. of pyrophosphate, stirring constantly with a glass rod. Then heat, and when solution is complete filter and set aside to cool. While filtering the solution, the chloride of gold is prepared by bringing into a small glass flask 5 j drachms of fine rolled gold, 14 drachms of pure hydrochloric acid, and Sy^ drachms of pure nitric acid. Apply a gentle heat to the bottom of the flask. In a few seconds vigorous effervescence accompanied * The use of distilled water is necessary, otherwise the lime salts contained in ordinary water would decompose a portion of the pyrophosphate. 20 306 ELECTRO-DEPOSITION OF METALS. by the evolution of orange-red vapors takes place, and the gold in a few minutes dissolves to a reddish-yellow fluid. To evapo- rate an excess of acids, which if brought into the bath might cause serious disturbances and even render the bath entirely useless, the flask is placed upon a~piece of sheet-iron provided in the centre with a hole about o.n inch in diameter, and heated upon a stove or over a spirit lamp. When no more vapors escape and the solution has become thickly-fluid and has acquired an intense hyacinth-red color, remove the flask from the fire by means of wooden pincers and let cool. If prop- erly prepared, the chloride of gold then congeals to an aggre- gate of saffron-yellow acicular crystals. If the color of the latter is red, too much heat has been applied. Such chloride of gold is very suitable for the preparation of electro-gilding baths, but if it is to be used for contact gilding a small quantity of the above-mentioned two acids has to be added, and, after heating, the mass has to be again evaporated. It frequently happens that by careless manipulation the gold is "burnt," i. e., the auric chloride is decomposed by too long, continued heating and is converted into insoluble aurous chloride, or even into pulverulent metallic gold. If such is the case, the treatment with the above-mentioned mixture of acids has to be repeated. The object of the perforated piece of sheet- iron on which the flask is placed for the purpose of evaporating the solution is to prevent the sides of the flask from being heated too strongly, as otherwise the thin layers of chloride of gold solution might be decomposed. In practice porcelain capsules which are heated in a sand bath are generally used for dissolving gold. Fig. 124 shows such a capsule with glass funnel in a sand bath over a gas stove. The purpose of the glass funnel is to prevent any fluid from being thrown from the capsule at the moment of the effer- vescence caused by the action of the acids upon the metal. The cold crystallized chloride of gold in the flask or the cap- sule is now dissolved in a small quantity of distilled water, solution being effected almost immediately. The solution is DEPOSITION OF GOLD. 3O/ poured upon a filter of filtering paper in a glass funnel placed upon a clean bottle. A small piece of paper should be inserted between the funnel and the neck of the bottle, so that the air can escape from the latter and the fluid run off from the filter. FIG. 124. The object of filtering is to separate the small quantity of chloride of silver formed from the little silver which is present even in the purest commercial gold. To bring all the gold into the bath, repeatedly wash the bottle and the filter with a small quantity of distilled water. Now mix the cold solution of the pyrophosphate and that of the chloride of gold by pouring the latter graeually into the former and stirring with a glass rod. Then add the 4^ drachms of prussic acid and heat to the boiling point, when the bath is ready for use. When mixed cold the bath has a yellow or yellow-greenish color, which disappears as the temperature rises. However, the fluid sometimes becomes currant-red or violet, which indicates that it contains too little prussic acid. This is remedied by adding drop by drop prussic acid until the fluid is entirely dis- colored. Great care must, however, be exercised in adding the acid, as on excess of it renders the gilding pale. By following the directions above given, the bath is very suit- 308 ELECTRO-DEPOSITION OF METALS. able for producing a beautiful yellow gilding on objects previ- ously thoroughly cleansed. The articles should be passed through a very weak solution of mercurous nitrate, otherwise the gilding shades and becomes reddish. The articles to be gilded must be constantly moved in the bath ; they are sus- pended to hooks or brought into the bath in dipping baskets of stoneware or brass. Gilding is finished in a few seconds. The articles are then washed in clean water, dried in dry and warm sawdust, and if necessary, immediately polished. By neglecting the precautionary measures given above, the gilding sometimes appears tarnished and dissimilar in tone It is then colored or treated with the so-called matt for gilded articles. For this purpose melt equal parts of the following salts in their water of crystalization at about 212 F. : Ferrous sulphate (green vitriol), zinc sulphate (white vitriol), alum, and salt- petre. Thoroughly wet every portion of the defective gilding by turn- ing the articles about in this mixture. Then place them in the centre of a cylindrical stove, in which the coal burns between the sides and a cylindrical grate, so that the entire heat radiates toward the empty space in the centre. The salts melt and then get into a fiery flux, the entire mass acquiring a dull earthen color. When on touching the articles with the moistened finger a slight hissing noise is heard, the temperature is suffi- ciently high and the articles are thrown into weak starch-water acidulated with sulphuric acid. The coating of salts dissolves immediately and the gilding presents a beautiful warm and uni- form appearance. This operation can, of course, only be exe- cuted if the entire article has been gilded. Baths for gilding by dipping. The following two formulas have stood the test : I. Crystalized sodium pyrophosphate 2.82 ozs., 12 per cent, prussic acid 4.51 drachms, crystalized chloride of gold 1.12 drachms, water I quart. Heat the bath to the boiling point, DEPOSITION OF GOLD. 309 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 mercury (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 rapidly decomposing, and consequently can seldom be completely exhausted. In this respect the following formula answers much better : II. Crystalized sodium phosphate 2.82 drachms, chemically pure caustic potash 1.69 drachms, chloride of gold 0.56 drachm, 98 per cent, potassium cyanide 9.03 drachms, water I quart. Dissolve the sodium phosphate and caustic potash in y^ of the water, and the potassium cyanide and chloride of gold in the remaining ^, and mix both solutions. Heat the solution to the boiling point. This bath can be almost entirely exhausted, it not being decomposed by keeping. Should the bath become weak, add about 2^ drachms of potassium cyanide, and use it for preliminary dipping until no more gold is reduced. To complete gilding, the objects subjected to such preliminary dipping are then immersed for a few seconds in a freshly-prepared bath of the composition given above. The layer of gold formed is in all cases very thin, the amount of gold deposited corresponding to the quantity of basis-metal which has been dissolved. III. One of the best directions for gilding without the use of a current is, according to the " Edelmetallindustrie," as follows : Prepare a solution of gold in aqua regia (2 parts hydrochloric acid and I part nitric acid). The solution of the gold is effected in a porcelain dish, best in a sand or water bath, whereby heavy brown acid vapors of hyponitrous acid are evolved. When all is dissolved allow the acid to evaporate until the fluid has acquired a deep brown color and no more acid vapors arise. Then, after cooling, dilute the solution with water and keep it in a bottle for future use. Next dissolve in the bath 6^ drachms of potassa aad nj^ drachms of sodium 310 ELECTRO-DEPOSITION OF METALS. phosphate, and add enough gold solution that the bath con- tains about 2j drachms of gold. To this bath, containing about 8 to 10 quarts of fluid, add careiully, with constant stirring, I ^ ozs. of potassium cyanide, and then let it thor- oughly boil for some time. After cooling the bath to about 176 or 158 F., suspend the articles in it and keep the bath at this temperature. The bath only requires an occasional addi- tion of gold solution (when the gilding becomes gray or dirty), or of potassium cyanide (when the gilding becomes foxy), and, with proper treatment, can be used for a long time. Gilding of porcelain, glass, etc. The pyrophosphate baths given above may be advantageously employed for gilding porcelain, glass, stoneware, etc., the process being as follows : Neutral platinic chloride is intimately triturated with enough lavender oil to form a thin syrup. Of this preparation a scarcely perceptible film is applied by means of a small brush to the article to be ornamented. When dry, the article is heated in a muffle to a dark red heat. At this temperature the essen- tial oil partially volatilizes, while another portion is decom- posed, and reduces by its hydrogen the platinic chloride to metallic platinum, the result being a coating of metal of a finely polished appearance. When cold the article is immediately drawn through nitric acid, which does not attack the platinum, but removes any impurities which might make its surface dull. The article is then washed in a large quantity of water, wrapped with fine brass wire in such a manner that the wire touches the platinized places at many points, and is then brought into the gold bath. In a few minutes the platinum is coated with a beautiful smooth film of gold, which adheres well, and only re- quires rubbing with chamois. By this method the expensive work of polishing is rendered unnecessary, which with articles having many depressed places is besides almost impossible. If the gilding is too red, add to the bath a few drops of the double cyanide of potassium and silver. Gilding by friction. This process is variously termed gilding DEPOSITION OF GOLD. 311 with the rag, with the thumb, with the cork. It is chiefly em- ployed upon silver, though sometimes also upon brass and cop- per. The operation is as follows: Dissolve 1.12 to 1.69 drachms of chloride of gold in as little water as possible, to which has previously been added 0.56 drachm of saltpetre. Dip in this solution small linen rags, and, after allowing them to drain off, dry them in a dark place. These rags saturated with gold solution are then charred to tinder at not too great a heat, whereby the chloride of gold is reduced, partially to protochloride and partially to finely divided metallic gold. This tinder is then rubbed in a porcelain mortar to a fine uni- form powder. To gild with this powder, dip into it a charred cork moistened with vinegar or salt water and rub, with not too gentle a pres- sure, the surface of the article to be gilded, which must be previously cleansed from adhering grease. The thumb of the hand may be used in place of the cork, but in both cases care must he had not to moisten it too much, as otherwise the powder takes badly. After gilding the surface may be care- fully burnished. For gilding by friction a solution of chloride of gold in an excess of potassium cyanide may also be used, after thickening the solution to a paste by rubbing in whiting. The paste is applied to the previously zincked metals by means of a cork, a piece of leather, or a brush. Martin and Peyraud, the origina- tors of this method, describe the operation as follows : Articles of other metals than zinc are placed in a bath consisting of concentrated solution of sal ammoniac, in which has been placed a quantity of granulated zinc. The articles are allowed to boil a few minutes, whereby they acquire a coating of zinc. For the preparation of the gilding composition, dissolve 11.28 drachms of chloride of gold in a like quantity of 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 pul- verized tartar that a paste is formed which can *be readily ap- 312 ELECTRO-DEPOSITION OF METALS. plied with a brush to the article to be gilded. When the arti- cle 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. Fire or mercury gilding. Before the introduction of electro- plating, nearly all substantial gilding was effected by this pro- cess. However, the cost is much greater, the execution of the process presenting many difficulties, and besides the workman is constantly exposed to the very injurious mercurial vapors. The resulting gilding, however, is distinguished by great solidity. The execution of fire gilding begins with the preparation of the amalgam of gold. For this purpose put a weighed quantity of fine gold in a crucible and heat to dull redness. The re- quisite proportion of mercury, 8 parts to I of gold, is now added, and the mixture is stirred with a slightly crooked iron rod, the heat being kept up until the gold is entirely dissolved by the mercury. Pour the amalgam into a small dish about 3 parts filled with water, and work about with the fingers under the water to squeeze out as much of the excess of mercury as possible. To facilitate this the dish is slightly inclined, to allow the superfluous mercury to flow from the mass, which soon ac- quires a pasty condition capable of receiving the impression of the fingers. Afterward squeeze the amalgam in a chamois leather bag, by which a further quantity of mercury is liberated. The amalgam, which remains after this final treatment, consists of about 33 parts of mercury and 57 parts of gold in 100 parts. The mercury which is pressed through the bag retains a good deal of gold, and is employed in preparing fresh batches of amalgam. It is important that the mercury employed should be pure. To apply the amalgam, a solution of nitrate of mercury is em- ployed which is prepared by dissolving in a glass flask 100 parts of mercury in no parts of nitric acid of specific gravity 1.33, gentle heat being employed to assist the chemical action. The red fumes given off must be allowed to escape into the chimney, since they are very deleterious when inhaled. When DEPOSITION OF GOLD. 313 the mercury is all dissolved the solution is to be diluted with about 25 times its weight of distilled water, and bottled for use. The pasty amalgam is spread with the blade of a knife upon a hard, flat stone. The article, after being well cleaned and scratch- brushed, is treated as follows: Take a small scratch- brush, formed of stout brass wire, dip in the solution of nitrate of mercury, then draw over the amalgam ; pass the brush care- fully over the surface to be gilded, repeatedly dipping the brush in the mercurial solution and drawing it over the amal- gam until the entire surface is uniformly and sufficiently coated. Then rinse the article well, and dry. The next operation is the evaporation of the mercury. For this pur- pose a charcoal fire, resting upon a cast-iron plate, has been generally adopted, a simple hood of sheet-iron being the only means of protection from the injurious effects of the mercurial vapors. When the amalgamated article is rinsed and dried, it is exposed to the glowing charcoal, turned about and heated by degrees to the proper point, then it is withdrawn from the fire by means of long pincers or tongs. The article is then taken in the left hand, which should be protected with a leather glove, turned over the fire in every direction, and while the mercury is volatilizing the article should be struck with a long- haired brush to equalize the amalgam coating and force it upon such parts as may appear to require it. When the mercury has become entirely volatilized the gilding has a dull, greenish- yellow color. If any bare places are apparent, they are touched up with amalgam and the article is again submitted to the fire, care being taken to expel the mercury gradually. The article is then well scratch-brushed. When it is of a pale greenish color, heat it again to expel any remaining mercury, when it acquires the orange-yellow of fine gold. If required to be bright, it is burnished in the ordinary way. If the gild- ing is to be dead, secure the article by means of iron wire to the end of an iron rod and coat it with a hot paste consist- ing of saltpetre, common salt, and alum ; then expose the article to a bright fire, turning it in every direction until the 3 14 ELECTRO DEPOSITION OF METALS. coat of the mixture fuses and begins to run off; then remove the article from the fire and throw it in a wooden vat contain- ing a large quantity of water. The coat of salts covering the article is immediately dissolved, and the gilding presents a beautiful dead appearance. To stand this process of deadening the article must be well gilded, especially, as frequently hap- pens, if the operation does not succeed the first time. Red streaks are often observed on otherwise successful gild- ing. These streaks are caused by the iron wire which has been wrapped round the article. They disappear by plunging the article in dilute nitric acid, or, still better, in pure hydro- chloric acid. For the sake of completeness, a method of gilding which gives to some parts of the article a lustrous and to others a dead appearance may here be mentioned. It is a combination of fire-gilding with electro-deposition, the dead places being pro- duced by the former operation and the lustrous places by the latter. The operation is as follows : The places which are to be dead are first gilded with amalgam, heated, scratch-brushed and raised. The entire article is then gilded with the assistance of the battery, no attention being paid to any gold depositing upon the surfaces already gilded. The entire surface is then carefully scratch-brushed, and the elecltro-gilded surfaces are next coated with a paste of flake-white, water and glue, and then with a thick paste of clay, the fire-gilded surfaces remaining free. The whole is then allowed to dry, when the fire-gilded surfaces are deadened by being treated, as above described, with a hot paste of saltpetre, common salt, and alum. The coatings of flake-white and clay are then dissolved by means of water acidulated with hydrochloric acid. The only purpose of these coatings is to prevent a too intense action of the heat upon the electro-gilded portions. The latter, if necessary, are then again scratch-brushed, which must, however, be done with the greatest care to avoid injury to the dead portions. The article is finally polished. The following process, however, is better and more con- venient: DEPOSITION OF GOLD. 315 The surfaces which are to remain dead are first gilded and deadened, and then coated with varnish. When dry the article is pickled ; the acid does not attack the varnished surfaces. The object is then brought into the electro-gilding bath, which also does not attack the varnish. When the desired shade of gold has been obtained, the article is taken from the bath and the varnish removed by means of benzine. The article is then washed in a warm potassium cyanide solution, next in boiling water, and finally dried. The dead gilding, no matter by which process it may have been produced, is only suitable for arti- cles not exposed to friction, a slight touch with the fingers being sufficient to deprive it of its delicate lustre. Old dead gilding may be improved by boiling with potash and washing in dilute sulphuric or nitric acid. This suffices for the removal of stains caused by grease, smoke, or dust. If, however, the gilding is worn off, the article has to be scratch- brushed and regilt. Du Fresne gives a method of gilding, which is also a com- bination of fire-gilding with electro-deposition. It is executed as follows : The articles are galvanized with the assistance of the current, in a mercurial solution consisting of cyanide of mercury in potassium cyanide, with additions of carbonate and phosphate of soda, then gilded in an ordinary gilding bath, next again coated with mercury, then again gilded, and so on, until a de- posit of sufficient thickness is obtained. The mercury is then evaporated over glowing coals, and the articles, after scratch- brushing, are burnished. According to another process, the articles are gilded in a bath consisting of 98 per cent, potassium cyanide 1.2 ozs., cyanide of gold 92^ grains, cyanide of mercury 92^ grains, distilled water I quart, a strong current being used. The articles being sufficiently gilded, the mercury is evaporated, the articles scratch-brushed and finally polished. Removing gold from gilded articles " Stripping." Gilded articles of iron and steel are best stripped by treating them as 3l6 ELECTRO-DEPOSITION OF METALS. the anode in a solution of from 2 to 2^ ozs. of 98 per cent, potassium cyanide in I quart of water, and suspending a copper plate greased with oil or tallow as the cathode. Gilded silver- ware is readily stripped by heating to glowing and then im- mersing in dilute sulphuric acid, whereby the layer of gold cracks off, the glowing and subsequent immersion in dilute sulphuric acid being repeated until all the gold is removed. Before glow- ing and immersing in dilute sulphuric acid, the articles may first be provided with a coating of a paste of sal ammoniac, flowers of sulphur, borax, and nitrate of potash, which is allowed to dry. On the bottom of the vessel containing the dilute sulphuric acid the gold will be found in laminae and scales, which are boiled with pure sulphuric acid, washed, and finally dissolved in aqua regia, and made into chloride of gold or fulminating gold. To strip articles of silver, copper, or German silver which will- not bear glowing, the solution of gold may be effected in a mix- ture of I Ib. of fuming sulphuric acid, 2.64 ozs. of concentrated hydrochloric acid, and 1.3 ozs. of nitric acid of 40 Be. Dip the articles in the warm acid mixture and observe the pro- gressive action of the mixture by frequently removing the articles from it. The articles to be treated must be perfectly dry before immersing in the acid mixture, and care must be had to preserve the latter from dilution with water in order to prevent the acids from acting upon the basis-metal. Determination of genuine gilding. Objects apparently gilded are rubbed upon the touchstone, and the streak obtained is treated with pure nitric acid of 1.30 to 1.35 specific gravity. The metal contained in the streak thereby dissolves, and as far as it is not gold disappears, while the gold remains behind. The stone should be thoroughly cleansed before each operation, and the streak should be made not with an edge or a corner of the object to be tested, but with a broader surface. If no gold remains upon the stone, but there is, nevertheless, a suspicion of the article being slightly gilded, proceed with small articles as follows : Take hold of the article with a pair of tweezers, and after washing it first with alcohol, and then with ether, . and DEPOSITION OF GOLD. 317 drying upon blotting paper, pour over it in a test glass, cleansed with alcohol or ether, according to the weight of the article, 0.084 to 5.64 drachms of nitric acid of 1.30 specific gravity free from chlorine. The article will be immediately dissolved, and if it has been gilded never so slightly, perceptible gold spangles will remain upon the bottom of the glass. Recovery of gold from gold baths, etc. To recover the gold from old cyanide gilding baths, evaporate the bath to dryness, mix the residue with litharge, and fuse the mixture. The gold is contained in the lead button thus obtained. The latter is then dissolved in nitric acid, whereby the gold remains behind in the form of spangles. These spangles are filtered off and dissolved in aqua regia. The following method is used for the recovery of gold by the wet process: The bath containing gold, silver, and copper is acidulated with hydrochloric acid, which causes a disengage- ment of hydrocyanic acid. This gas is extremely poisonous, for which reason the operation should be carried on in the open air or where there is a good draught or ventilation to carry off the fumes. A precipitate consisting of the cyanides of gold and copper and chloride of silver is formed. This is well washed and boiled in aqua regia, which dissolves the gold and copper as chlorides, leaving the chloride of silver behind. The solution containing the gold and copper is evaporated nearly to dryness in order to remove the excess of acid, the residue is dissolved in a small quantity of water, and the gold precipitated therefrom as a brown metalic powder by the addition of sulphate of iron (copperas). The copper remains in solution. Finely divided zinc so-called zinc-dust is an excellent agent for the precipitation of gold in a pulverulent form from cyanide gilding baths. By adding zinc dust to an exhausted cyanide gilding bath, and throroughly shaking or stirring it from time to time, all the gold is precipitated in two or three days. The quantity of zinc required for precipitation depends of course on the quantity of gold present, but generally speak- ing* /^ lb. or at the utmost I Ib. of zinc-dust will be required for [OO quarts of exhausted gilding bath. ELECTRO-DEPOSITION OF METALS. The pulverulent gold obtained is washed, treated first with hydrochloric acid to remove adhering zinc -dust, and next with nitric acid to free it from silver and copper. From the acid mixtures serving for dead pickling gold, or for stripping, the gold is precipitated by solution of sulphate of iron (copperas) added in excess. The gold present is precipi- tated as a brown powder mixed with ferric oxide. This powder is filtered off and treated in a porcelain dish with hot hydrochloric acid, which dissolves the iron. The gold which remains behind is then filtered off, and, after washing, dissolved in aqua regia in order to work the solution into fulminating gold or neutral chloride of gold. CHAPTER XL DEPOSITION OF PLATINUM AND PALLADIUM, i DEPOSITION OF PLATINUM. Properties of platinum. Pure platinum is white with a grayish tinge ; it is as soft as copper, malleable, and very ductile. At a white heat it can be welded, but is fusible only with the oxyhy- drogen blowpipe or by the electric current. Its specific gravity is 21.4. Air has no oxidizing action upon platinum ; it is scarcely acted upon by any single acid ; prolonged boiling with con- centrated sulphuric acid appears to dissolve the metal slowly. The best solvent for it is aqua regia, which forms the tetrachlo- ride, PtCl 4 . Chlorine, bromine, sulphur, and phosphorus com- bine directly with platinum, and fusing saltpetre and caustic alkali attack it. Besides, in the malleable and fused state, platinum may be obtained as a very finely divided powder, the so -called platinum DEPOSITION OF PLATINUM AND PALLADIUM. 319 black, which is precipitated with zinc from dilute solution of platinum chloride acidulated with hydrochloric acid. Platinum baths. In view of the valuable properties of platinum of oxidizing only under certain difficult conditions, of possessing an agreeable white color, and of taking a fine polish, it seems strange that greater attention has not been paid to the electro-deposition of this metal than is actually the case. The reason for this may perhaps be found in the fact that the baths formerly employed for experiments pos- sessed many great defects, causing the operator many diffi- culties, and besides allowed only of the production of thin deposits. Giving due consideration to the requirements of the process of the electro-deposition of platinum and with the use of a suitable bath, deposits of platinum of a certain thickness can be readily produced, and necessary conditions will be de- scribed under "Treatment of platinum baths." The platinum baths formerly proposed did not yield quite satisfactory results, the content of platinum being too small in some of them, while with others dense deposits could not be obtained. A more recent formula by Boettger, however, gives a quite good bath. A moderately dilute solution of sodium citrate is added to platoso-ammonium chloride until an excess of the latter no longer dissolves, even after continued boiling. The following proportions have been found very suitable. Dis- solve 17^ ozs. of citric acid in 2 quarts of water, and neutral- ize with caustic soda. To the boiling solution add, with con- stant stirring, the platoso-ammonium chloride freshly precipi- tated from 2.64 ozs. of chloride of platinum, heat until solution is complete, allow to cool, and dilute with water to 5 quarts. To decrease the resistance of the bath, 0.7 or O.8 oz. of sal ammoniac may be added; a larger addition, however, will cause the separation of dark-colored platinum. The platoso-ammonium chloride is prepared by adding to a concentrated solution of chloride of platinum concentrated solution of sal ammoniac until a yellow precipitate is no longer formed on adding a further drop of sal ammoniac. The preci- 320 ELECTRO-DEPOSITION OF METALS. pitate is filtered off and brought into the boiling solution of sodium citrate. This bath works very uniformly if the content of platinum is from time to time replenished. " The Bright Platinum Plating Company," of London, has patented the following composition of a platinum bath: Chloride of platinum 0.98 oz., sodium phosphate 19^ ozs., ammonium phosphate 3.95 ozs., sodium chloride 0.98 oz., and borax 0.35 oz., are dissolved, with the aid of heat, in 6 to 8 quarts of water, and the solution is boiled for 10 hours, the water lost by evaporation being constantly replaced. The re- sults obtained with this bath were not much better than with Bottger's. Dr. W. H. Wahi gives the following directions for preparing platinum baths:* Alkaline platinate bath. Platinic hydrate 2 ozs., caustic potassa (or soda) 8 ozs., distilled water I gallon. Dissolve one-half of the caustic potassa in a quart of distilled water, add to this the platinic hydrate in small quanrity at a time, facilitating solution by stirring with a glass rod. When solution, is effected, stir in the other half of alkali dissolved in a quart of water ; then dilute with enough dfstilled water to form one gallon of solution. To hasten solution, the caustic alkali may be gently heated, but this is not necessary, as the platinic hydrate dissolves very freely. This solution should be worked with a current of about two volts, and will yield metal of an al- most silvery whiteness upon polished surfaces of copper and brass, and quite freely. There should be slight, if any, percep- tible evolution of hydrogen at the cathode, but a liberal evolu- tion of oxygen at the anode. An addition of a small proportion of acetic acid to this bath improves its operation where a heavy deposit is desired. The anode must be of platinum or carbon, and owing to the readiness with which the metal is deposited an excess of anode-surface is to be avoided. Articles of steel, nickel, tin, zinc, or German silver will be coated with black and * Journal of the Franklin Institute, July, 1890. DEPOSITION OF PLATINUM AND PALLADIUM. 321 more or less non-adherent platinum ; but by giving objects of these metals a preliminary thin electro-deposit of copper in the hot cyanide bath they may be electro-platinized in the alkaline platinate bath equally as well as copper. The bath may be worked hot or cold, but it is recommended to work it at a tem- perature not exceeding 100 F. It may be diluted to one-half the strength indicated in the formula and still yield excellent results. The surface of the objects should be highly polished by buffing or otherwise prior to their introduction into the bath, if the resulting deposit is designed to be brilliant. The deposition of platinum takes place promptly. In five minutes a sufficiently heavy coating will be obtained for most purposes. The deposited metal is so soft, however, that it re- quires to be buffed very lightly. A heavier deposit will appear gray in color, but will accept the characteristic lustre of platinum beneath the burnisher. An oxalate solution is prepared by dissolving i oz. of platinic hydrate in 4 ozs. of oxalic acid and diluting the solution to the volume of one gallon with distilled water. The solution should be kept acidified by the occasional addition of some oxalic acid. The simplest plan of using this bath, which requires no atten- tion to proportions, is simply to work with a saturated solution of the oxalate, keeping an undissolved excess always present at the bottom of the vessel. An addition of a small quantity of oxalic acid now and then will be found advantageous. The double salts of oxalic acid with platinum and the alkalies may be formed by saturatfng the binoxalate of the desired alkali with platinic hydrate and maintaining the bath in normal metallic strength by the presence of an undissolved residuum of platin- ous oxalate. The double oxalates are not so soluble in water as the simple salt. The oxalate baths, both of single and double salts, may be worked cold or hot (though not to exceed 150 F.) with a current of comparatively low pressure. The metal will deposit bright, reguline, and adherent on copper and brass. Other metallic objects must receive a preliminary coppering as above. 21 322 ELECTRO-DEPOSITION OF METALS. The deposited metal is dense, with a steely appearance, and can be obtained of any desired thickness. The deposit obtained in the oxalate bath is sensibly harder than that from the alkaline platinate bath, and will bear buffing tolerably well. The phosphate bath may be prepared by the following formula : Phosphoric acid, syrupy (specific gravity 1.7), 8 ozs., platinic hydrate I to I J^ ozs., distilled water I gallon. The acid should be moderately diluted with distilled water and the solution of the hydrate effected at the boiling tempera- ture. Water should be added cautiously from time to time to supply that lost by evaporation. When solution has taken place, the same should be diluted with sufficient water to make the volume I gallon. The solution may be worked cold or heated to 100 F., and with a current much stronger than that required for the platinates and oxalates. The ammonio (and sodio) platinic phosphates may be formed from the simple phosphate by carefully neutralizing the solution of the phos- phate with ammonia (or soda) ; then adding an excess of phosphoric acid, or enough to dissolve the precipitate formed, and an additional quantity to insure a moderate amount of free phosphoric acid in the bath. The phosphate baths will be maintained of normal strength by additions of platinic hydrate, the solutions of which will need to be assisted by heating the bath, preferably at the close of each day's work. The metal yielded by the electrolysis of these phosphate solutions is brilliant and adherent. It has the same steely appearance as that exhibited by the oxalate solutions, but to a less pro- nounced degree. The physical properties of the deposited metal are in other respects like those described in connection with that obtained from the oxalate baths. Management of platinum baths. Copper and brass may be directly coated with platinum, but iron, steel, and other metals have to be previously coppered ; without preliminary copper- ing these metals would soon decompose the platinum bath, DEPOSITION OF PLATINUM AND PALLADIUM. 323 independent of the fact that no perfect deposit of platinum can be produced upon them without the cementing intermediary layer of copper. Platinum baths must be used hot, and even then require a current of 5 to 6 volts. An abundant evolution of gas must appear on the objects and the anodes ; the anode-surface (platinum anodes) must not be too small, and should be only at a few centimetres distance from the objects. Since the platinum anodes do not dissolve, the content of platinum in the bath be- comes constantly smaller, and the bath must from time to time be strengthened. It is then heated in a porcelain dish or en- ameled vessel to the boiling-point, some fresh solution of sodium citrate is added, and platoso-ammonium chloride introduced as long as solution takes place. A concentrated solution of platoso-ammonium chloride may be kept at hand and a small quantity of it at intervals be added to the bath. Execution of platinizing, The objects thoroughly freed from grease and pickled, and, if necessary, coppered, are suspended in the bath heated to between 176 and 194 F. ; this tempera- ture must be kept up during the entire operation. The current should be of sufficient strength and the anodes placed so close to the objects that a liberal evolution of gas appears on the anodes. For platinizing large objects it is recommended to go round them, at a distance of 0.31 to 0.39 inch, with a hand- anode of platinum sheet, which should not be too small and should be connected to the anode-rod. When the current has vigorously acted for 8 to 10 minutes, the objects are taken from the bath, dried, and polished. However, for the production of heavy deposits for instance, upon points of lightning-rods the deposit is vigorously brushed with a steel-wire scratch-brush or fine pumice powder. The objects are then once more freed from grease and returned for 10 to 15 minutes longer to the bath to receive a further deposit of platinum with a weaker cur- rent, which must, however, be strong enough to cause the escape of an abundance of gas-bubbles. The objects are then taken out, and, after immersion in hot water, dried in sawdust. 324 ELECTRO-DEPOSITION OF METALS. The deposit is then well burnished, first with the steel tool, and finally with the stone, whereby the gray tone disappears and the deposit shows the color and lustre of massive platinum sheet. Points of lightning-rods platinized in this manner were without flaw after an exposure to atmospheric influences for more than six years. Platinizing of glass. Glass may be platinized by means of the galvanic current as follows : Dissolve 14 drachms of platinic hydrate in 17^ ozs. of a 10 per cent, solution of caustic soda or potash. Add to the solution 17^ ozs. more of the alkali solution and dilute with water to 2 quarts. The temperature of the bath should not exceed 100 F., and the strength of the current should be two volts. Platinizing by contact. Though a thick deposit cannot be produced by the contact-process, Fehling's directions may here be mentioned as suitable for giving a thin coat of platinum to fancy articles. He recommends a solution of 5.64 drachms of chloride of platinum and 7 ozs. of common salt in I quart of water, which is made alkaline by the addition of a small quantity of soda lye, and for use heated to the boiling point. If larger articles are to be platinized by contact, free them from grease, and after pickling, and if necessary, coppering, wrap them round with zinc wire or place them upon a bright zinc sheet and introduce them into the heated bath. All the remaining manipulations are the same as in other contact pro- cesses. Recovery of platinum from platinum solutions. From not too large baths, precipitation of the platinum with sulphuretted hydrogen is the most suitable method, and preferable to evapo- rating and reducing the metal from the residue. The process is as follows: Acidulate the platinum solution with hydrochloric acid, and, after warming it, conduct sulphuretted hydrogen into it. The metal (together with any copper present) precipitates as sulphide of platinum. The precipitate is filtered off, dried, .and glowed in the air, whereby metallic platinum remains be- hind. From larger baths the platiuum may be precipitated by DEPOSITION OF PLATINUM AND PALLADIUM. 325 suspending bright sheets of iron in the acidulated bath. In both cases the precipitated platinum is treated with dilute nitric acid in otder to dissolve any copper present. After filtering off and washing the pure platinum, dissolve it in aqua regia; the solution is then evaporated to dryness in the water bath, and the chloride of platinum thus obtained may be used in making a new bath. 2. Deposition of Palladium. Properties of palladium. Palladium, when compact, has a white color and possesses a lustre almost equal to that of silver. Its specific gravity is about 1 2.0; it is malleable and ductile, and may be fused at a white heat. In the oxyhydrogen flame it is volatilized, forming a green vapor. It is less permanent in the air than platinum. It is dissolved by nitric acid ; it is scarcely attacked, however, by hydrochloric or sulphuric acid. Hydriodic acid and free iodine coat it with the black palladium iodide. On account of the high price of its salts, palladium has been but little used for electro-plating purposes ; nor for the same reason, is it likely to be more extensively employed in the future. According to M. Bertrand, the most suitable bath consists of a neutral solution of the double chloride of palladium and ammonium, which is readily decomposed by 3 Bunsen ele- ments coupled one behind the other (therefore about 5.4 volts). A sheet of palladium is used as anode. A solution of palladium cyanide in potassium cyanide does not yield as good results as the above bath. Palladium possessing the property of not being blackened by sulphuretted hydrogen, it is for this reason frequently used for coating silver-plated metallic articles with a thin deposit of it. Palladium has also of recent years been employed for plat- ing watch movements. According to M. Pilet, 4 milligrammes (about T y grain) of palladium is sufficient to coat the works of an ordinary sized watch. M. Pilet recommends the following 326 ELECTRO-DEPOSITION OF METALS. bath: Water 2 quarts, chloride of palladium 5^ drachms, phosphate of ammonia 3^ ozs., phosphate of soda 17^ ozs., benzoic acid 2^ drachms. Deposits of iridium and rhodium have recently been produced from baths similar in composition to those mentioned under palladium. But as these metals would be used for plating pur- poses only in isolated cases, it is not necessary to enter into details. CHAPTER XII. DEPOSITION OF TIN, ZINC, LEAD, AND IRON. i. Deposition of Tin. Properties of tin. Tin is a white, highly lustrous metal ; it possesses but little tenacity, but has a high degree of malleabil- ity, and tin-foil may be obtained in leaves less than sVth of a milli-metre in thickness. Tin melts at about ^46 F. and evap- orates at a high temperature ; the fused metal shows great tendency to crystallize on congealing. By treating the surface of melted tin with a dilute acid, the crystalline structure ap- pears as designs (moire metallique), resembling the ice-flowers on frosted windows. Tin remains quite constant even in moist air, and resists the influence of an atmosphere containing sulphuretted hydrogen. Strong hydrochloric acid quickly dissolves tin on heating, evolv- ing hydrogen and forming stannous chloride. Dilute sulphuric acid has but little action on the metal ; when heated with con- centrated sulphuric acid, sulphur dioxide is evolved. Dilute nitric acid dissolves tin in the cold without evolution of gas ; concentrated nitric acid acts vigorously upon the metal, whereby oxide of tin, which is insoluble in the acid, is formed. Alkaline lyes dissolve the metal to sodium stannate, hydrogen being thereby evolved. DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 327 Tin baths. The bath used by Roseleur for tinning with the battery works very well. It is composed as follows : I. Pyrophosphate of soda 3.5 ozs., tin-salt (fused) 0.35 oz., water 10 quarts. To prepare the bath dissolve the pyrophos- phate of soda in 10 quarts of rain water, suspend the tin-salt in a small linen bag in the solution, and move the bag to and fro until its contents are entirely dissolved. Objects of zinc, copper, and brass are directly tinned in this bath with a current of slight tension. Articles of iron and steel are first coppered or preliminarily tinned in a bath prepared according to formula VIII., (see p. 33 I ) the deposit of tin being then aug- mented in bath I. with the battery current. Cast-tin anodes as large as possible are used, which, however, will not keep the con- tent of tin in the bath constant. It is therefore necessary, from time to time, to add tin-salt, which is best done by preparing a solution of 3.5 ozs. of pyrophosphate of soda in I quart of water and introducing into the solution tin salt as long as the latter dissolves clear. Of this tin essence add to the bath more or less, as may be required, and also augment the content of pyro- phosphate of soda, if, notwithstanding the addition of tin-salt, the deposition of tin proceeds sluggishly. Though the bath composed according to formula I. suffices for most purposes, an alkaline tin bath, first proposed by Eisner and later recommended by Maistrasse, Fearn, Birgham, and others, with or without addition of potassium cyanide, may be mentioned as follows: II. Crystallized tin-salt 0.7 oz., water I quart, and potash lye of 10 Beaume until the precipitate formed dissolves. As seen from the formula the solution of tin-salt is com- pounded with potash lye of the stated concentration (or with a solution of i oz. of pure caustic potash in water), until the pre- cipitate of stannous hydrate again dissolves. Some operators recommend the addition of 0.35 oz. of potas- sium cyanide to the solution. Without potassium cyanide the bath requires 3.75 to 4 volts, and with it, 3.5 volts. 328 ELECTRO-DEPOSITION OF METALS. In testing Salzede's bronze bath (p. 247), it was found to yield quite a good deposit of tin directly upon cast-iron, and it was successfully used for this purpose by omitting the cuprous chloride and using 14.11 drachms of stannous chloride, so that the composition became as follows : Ha. 98 per cent, potassium cyanide 3.5 ozs., carbonate of potassium 35j{ ozs., stannous chloride 14.11 drachms, water 10 quarts. With 4 volts a heavy deposit was rapidly obtained. III. A tin bath of stannous chloride, caustic soda, and potas- sium cyanide, given by Pfanhauser, contains 1 1 % drachms of stannous chloride, equal to about 7^ drachms of metallic tin per quart. It is still more advantageous to use double the quantity of tin, the composition of the bath being then as follows : Water 10 quarts, fused stannous chloride 14 ozs., caustic soda 17^? ozs., 100 per cent, potassium cyanide 3^ ozs. The bath, as above composed, contains about 15 drachms of metallic tin per quart, and with 3^ volts furnishes a deposit of tin of about 4^ grains per hour. Pfanhauser has made new experiments and found that still more favorable results are obtained with a solution of I ^ ozs. of stanno-ammonium chloride in I quart of water, a deposit of 9^> grains of tin per hour being obtained with a current of only \y 2 volts. The solution of the salt is readily effected. Cast-tin anodes are to be used. The temperature of the bath should be between 68 and 77 F. In case the bath becomes poor in metal, stanno-ammonium chloride is added. The deposit of tin is rather rough, but can be readily made bright by treatment with brass scratch-brushes. IV. A tin bath given by Taucher is composed as follows : Water 500 quarts, sodium or pyrophosphate 1 1 Ibs., crystallized tin-salt 21 ozs., or, still better, fused tin-salt 17^ ozs. Bring the water into a tank completely lined with plates or anodes of tin joined together and connected with the positive DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 329 pole wire. Dissolve the pyrophosphate in the water, stirring constantly. Place the tin-salt in a copper-sieve, and immerse the latter about one-half in the solution ; an abundant milky turbidity is immediately formed, which, however, disappears on stirring. When all the tin-salt is dissolved, remove the sieve, and the tin-bath, which now forms a clear fluid, either colorless or of a slightly yellowish color, is ready for use, it being only necessary to secure the articles to be tinned to the rods con- nected with the negative pole. The anodes do not suffice to keep the bath saturated, and hence, when the deposit becomes weaker, small quantities of equal parts of tin-salt and of sodium pyrophosphate have to be added. The solution of these salts should always be effected with the assistance of a sieve to prevent small pieces of tin-salt from falling to the bottom of the bath, where they would be enveloped by an almost insoluble crust and remain nearly unchanged. This tin bath is suitable for all kinds of metals, the deposit obtained combining with considerable solidity a matted and white appearance closely resembling silver. Management of tin baths. Tin baths should not be used at a temperature below 68 F. ; they require (formulae I. and II.),. according to their composition, a current of 2 to 3 volts, so that two Bunsen elements coupled one after the other suffice for all purposes. Too strong a current causes a pulverulent reduction of the tin, which does not adhere well, while with a suitable current-strength quite a dense and reguline deposit is obtained. Cast-tin plates with as large a surface as possible are used as anodes. The choice of the tin-salt exerts some influence upon the color of the tinning. By using, for instance, crystallized tin- salt, which is always acid, in preparing the bath according to formula I., a beautiful white tinning with a bluish tinge is ob- tained, which, however, does not adhere so well as that pro- duced with fused tin- salt. Again, the latter yields a somewhat .dull gray layer of tin, and, therefore, the effects of the bath will have to be corrected by the addition of one or the other salt. 33 ELECTRO-DEPOSITION OF METALS. As previously mentioned, iron and steel objects are best sub- jected to a light preliminary tinning by boiling in the bath VIII. (see p. 331 ) ; however, instead of this preliminary tinning, they may first be electro-coppered and, after scratch-brushing the copper deposit, brought into the tin bath. When the action of the bath becomes sluggish, it has to be refreshed (for formula I.) by the addition of tin salt and pyro- phosphate of soda, or (for formula II.) by the addition of potash lye and tin-salt. Process of tinning. From what has been said, it will be evi- dent that the execution of tinning is simple enough. After being freed from grease and pickled, the objects are brought into the bath and tinned with a weak current. For heavy de- posits of tin the objects are frequently taken from the bath and the deposit is thoroughly brushed with a brass scratch-brush, not too hard, and moistened with dilute sulphuric acid (i part acid of 66 Be. to 25 water) when, after rinsing in water, the articles are returned to the bath. If, with the use of too strong a current, the color of the deposit is observed to turn a dark dull gray, scratch-brushing must be repeated. When the tin- ning is finished the articles are brushed with a brass scratch- brush and decoction of soap-root, then dried in sawdust and polished with fine whiting. Tinning by contact and boiling. For tinning by zinc contact in the boiling tin bath the following solutions may be recom- mended : V. According to Gerhold : Pulverized tartar and alum, of each 3.5 ozs., fused stannous chloride 14 drachms, rain-water 10 quarts. VI. According to Roseleur: Potassium pyrophosphate /ozs., crystallized stannous chloride (tin-salt), n drachms, fused Stan- nous chloride 2.8 ozs., rain-water 10 quarts. VII. According to Roseleur, for tinning by immersion : Potas- sium pyrophosphate 5.6 ozs., fused stannous chloride 1.23 ozs., rain-water 10 quarts. Formulae V. and VI. yield good results. For tinning by con- DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 331 tact, 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 de- posit requires, of course, a longer time. By using the electric current the deposit can be made as heavy as desired. By im- mersion in the bath prepared according to formula VII., zinc can only be coated with a very thin film of tin, which, however, by the use of a battery, can be made as heavy as desired. For tinning by contact in a cold bath, Zilken has patented the following solution: Dissolve with the aid of heat in 100 quarts of water, tin-salt 7 to 10.5 ozs., pulverized alum 10.5 ozs., common salt 15^ ozs., 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 pro- cess 8 to 10 hours. Tinning solution for iron and steel articles. VIII. Crystal- lized ammonium-alum 7 ozs., crystallized stannous chloride 2.8 drachms, fused stannous chloride 2.8 drachms, rain-water 10 quarts Dissolve the ammonium-alum in the hot water, and when dissolved add the tin-salts. The bath is to be used boil- ing hot and kept at its original strength by an occasional addi- tion of tin-salt. The clean and pickled iron objects, 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 sawdust in the tumbling drum. Tinning by boiling in this bath is the most suitable preparation for iron and steel objects, which are to be provided with a heavy electro-deposit of tin. To be en- tirely sure of success it is recommended thoroughly to scratch- brush the objects, then to return them once more to the bath, and finally to suspend them in a bath composed according to formula I. or II. A tinning solution for small brass and copper articles (pins, 332 ELECTRO-DEPOSITION OF METALS. 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 sieve or in contact with pieces of zinc ; frequent stirring with a tin rod shortens the process. Another solution, given by BSttger, also yields good results : Dissolve oxide of tin by boiling with potash lye, and place the copper or brass objects to be tinned in the boiling solution in contact with tin shavings. Eisner s bath yields equally good results. It consists of a solution of equal parts of tin-salt and common salt in rain- water. The manipulation is the same as given above. A durable coating of tin is also produced with the use of potassium stannate, which is prepared as follows : Tin is melted and then granulated by pouring it into water. The granulated tin is brought into a vessel of glass or porcelain and crude nitric acid poured over it, whereby, with strong effervescence of the fluid and the evolution of brown-red vapors, it is converted into a white powder consisting of stannic oxide. The latter is sep- arated from the unchanged tin by washing with water, and dried. The dry powder is mixed with pure potash in the pro- portion of 3 parts stannic oxide and 4 parts potash. The mixture is melted in an iron crucible and the fused mass poured upon a stone slab. It consists of potassium stannate and is dissolved in boiling water. Potassium stannate may also be prepared by adding to a solution of tin-salt in water aqua am- monia as long as a precipitate is formed. The mass is then allowed to drain off upon a linen cloth and repeatedly washed with water. The residue, consisting of stannous hydrate, is boiled with strong potash lye, and the solution of potassium stannate thus obtained diluted with water. The tinning of needles is effected by spreading them out upon a sieve and immersing the latter in the bath ; larger articles are touched with a tin-rod while in the bath. The temperature of the bath should be between 122 and 212 F. Larger articles DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 333 of brass or bronze are best coppered previous to tinning, which is effected by wrapping them with iron wire and immersing them in dilute sulphuric acid for a short time ; hydrochloric acid may be substituted for the sulphuric acid. Tinning may also be effected by dissolving I part tin-salt in 10 parts water, adding to the solution one of 2 parts of caustic potash in 20 of water and stirring until the fluid is clear. The articles to be tinned are placed upon a tin plate. The latter is brought into the hot bath and touched on several places with tin rods. To give articles of brass, copper, or iron a thin, superficial coating of tin, dip them in a solution of tin-salt in which granu- lated tin has been lying for some time, then dust them with tin- powder, rub them with a woollen rag, and repeat the operation until the article appears tinned. 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 solu- tion a small sponge and dip the latter into pulverulent zinc. By then rubbing the thoroughly-cleansed and pickled articles with the sponge they imediately become coated with a film of tin. To obtain uniform tinning, the sponge must be repeatedly dipped now into the solution and then into the zinc-powder, and the rubbing continued for a few minutes. For coloring and platinizing tin, see special chapter. 2. Deposition of Zinc. Properties of zinc. Zinc is a bluish-white metal, possessing high metallic lustre. It melts at 776 F. At the ordinary temperature zinc is brittle, but it is malleable at between 212 and 300 F., and can be rolled into sheets; at 392 F. it again becomes brittle and may be readily reduced to powder. The specific gravity of zinc varies from about 6.86 to 7.2. When strongly heated in the air or in oxygen it burns with a greenish- white flame, producing dense white fumes of the oxide. In moist air it becomes coated with a thin layer of basic car- 334 ELECTRO- DEPOSITION OF METALS. bonate, which protects the metal beneath from further oxida- tion. Pure zinc dissolves slowly in the ordinary mineral acids, but the commercial article containing foreign metals is rapidly attacked, with evolution of hydrogen. Zinc being a very electro-positive metal, precipitates most of the heavy metals from their solutions, especially copper, silver, lead, antimony, arsenic, tin, cadmium, etc., this being the reason why in dissolving impure zinc the admixed metals do not pass into solution so long as zinc in excess is present. Caustic alkalies also dissolve zinc with formation of an oxide and free hydrogen, especially when it is in contact with a more electro- negative metal. Zinc in contact with iron protects the latter from rust, and also prevents copper from dissolving when in contact with it. Zinc baths. Although most metals can be readily plated with a thin, firmly-adhering layer of zinc, experiments to pro- duce in an easy and convenient manner, upon shaped articles, really uniform thick deposits which would answer all require- ments, particularly the prevention of the oxidation of iron, have not been entirely successful. The zinc deposits first upon the projecting edges and portions of the objects, while the por- tions at a greater distance from the anodes are either not coated at all or only with a very thin film, no matter whether the zinc bath is prepared so as to conduct readily or not readily. In electro-zincking smooth sheet iron this drawback does not make itself felt, but, on the other hand, the fact that with the most suitable current-strength for a normal and homogeneous deposit the latter is formed too slowly, is an obstacle to the substitution of electro-zincking for the ordinary process of gal- vanizing. Numerous exhaustive experiments have been made to produce in a practicable manner and in a short time a zinc- deposit of sufficient thickness upon iron, and while some of these experiments were successful in so far that zinc deposits were produced which, as regards thickness and density, were not only equal, but superior to those by the ordinary galvaniz- ing method, the cost considerably exceeded that of the latter process. DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 335 Better results are obtained in zincking articles with depres- sions by depositing not pure zinc but zinc in combination with other metals. In doing this, of course, zinc must be present largely in excess if the deposit is to have the effect of pure zinc in protecting the plated article from rust. By the addi- tion of salts of magnesium and aluminium to the zinc bath, Schaag and others have endeavored to deposit zinc with a con- tent of these metals. While the possibility of depositing alu- minium from aqueous solutions is doubtful, it is very likely that in Schaag's patented process neither the magnesium nor the aluminium is the effective agent, but the tin or mercury, salts of which, Schaag also adds to the zinc bath. But such additions are nothing new, since deposits of zinc-tin alloys with and without mercury salts have for many years been produced. The same effect is produced by an addition of tin and nickel to the zinc bath, and experiments have conclusively shown that deposits upon iron produced in such a bath protect the iron from rust as well as a deposit of pure zinc. Below the pure zinc baths mostly used are given : I. Sulphate of zinc (white vitriol) 2.8 ozs., ammonium sul- phate I y^ ozs., sal ammoniac 1 1 drachms, water I quart. Dis- solve the salts in the heated water and use the bath at 68 F. The current-strength should only be slightly greater than nec- essary for the decomposition of the bath ; the current of two Bunsen elements coupled one after the other is quite too strong, and must, therefore, be correspondingly weakened by the resistance-board. As anodes, rolled zinc sheets of not too small dimensions are to be used. This bath is suitable for heavily zincking objects (sheets and plates) of wrought- and cast-iron, steel, and all other metals, but not for zincking hollow articles if anodes can- not at equal distances be placed around them. The most suit- able tension is 2.8 to 3 volts. II. Caustic potash 2 ozs., chloride of zinc 5*^ drachms, sal ammoniac II drachms, water I quart. Dissolve the caustic potash in one-half of the water, and the chloride of zinc and ELECTRO-DEPOSITION OF METALS. sal ammoniac in the other half, and mix the solution with stirring. The result is a clear fluid which requires a current of 2.5 to 3 volts for its decomposition. Zinc sheets are also used as anodes. In this bath the deposit upon hollow objects pro- ceeds better than in the preceding, though frequent turning of the articles is necessary. III. Alum 3^ ozs., hydrated oxide of zinc 5^ drachms, water I quart. Dissolve 14 drachms of sulphate of zinc in i pint of water, and carefully add potash lye until a further drop of it no longer produces a precipitate. Since potash lye dis- solves the hydrated oxide of zinc, an excess has to be avoided. The precipitate is filtered off, washed with water, and the hy- drated oxide of zinc, while still moist, is heated together with the solution of 3^ ozs. of alum in I quart of water, whereby it is completely dissolved. This bath requires a current of 3 to 3.5 volts. IV. Sulphate of zinc (white vitriol) 2.8 ozs., water I quart, and potash lye sufficient to redissolve the precipitated hydrated oxide of tin. This bath also works quite well, and requires from 2.75 to 3 volts and 1.5 amperes per 15 j square inches. Solution of cyanide of zinc in potassium cyanide may also be used for zincking, such a bath having been warmly recom- mended by some authors. However, the production of deposits of some thickness requires a long time, and the deposit itself shows a tendency to peel off. Execution of zincking. Next to thorough cleansing and pickling the objects, especially iron castings, and regulating the current, electro-zincking depends on the frequent turning and changing of the objects in the bath, since the deposit is chiefly formed upon the portions nearest to the anodes T and not at all, or with difficulty, upon the portions away from the anodes. If, notwithstanding frequent changing, some portions do not acquire a deposit, recourse must be had, as in nickeling, to the hand anode. Next to frequently changing the articles in the bath, it is recommended to scratch-brush them several times, especially if heavy deposits are to be produced. It is also advisable to somewhat heat the baths, if possible. DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 337 It is of advantage to superficially zinc iron objects by a com- bined process of contact and boiling, and then to augment the layer of zinc in the bath. After thorough scratch-brushing with a steel brush, not too hard, and a decoction of soap-root, the zincked objects are rinsed in lime-water, then plunged into hot water, and dried in saw-dust ; polishing is effected upon soft cloth bobs with Vienna lime and oil. For zincking iron by contact quite a concentrated solution of chloride of zinc and sal ammoniac in water, only, is suitable, in which the objects are placed in contact with large surfaces of zinc. To coat brass and copper with a bright layer of zinc proceed as follows : Boil commercial zinc-gray, i. e., very finely-divided metallic zinc, several hours with concentrated solution of caus- tic soda. Then immerse the articles to be zincked in the boil- ing fluid, when, by continued boiling, the articles 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. Weil zincks copper and coppered objects by immersing them in a boiling concentrated solution of caustic potash in contact with zinc. The coating thus obtained is said to be adherent and brilliant. For coloring and platinizing zinc, see special chapter. Zinc alloys. The production of the principal zinc alloy, brass, by the galvanic method, having already been mentioned, and also that of a zinc-nickel-copper alloy (German silver), it remains to give an alloy of zinc with tin, or of zinc, tin and nickel, which can be produced by the use of the battery. A suitable bath for depositing this alloy consists of: Chloride of zinc 6^ drachms, crystallized stannous chloride 9 drachms, pulverized tartar 9 drachms, pyrophosphate of soda 2 ^ drachms, water I quart. Dissolve the salt at a boiling heat, and filter the cold solution, when it is ready for use. For anodes, cast plates of equal parts of tin and zinc are used. 22 33 8 ELECTRO-DEPOSITION OF METALS. These deposits have no special advantages, but, on the other hand, a deposit containing zinc in large excess has the same ef- fect of protecting iron from rust as a deposit of pure zinc. By preparing a bath which contains as conducting salt sodium citrate, and ammonium chloride, and the chlorides of the metals in the proportion of 4 zinc chloride to I tin chloride, a deposit is obtained which not only is a perfect protection against rust, but also enters far better into depressions than pure zinc. By adding to the bath a small quantity of chloride of mercury or of nickel, alloys of zinc, tin and mercury or of zinc, tin and nickel are formed which are distinguished from pure zinc deposits by a finer structure. 3. Deposition of Lead. The properties of lead only interest us in so far as it being less attacked by most mineral acids than other metals, objects have been coated with it in order to protect them against the action of such agents. For decorative purposes electro- deposits of lead are not used, and those as a protection against chemical influences cannot be produced of sufficient thickness for that purpose. Lead baths. I. Dissolve, by continued boiling, caustic potash 1.75 ozs. and finely pulverized litharge 0.17 oz. in I quart of water. II. According to Watt, the following solution is used : Acetate of lead 0.17 oz., acetic acid 0.17 oz., water I quart. The bath prepared according to formula I. deserves the preference. Lead baths require anodes of sheet- lead or cast-lead plates, a very weak current, and in order to produce a dense deposit of some thickness, the objects have to be frequently scratch- brushed. Iron is best previously coppered. Superoxide of lead being separated upon the anodes, they have to be fre- quently cleansed with a scratch-brush. The formation of superoxide of lead is utilized for the production of the so- called Nobili's rings (electrochromy), which will be mentioned below. DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 339 To coat gun barrels and other articles of steel or iron with superoxide of lead as a protection against rust, suspend the bright articles as anodes in a solution of nitrate of lead mixed with ammonium nitrate. Leading by contact is effected by suspending the objects, previously thoroughly freed from grease, in the boiling solution prepared according to formula L, in contact with a piece of tin. Metallic chromes (Nobili's rings, iridescent colors, electro- chromy.) The separation of superoxide of lead upon the anodes or upon objects suspended as anodes, produces superb effects of colors. For the production of such colors, a bath is prepared by boiling for half an hour 3 J^ ozs. of caustic potash, 14 drachms of litharge, and I quart of water. The operation is as follows : Suspend the articles, carefully freed from grease and pickled, to the anode-rods, and with a weak current intro- duce in the lead solution a thin platinum wire connected with the object-rod by flexible copper wire, without, however, touch- ing the article. The latter will successively become colored with various shades yellow, green, red, violet, and blue. By the continued action of the current, these colors pass into a discolored brown, which also appears in the beginning if the current is too strong, or the platinum wire be immersed too deep. Such unsuccessful coloration has to be removed by rapidly dipping in aqua fortis, and, after rinsing in water, sus- pending the article in the bath. For coloring not too large surfaces, a medium-sized Bunsen element is, as a rule, sufficient, if the platinum wire be immersed about ^ inch. Colors of all possible beautiful contrasts may be obtained by perpendicularly placing between the objects to be colored and the platinum wire a piece of stout parchment paper, or pro- viding the latter with many holes or radial segments. Another process of producing these effects of colors is as follows: Prepare a concentrated solution of acetate of lead (sugar of lead), and after being filtered, pour it into a shallow porcelain dish. Then immerse a plate of polished steel in the 340 ELECTRO-DEPOSITION OF METALS. solution, and allow it to rest upon the bottom of the dish. Now connect a small disc of sheet copper with the wire proceed- ing from the zinc element of a constant battery of two or three cells, the wire connected with the copper element being placed in contact with the steel plate. If now the copper disc be brought as close to the steel plate as possible without touching it, in a few moments a series of beautiful prismatic colorations will appear upon the steel surface, when the plate should be removed and rinsed in clean water. These colorations are films of lead in the state of peroxide, and the varied hues are due to the difference in thickness of the precipitated peroxide of lead, the light being reflected through them from the pol- ished metallic surface beneath. By reflected light every pris- matic color is visible, and by transmitted light a series of pris- matic colors complementary to the first colors will appear occupying the place of the former series. The colors are seen to the greatest perfection by placing the plate before a window with the back to the light, and holding a piece of white paper at such an angle as to be reflected upon its surface. The colorations are not of a fugitive character, but will bear a con- siderable amount of friction without being removed. In proof of the lead oxide being deposited in films or layers, it may be stated that if the deposit be allowed to proceed a few seconds beyond the time when its greatest beauties are exhibited, the coloration will be less marked, and become more or less red, green or brown. If well rubbed, when dry, with the finger or fleshy part of the hand, a rich blue colored film will be laid bare by the removal of the delicate film above it. The plan recommended by Mr. Gassiot to obtain the metallo- chrdmes is to place over the steel plate a piece of card cut into some regular device, and over this a rim of wood, the copper disc being placed above this. Very beautiful effects are obtained when a piece of fine copper wire is turned up in the form of a ring, star, cross or other pattern, and connected with the positive electrode, this being in fact one of the simplest and readiest methods of obtaining the colorations upon the DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 341 polished metal. Metallo-chromy is extensively employed in Nuremberg to ornament metallic toys. It has been adopted in France for coloring bells, and in Switzerland for coloring the hands and dials of watches. In using the lead solutions to produce metallic chromes, it must be remembered that me- tallic lead becomes deposited upon the cathode, consequently the solutions in time become exhausted, and must therefore be renewed by the addition of the lead salt. 4. Deposition of Iron (Steeling). The principal practical use of the electro-deposition of iron is to cover printing plates of softer metals with a coating of " steel," to increase their wearing qualities. The steeling of printing plates, however, has no advantage over nickeling or cobalting, which has been introduced with the best success. Steel baths. I. According to Varrentrapp : Pure green vitriol 43^ ozs., sal ammoniac 3^ ozs., water I quart. Boil the water for */ 2 hour to remove all air, and, after cooling, add the green vitriol and sal ammoniac. By the action of the air, and the oxygen appearing on the anodes, this bath is readily decomposed, insoluble basic sulphate of iron being separated as a delicate powder, which has to be frequently removed from the fluid by filtering. To decrease decomposition, the double sulphate of iron and ammonium, which can be more readily obtained pure and free from oxide, may be used. II. Sal ammoniac 3^ ozs., water I quart. This neutral solution of sal ammoniac may be made into an iron bath by hanging in it iron sheets as anodes, suspending an iron or copper plate as cathode, and allowing the current to circulate until a regular separation of iron is attained, which is generally the case in 5 to 6 hours. Although a separation of hydrated oxide of iron also takes place in this bath, it is in a less degree than in that prepared according to formula I. For the pro- duction of not too heavy a deposit of iron, some operators claim to have obtained the best results with this bath. According to Boettger the following bath serves for steeling : 342 ELECTRO-DEPOSITION OF METALS. III. Potassium ferrocyanide (yellow prussiate of potash) 0.35 oz., Rochelle salt 0.7 oz., distilled water 200 cubic centi- meters. To this solution is added a solution of 1.69 drachms of persulphate of iron in 50 cubic centimeters of water, whereby a moderate separation of Berlin blue takes place. Then add, drop by drop, with constant stirring, solution of caustic soda until the blue precipitate has disappeared. The clear slightly yellow- ish solution thus obtained can be directly used for steeling. This bath is considered excellent for coating engraved copper- plates with iron. For the production of electrotypes in iron the following baths (IV. and V.) are most suitable: IV. Ammonio-ferrous sulphate I ^ ozs., water I quart. The solution must be kept absolutely neutral, which according to Klein's suggestion is, on the one hand, to be attained by the use of large anode-surfaces, and, on the other, by suspending in the bath a copper plate and connecting it with the anodes. It would seem more advantageous to maintain the neutrality of the bath by suspending in it small bags filled with carbonate of magnesia. V. This steel bath highly recommended by Klein consists of a solution of equal parts of green vitriol and sulphate of mag- nesia, which is kept neutral by bags filled with carbonate of magnesia suspended in the fluid. The most suitable concentra- tion of the solution corresponds to a specific gravity of 1.55 ; and according to the most recent experiments, the current- density should at the utmost amount to 0.02 ampere per 15 j square inches, with a distance of I */ 2 inches of the anodes from the plate, this distance to be gradually increased. For steeling his copper printing plates, which are frequently of quite large dimensions, C. Obernetter, of Munich, employs the following method: The plate to be steeled is first freed from all color, which is best effected by means of chloroform or oil of turpentine. It is then thoroughly washed and brushed by means of a bristle-brush with potash lye or a solution of I part potassium cyanide in 20 parts water, and again washed. DEPOSITION OF TIN, ZINC, LEAD, AND IRON. 343 In this state the plate is suspended to the cathode of the steel- ing bath. A clean steel plate serves as anode. Both the anode and cathode are in a horizontal position. Bubbles form- ing on the cathode are readily removed by means of a feather. In about five minutes the plate is thoroughly steeled. The iron bath consists, according to Obernetter, of ferrous sulphate 30 parts by weight, iron-alum 30, sal ammoniac 60, dissolved in warm distilled water 1000. The solution is allowed to stand for two days, and is then filtered twice. It should also be filtered every time before use. After steeling, the plate is cleansed in the above described manner, and oiled to prevent rusting. When during the operation of printing the deep places of the plate commence to become red, i. e., when the copper shines through, the steeled plate may be re-steeled, but, according to Obernetter, this should not be done more than once. It is best in every case to first remove the old steeling with dilute sul- phuric or nitric acid, and then to re-steel the plate. According to Obernetter's statements, 21,000 copies were printed from a plate thus steeled without the plate suffering any injury, the last impression being in every respect equal to the first. For decorative purposes, a deep black deposit of iron may, according to u La Melallurgie," be produced as follows: Dis- solve as large a quantity of steel filings as possible in 50 quarts of commercial hydrochloric acid. The saturation of the solu- tion is recognized by a sediment, which no longer dissolves, being formed on the bottom of the vessel. Then add 2 Ibs. of white arsenic, and vigorously stir the mixture. The arsenic dissolves very slowly, but the bath cannot be considered fin- ished until all of it is dissolved, and the color obtained by means of the bath is the deeper the more complete the solution of the arsenic. The articles to be treated are connected to the nega- tive pole of the battery, iron and carbon plates serving as anodes. For a bath of 50 quarts, two Bunsen elements about 7^4 inches high are required, and the bath being very acid, the 344 ELECTRO-DEPOSITION OF METALS. articles must be connected with the battery prior to immersion. Upon copper and brass the deposit is directly produced, but iron articles being attacked by the bath, are first provided with a coat of nickel. The deposit of iron upon this nickel coating is very beautiful, and has been designated as " black nickel- ling." The coating must, of course, be protected from oxida- tion by a colorless lacquer. Management of iron baths. As previously mentioned, the insoluble precipitate from time to time formed in the bath has to be removed by filtration. This precipitate is, however, very delicate, 'and when stirred up might settle upon the ob- jects and prevent the adherence of the deposit. It is, therefore, advisable to use for steel baths, vats of much greater depth than correspond to the height of the objects, whereby the stirring up of the sediment in suspending the objects in the bath is best avoided. The baths must be kept thoroughly neutral, which may be effected in various ways. One method has already been mentioned in connection with formula IV. ; another method, which has been used with decided success, consists in precipitating, excluding the air as much as possible, a solution of pure green vitriol with ammonium carbonate, quickly filtering off the ferrous carbonate, washing the latter once or twice in cold water previously boiled, stirring it while moist into the bath, and allowing it to settle for one hour. Execution of steeling. Only the manipulations for the pro- duction of thin deposits will here be discussed. The production of heavy galvanoplastic deposits of iron will be explained later on under " Galvanoplasty." The clean and pickled objects are coated in the baths ac- cording to formulae I. and II. with a current of I to 1.25 volts, and the anodes at a distance of 3^ to 4^ inches, after which the current is reduced to 0.75 or i volt. To produce iron de- posits of any kind of thickness, the escape of the hydrogen bubbles which settle on the objects must be promoted by frequent blows with the finger upon the object-rod. As anodes, iron sheets of a large surface freed from scale by pickling are DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 345 to be used. When steeling is finished, the articles are thor- oughly rinsed, then plunged into very hot water, and, after drying in sawdust, placed for several hours in a drying cham- ber heated to about 212 F., to expel all moisture from the pores. Steeling by contact is readily effected by touching the objects with zinc, best in a bath prepared according to formula I. CHAPTER XIII. DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. I. Deposition of Antimony. Properties of Antimony. Electro- deposited antimony pos- sesses a gray lustre, while native, fused antimony shows a silver-white color. Antimony is hard, very brittle, and may easily be reduced to powder in a mortar. It melts at 842 F., and at a strong red heat takes fire and burns with a white flame, forming the trioxide. Its density is 6.8. It is permanent in the air at ordinary temperatures. Cold, dilute, and concentrated sulphuric acid have no effect upon antimony, but the hot con- centrated acid forms sulphide of antimony. By nitric acid the metal is more or less energetically oxidized, according to the strength and temperature of the acid. Antimony baths. Electro-depositions of antimony are but sel- dom made use of in the industries, though they are very suit- able for the production of contrasts in decorating. Gore dis- covered the explosive power of depositions of antimony chloride, or of antimony containing hydrochloric acid. According to Gore, a bath consisting of tartar emetic 3 ozs., hydrochloric acid 4j^ ozs., tartaric acid 3 ozs., and water I quart, yields a gray crystalline deposit of antimony. This bath requires a current of about 3 volts. The deposit possesses the property of exploding when scratched with a hard object. The explo- ELECTRO- DEPOSITION OF METALS. sion of the deposit is caused by a content of chloride of anti- mony. Bottger found 3 to 5 per cent, of chloride of antimony in the deposit, and Gore 6 per cent. A similar explosive de- posit is obtained by electrolyzing a simple solution of chloride of antimony in hydrochloric acid (liquid butter of antimony, liquor stibii chlorati] with the current. A lustrous non-explosive deposit of antimony is obtained by boiling 4.4 ozs., of carbonate of potash, 2.1 1 ozs., of pulverized antimony sulphide, and I quart of water, for I hour, replacing the water lost by evaporation, and filtering. Use the bath boiling hot, employing cast antimony plates or platinum sheets as anodes. Another antimany bath may be prepared by dissolving freshly precipitated sulphide of antimony with an excess of sulphide of ammonia. It yields a very lustrous and adherent deposit of antimony, which, in 6 to 8 minutes, is of sufficient thickness to bear polishing with Vienna lime upon rapidly revolving cloth wheels. An unpleasant feature of this bath is that during the plating process much sulphur is separated, which renders the bath turbid, so that it has to be frequently filtered. With the use of platinum anodes, this separation of sulphur is, of course, still greater than with antimony anodes. 2. Deposition of Arsenic. Properties of arsenic. Arsenic has a gray-white color, a strong metallic lustre, is very brittle, and evaporates at a red heat. In dry air arsenic retains its lustre, but soon turns dark in moist air. It is scarcely attacked by dilute hydrochloric and sulphuric acids, while concentrated sulphuric acid as well as nitric acid oxidizes it to arsenious acid. If caustic alkalies are fused together with arsenic, a portion of the latter is con- verted into alkaline arsenate. Arsenic baths. Deposits of arsenic are more frequently used than antimony deposits for decorative purposes ; for in- stance, to color gray the dead background of brassed lamp- legs, vases, etc., while the prominent portions are bright brass. DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 347 A solution suitable for depositing arsenic upon all kinds of metals is as follows : I. Pulverized arsenious acid I ^ ozs., crystallized pyrophos- phate of soda 0.7 oz., 98 per cent, potassium cyanide I ^ ozs., water I quart. Dissolve the pyrophosphate of soda and the potassium cyanide in the cold water, and after adding, with stirring, the arsenious acid, heat until the latter is dissolved. In heating, fumes con- taining prussic acid escape, the inhalation of which must be carefully avoided. The bath is used warm, and requires a vigorous current of at least 4 volts, so that, at the least, 3 Bunsen elements have to be coupled for tension. After sus- pending the objects they are first colored black-blue, the color passing with an increased thickness of the deposit into pale blue, and finally into the true arsenic gray. Platinum sheets or carbon plates are to be used as anodes. Instead of a bath prepared according to formula I., a solu- tion of the following composition may be used: II. Sodium arsenate I ^ ozs., 98 per cent, potassium cyanide 0.8 oz., water I quart. Boil the solution for half an hour, then filter and use it at a temperature of at least 167 to 176 F., with a strong current ; it yields a good deposit. Large baths, to be used cold, must be more concentrated, and require a stronger current than hot baths. When the baths begin to work irregularly and sluggishly, they have to be replaced by fresh solutions. In the execution of deposits of arsenic and antimony the same rules are to be observed as for the other electro-plating processes. Deposits of antimony and arsenic by contact and immersion are much used for coloring brass and copper, as well as iron (browning of gun-barrels) and silver. Most frequently a warm solution of antimony trichloride (the butter of antimony of commerce) in hydrochloric acid is used for this purpose, in which the clean and pickled brass articles acquire a coating of a steel gray color with a bluish tinge. By using instead a hot 34^ ELECTRO-DEPOSITION OF METALS. mixture of chloride of arsenic with a small quantity of water, a steel-gray color without a bluish tinge is obtained. By immersing brass in a solution of 20 parts by weight of arsenious acid, 40 of hydrochloric acid, 800 of water, and 10 of sulphuric acid heated to between 122 and 140 F., it becomes black by the separation of pulverulent arsenic ; after rinsing in water and drying the coat adheres quite well. By contact with zinc the deposit is obtained in a shorter time and adheres better. 3. Deposition of Aluminium. Properties of aluminium. Aluminium is a white silvery metal with an almost imperceptible bluish tinge. It is extremely light, the specific gravity being only 2.58, is very malleable and ductile, takes a high polish, and is not liable to tarnish in the air. It melts at about I3OOF. Its principal common impur- ities are iron and silicon. Aluminium does not seem to possess any qualities which would make it advantageous as an electro-deposit upon other metals. Many solutions have been proposed which it was claimed should give good deposits of the metal, but, on trial, have been found to be worthless. The solutions given below are claimed to give good results, but are here mentioned with due reserve. Aluminium baths. I. Bertrand states that he has deposited aluminium upon a plate of copper in a solution of the double chloride of aluminium and ammonium by using a strong current from three Bunsen elements, the bath being worked at 140 F. II. Gaze's process. Mr. Goze obtained a deposit of alumin- ium by the single-cell method from a dilute solution of the chloride. The liquid was placed in a jar in which was im- mersed a porous cell containing dilute sulphuric acid ; an amalgamated zinc plate was immersed in the acid solution and a plate of copper in the chloride solution, the two metals being connected by a copper conducting wire. At the end of some hours the copper plate became coated with a lead-colored de- DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 349 posit of aluminium, which, when burnished, presented the same degree of whiteness as platinum and did not appear to tarnish readily when immersed in cold water or exposed to the atmos- phere, but was acted upon by dilute sulphuric and nitric acids. III. The following formula is given by Mr. Herman Reinbold, who states that it yields excellent results : Dissolve 50 parts by weight of alum in 300 of water, and to this add 10 parts of aluminium chloride. The solution is to be heated to 200 F., and, when cold, 39 parts of potassium cyanide are to be added. A feeble current should be used. IV. A new method for the electro-deposition of aluminium is as follows:* To a 20 per cent, solution of ammonium-alum in warm water add a solution of about the same quantity of pearl- ash and of a small quantity of ammonium carbonate. The mix- ture effervesces and yields a precipitate, which is filtered off and thoroughly washed with water. Over the precipitate thus obtained pour a warm solution of 16 per cent, ammonium-alum and 8 per cent, pure potassium cyanide, and boil the whole in a closed iron vessel for 30 minutes. The proper proportions for the solutions are as follows : First alum solution : Ammon- ium-alum 4 Ibs., warm water 10 quarts. Pearl-ash solution : Pearl-ash 4 Ibs., warm water 10 quarts, ammonium carbonate 4^2 to 5J^ drachms. Second alum solution : Ammonium-alum 8 Ibs., warm water 25 quarts, potassium cyanide 4 Ibs., then add 20 quarts of water and about 4 Ibs., more of potassium cyanide, and let the whole boil for about J^ hour. The filtered solution is then ready for use as the electrolytic bath. As anodes perforated aluminium plates are used, which can be raised and lowered. The cathodes receive the deposit. The bath is maintained at a temperature of between 80 and 149 F. By adding pieces of other metals, such as gold, silver, nickel, copper, etc., to the aluminium anodes, the color of the deposit may be somewhat changed. If the deposit shows a gray coloration it is made lustrous by dipping in a solution of caustic soda, which also prevents oxidation. * Neueste Erfindungen und Erfahrungen, vol. xix., p. 353. 350 ELECTRO-DEPOSITION OF METALS. Several companies, in the past, have been selling sheet iron purporting to be plated, or " galvanized " as they call it, with aluminium or with alloys of aluminium and tin. It is a fact that alloys of aluminium and tin can be coated on sheet iron according to the process outlined as having been carried on by the Tacony Iron & Metal Company of Philadelphia, for plating the iron columns of the Public Buildings of that City, but in most cases sheet iron purporting to be plated with alumin- ium have been found on analysis to contain no aluminium at all. In the plating of the columns of the Philadelphia Public Buildings by the Tacony Iron & Metal Company, the process consisted of plating the metal with an alloy of 75 per cent, aluminium and 25 per cent. tin. The iron columns were first cleansed and then electro- plated with copper in an alkaline bath, a thickness of something like T V inch of copper being obtained in an acid sulphate bath. The aluminium-tin alloy was deposited at a temperature of 130 F., at a current density of 8 amperes per square foot, from pure aluminium -anodes, in a bath having the following composition : Saturated solution aluminate of soda 75 parts, stannate of soda 25 parts. The bath also contained some potassium cyanide. Electro-depositions upon aluminium. The electro-deposition of other metals upon aluminium presents many difficulties which are chiefly due to the behavior of this metal in the plat- ing baths. The deposits to be sure are formed but they possess no adherence, and especially baths containing potas- sium cyanide yield the worst results in consequence of the effect of alkaline solutions upon the basis-metal. Since the production of aluminium has so largely increased and a great number of articles of luxury and for practical use are now made of this metal, the need of decorating such articles by electro- plating or covering them entirely with other metals has been felt, since the color of aluminium is by no means a sympathetic one. Look into a show window where aluminium articles are exposed nothing but gray in gray. Offended, the eye of the observer turns away and seeks a more agreeable rest. DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 351 Aluminium behaves so differently from other metals towards the cleansing agents usually used that different methods from those previously described have to be employed in preparing it for plating. Nitric acid has almost no effect on aluminium, and pickle just as little ; but, on the other hand, the metal is attacked by concentrated hydrochloric acid, dilute hydrofluoric acid, and especially by alkaline lyes. Hence if polished articles of aluminium are to be prepared for plating, alkaline lyes will have to be avoided in freeing them from grease, it being best to use only benzine for the purpose. Unpolished articles may without hesitation be freed from grease with caustic potash or soda lye, and for the production of a dead white surface be for a short time pickled in dilute hydrofluoric acid and then thor- oughly rinsed in running water. For producing an electro- deposit upon aluminium it has been considered advisable to first copper the metal, and the Aluminium Gesellschaft of Neuhausen recommends for this purpose a solution of nitrate of copper. But the adherence of the copper deposit proved also insufficient, because in the subsequent silvering, nickeling, etc., the deposit raised up. The copper bath recommended by Delval, consisting of sodium pyrophosphate 3 ozs., copper sulphate (copper vitriol) y oz., sodium bisulphite ^ oz., water I quart, also proved unreliable. According to a patented process, plating of aluminium is claimed to be effected successfully and without defect by lightly coating the metal with silver amalgam in a silver bath com- pounded with potassium mercury cyanide. However, this treatment also did not always yield reliable results. The best and most reliable process is without doubt the one patented, in 1893, by Prof. Nees. It consists in first immersing the aluminium articles previously freed from grease in caustic soda lye until the action of the lye upon the metal is recognized by gas bubbles rising to the surface. The articles without be- ing previously rinsed are then for a few minutes immersed in a solution of 77 troy grains of chloride of mercury, rinsed, again 35 2 ELECTRO-DEPOSITION OF METALS. brought into the caustic soda lye and then, without rinsing, suspended in the silver bath. The deposit of silver thus ob- tained adheres very firmly, and can be scratch-brushed and polished with the steel without raising up. It can also be directly gilded, brassed, or, after previous coppering in the potassium cyanide copper bath, provided with a heavy deposit of nickel and polished upon polishing disks. The Mannesmann Pipe Works, Germany, produce durable electro-deposits by brushing the aluminium with solutions of sulphide of gold and sulphide of silver in balsam of sulphur* and volatile oils, and burning in the metals in a muffle under exclusion of the air at 840 to 930 F. The thin layers of metal which are separated adhere firmly to the aluminium and are then provided with any electro-deposit desired. According to a process patented by the same corporation the articles are provided with a firmly adhering (?) film of zinc by immersing them in a boiling solution of zinc dust in caustic soda, and are then electro-plated. CHAPTER XIV. 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 separated from the object serving as a mould. Copper is the most suitable metal for galvanoplastic pro- cesses, that which is precipitated by electrolysis showing the following valuable properties : It may be precipitated chemic- ally pure, and in this state is less capable of change than ordi- * Solution of sulphur in linseed oil. GALVANOPLASTY (REPRODUCTION). 353 nary commercial copper or the ordinarily used copper alloys, its strength of extension being 20 per cent, greater than that of melted copper ; its hardness is also greater than that of melted copper, while its specific gravity (8.85) lies between that of cast and rolled copper. The physical properties of copper deposited by electrolysis are dependent on the condition of the bath, as well as on the intensity and tension of the working current. The bath used for precipitating the copper is in all cases a solution of blue vitriol. Smee had originally proved by experiments that copper is obtained as a more tenacious and fine-grained deposit when the current-strength is as great as possible, without, however, evolution of hydrogen taking place ; while copper in pulveru- lent, sandy form is obtained with a current-strength that liber- ates hydrogen, and in coarsely crystalline form when the cur- rent-strength is very slight. At a more recent period, von Hubl instituted a series of systematic experiments for the determination of the conditions under which deposits with different physical properties are ob- tained. Hubl worked with 5 per cent, neutral, and 5 per cent, acid, solutions of copper, as well as with 20 per cent, neutral, and 20 per cent, acid solutions. The neutral solutions were prepared by boiling blue vitriol solution with carbonate of copper in excess, and the acid solutions by adding 2 percent, of sulphuric acid of 66 Be. The result was that in the neutral 5 per cent, solutions less brittle deposits were obtained with a small current-density than in a more concentrated solution, though the appearance of the deposits was the same. The ex- periments with acidulated 'baths confirmed the fact that free sul- phuric .acid promotes the formation of very fine-grained deposits even with very slight^ current-densities, and it appears that the brittleness of copper deposited from acid baths is influenced less by the concentration than by the current-density used. 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 23 354 ELECTRO-DEPOSITION OF METALS. deposits produced by means of the single-cell apparatus, and the other those by the battery or dynamo-machine. I. Galvanoplastic Deposition in the Cell Apparatus. The cell apparatus consists of a vessel containing blue vitriol solution kept saturated by a few crystals of blue vitriol placed in a muslin bag or a small perforated box of wood, stoneware, etc. In this vessel are placed round or square porous clay cells (diaphragms) which contain dilute sulphuric acid and a zinc plate, the zinc plates being connected with each other and with the objects to be moulded which may be either metallic or made conductive by graphite by copper wire or copper rods. The objects to be moulded play the same role as the copper electrode in a Daniell element, and the cell apparatus FIG. 125. is nothing else but a species of Daniell element in which the internal, instead of an external, current is utilized. As soon as the circuit is closed by the contact of the objects to be moulded with the zinc of the 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 GALVANOPLASTY (REPRODUCTION). 355 from the blue vitriol solution and deposited in a homogeneous layer upon the articles to be moulded. A simple apparatus, frequently used by amateurs for mould- ing metals, reliefs, etc., is shown in Fig. 125. In a cylindrical vessel of glass or stoneware filled with satu- rated blue vitriol solution is placed a porous clay cell, and in the latter a zinc cylinder projecting about 0.039 to 0.079 inch above the porous clay cell. To the zinc is soldered a copper ring, as plainly shown in the illustration. The clay cell is filled with dilute sulphuric acid (i 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 supplement the content of copper, small linen or sail-cloth bags filled with blue vitriol are attached to the upper edge of the vessel. Fig. 126 shows another form of cell-apparatus which is much used in printing establishments for the production of FIG. 126. cliches. A is a large box lined with gutta-percha. In this box is suspended a smaller box, B, the bottom of which is formed of a disk of leather or parchment. To the side of this box are nailed strips, b. To these strips is secured a piece of stout linen, which serves partially as a support of the zinc plate Z n and partially to prevent impurities of the zinc from ELECTRO-DEPOSITION OF METALS. falling upon the leather disk. The zinc plate is connected with the strap K, which is made of sheet copper. In the box A lies the board />, which is sufficiently weighted with strips of lead to prevent it from floating in the fluid. To prevent the separation of copper, these lead strips are coated with a varnish made from sealing-wax or with gutta-percha. To the upper side of the board is nailed the copper strap K' , which is insu- lated as far as it touches the fluid and the board by a coating of gutta-percha. The binding screw E connects the two copper straps. A perforated copper sheet bent in the form of a gutter dips above in the copper solution. During the ope- ration this copper sheet is kept filled with crystals of blue vitriol, and serves to maintain a uniform saturation of the fluid. To produce deposits with this apparatus, the first matrice is laid upon the portion of copper strap upon the board D. The copper strap is then connected with the conducting surface by driving a brass pin through the matrice and the strap into the board. Underneath the other end of the matrice is placed a small piece of copper sheet insulated by gutta-percha, so that it projects y 2 to ^ inch beneath the matrice.' It is also brought in contact with the conducting surface by means of a brass pin. Upon this sheet is placed the second matrice, which is also secured with a brass pin, and so on, until all the moulds upon which copper is to be precipitated are upon the board. The surfaces of the moulds, as well as the heads of the pins, are then carefully rubbed with graphite, and the board is brought into the box filled with blue vitriol solution. The box B with the zinc plate is then suspended in the box A, and after filling it with dilute sulphuric acid, the two copper straps are connected by the binding screw E. The electric current then passes through the latter and the pin to the sur- face of the first matrice, and after depositing copper upon it passes through the second pin and the small copper plate to the second matrice, and so on, effecting a uniform deposit of copper upon all conducting surfaces connected with each other. Large apparatus. To cover large surfaces, use large, square GALVANOPLASTY (REPRODUCTION). 357 vats of stoneware, or of wood, lined with lead, gutta-percha, or another substance unacted upon by the bath. For baths up to three feet long, stoneware vats are to be preferred. Fig. 127 shows the French form of cell apparatus. In the middle of the vat, and in the direction of its length, is disposed a row of cylindrical cells, close to each other, each provided with its zinc cylinder. A thin metallic ribbon is connected with all the binding screws of the cylinder, and is in contact at FIG. 127. 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, there- fore, in connection with the zincs. The German form of cell apparattis is shown in Fig. 128. It is provided with long, narrow, rectangular cells of a correspond- ingly 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 centre rod, which lies over the cells, are suspended the zinc 358 ELECTRO-DEPOSITION OF METALS. plates by means of a hook, while the two outer rods serve for the reception of the moulds. FIG. 128. The size of the zinc surfaces in the simple apparatus should be about equal to that of the surfaces to be moulded, if dilute sul- phuric acid (i acid to 30 water) is to be used. For particulars see " Execution of the Galvanoplastic Deposition of Copper." The copper bath for the cell apparatus consists best of a mode- rately saturated solution of pure blue vitrol, free from iron, in water free from lime, and should show about 18 to 20 Be., a bath of 100 quarts requiring about 20 to 24 Ibs. of blue vitriol. The following table gives the approximate content of pure crystallized blue vitriol at different degrees Be., and at 59 F. Degrees, Be. Weight by volume. This solution contains crystallized blue vitriol. c . 3 ] 035 .072 .088 ."3 .121 .130 .138 .147 57 .166 .I 7 6 5 per cent. ii 13 " 17 " 18 " 19 20 21 2 3 24 25 10 12 I cO 16 .. 17 18 :::::::::::::::.::: I Q o . 2QO 21 22 GALVANOPLASTY (REPRODUCTION). 359 While to a copper bath working with the use of an external source of current, more or less sulphuric acid is added, accord- ing to requirement, baths in the single cell apparatus do not require such addition, because a considerable quantity of the acid in the clay cell gradually penetrates by osmose into the bath, and not only of the acid alone, but also of the white vitriol solution formed, whereby the working duration of the bath is considerably reduced. Furthermore, the sulphuric acid liberated by the separation of copper from the blue vitriol finds no saturation ; so that such a bath finally contains an ex- cess of acid which for the production of good deposits must from time to time be removed, if it is not preferred to throw the bath away and make a fresh one. The simplest method of removing the excess of acid is to add to the bath pure carbon- ate of copper as long as strong effervescence takes place, blue vitriol being thereby formed, and hence the bath at the same time strengthened. Some operators remove the excess of acid by adding to the bath whiting free from iron until no more effervescence takes place, and then filtering off from the calcium sulphate (gypsum) formed. The first-mentioned pro- cess is, however, preferable in every respect. 2. Galvanoplastic Deposition by the Battery and Dynamo- Machine. Since it has been shown in the preceding section that a cell apparatus is to be considered as a Daniell element closed in itself, it will not be difficult to comprehend that in economical respects no advantage is offered by the production of galvano- plastic depositions by a separate battery, because in both cases the chemical work is the same and the zinc dissolved by the use of the Daniell or Bunsen element effects no greater quantity of copper deposit in the bath than the same quantity of zinc dissolved in the cells of the single apparatus. In other re- spects the use of a battery, however, offers great advantages. The employment of external sources of current requires the same arrangement as shown in Figs. 52 and 54, pp. 96 and 98 ; 360 ELECTRO- DEPOSITION OF METALS. copper anodes being placed in the bath, which are connected with the anode pole of the battery. By this arrangement, while the copper is being deposited upon the mould, the copper anodes become dissolved by the sulphuric acid set free, forming sulphate of copper, which con- tinued action keeps the copper content of the bath quite con- stant. Furthermore, no foreign metallic admixtures reach the bath, as is the case in the single cell apparatus, by the white vitriol solution penetrating from the clay cell into the bath and causing the formation of rough and brittle deposits of copper. The principal advantage, however, is that by placing a resist- ance board in the circuit the current-strength can be controlled so that the deposits can be quickly covered with a strong current and then augmented with a weaker current, and that by intelligently regulating the current-strength, deep depres- sions can also be covered, which is difficult in the single cell apparatus. A. Depositions with the Battery. The Daniell element described on p. 35, which yields a tension of about I volt, is much liked for this purpose. Since the copper bath for galvanoplastic purposes requires for its de- composition an electromotive force of only 0.5 to I volts, it will be best for slightly depressed moulds to couple the elements for quantity (Fig. 3, p. 20), alongside of each other; and only in cases where the particular kind of moulds requires a current of stronger tension, to couple two elements for tension one after the other, an excess of current being rendered innoxious by means of the resistance board or by suspending larger surfaces. Bunsen elements may, however, be used to great advantage, since the zincs of the Daniell elements become tarnished with copper and have to be frequently cleansed if the process is not to be retarded or entirely interrupted. The Bunsen elements need only be coupled for quantity, their electromotive power being considerably greater. To be sure, the running expenses GALVANOPLASTY (REPRODUCTION). 361 are much greater than with Daniell elements, at least when nitric acid is used for filling. All that has been said under " Electro-plating arrangements in particular," p. 89, in regard to conducting the current, the resistance boards, conducting rod, anodes, etc., is also valid for plants for the galvanoplastic deposition of copper with the battery. B. Depositions with Dynamo- Machines. It is best to use dynamos capable of yielding a large quantity of current with a tension of 2, or, at the utmost, 2^/ 2 volts. In order to avoid repetition, the reader is referred to what has been said under " Arrangements with dynamo-electric ma- chines," p. 109, the directions given there applying also to the galvanoplastic process. Since only in very rare cases the object-surface will be the same in all baths, it will be advisable to supply each of the baths, if several of them are worked with one dynamo-machine, with a resistance-board and a voltmeter. Copper baths for galvanoplastic depositions with a separate source of current. The directions for the composition of the bath vary very much, some authors recommending a copper solution of 1 8 Be. which is brought up to 22 Be. by the addi- tion of pure concentrated sulphuric acid. Others again increase the specific gravity of the bath up to 25 Be. by the addition of sulphuric acid, while some prescribe an addition of 5 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 at disposal, the nature of the moulds, and the distance of the anodes from the objects. The object of adding sulphuric acid is, on the one hand, to render the bath more conductive and, when used in proper pro- portions, to make the deposit more elastic and smoother, and prevent the brittleness and coarse-grained structure which, under certain conditions, appear. When depositing with a battery, somewhat more sulphuric acid may be added to the bath than when employing the current of a dynamo-electric machine. The following compositions have, in most cases, 362 ELECTRO-DEPOSITION OF METALS. been found suitable for the reproduction of shallow as well as of deep moulds. I. For depositing with the dynamo. Blue vitriol solution of 1 8 Be. 100 quarts, pure sulphuric acid of 66 Be. I to I y 2 quarts. II. For depositing with the battery. Blue vitriol solution of 18 Be. 100 quarts, pure sulphuric acid of 66 Be. I ^ to 2 quarts. For some special uses, the composition of the bath has to be somewhat modified, which will be referred to later on. In re- gard to the elasticity, strength and hardness of galvanoplastic depositions of copper, v. Hubl found that copper of great toughness, but of less hardness and strength, is obtained with a current density of 0.6-1.0 ampere from an 18 per cent, blue vitriol solution, and copper of great hardness and strength, but of little toughness, with 2 to 3 amperes, from a 20 per cent, solution. For copper printing-plates, a 20 per cent, solution, com- pounded with 3 per cent, of sulphuric acid, and with the use of a current-density of 1.3 amperes, was found most suitable. Many operators prefer as a bath a solution of pure blue vitriol of 22 Be., without any addition of sulphuric acid. A good deposit is obtained in such a bath, but a tension of 2 to 2^ volts is required, while acidulated baths need only ^ to I J^ volts, according to the content of acid. Very fine deposits have also been obtained in baths consist- ing of a blue vitriol solution of 21 Be, brought up to 22 by the addition of sulphuric acid. This shows that it is not neces- sary to stick to a fixed unlimited composition of the baths, provided it is understood how to bring the current-condition into harmony with the composition. According to the composition of the bath, a fixed minimum and maximum current-density correspond to it, which must not be exceeded if useful deposits are to be obtained. There is, however, a further difference according to whether the bath is at rest or in motion, v. Hubl obtained the following results : GALVANOPLASTY (REPRODUCTION). 363 Composition of solution. Minimum and maximum current-density per 15.5 square inches. With solution at rest. Amperes. With solution in gentle motion. Amperes. 15 per cent, blue vitriol, without sulphuric 2.6 to 3.9 1-5 " 2 '3 3-4 " 5-i 2.0 " 3.0 3.9 to 5.2 2.3 3.0 5.1 6.8 3.0 " 4.0 15 per cent, blue vitriol, sulphuric 3-cid with 6 per cent. 20 per cent, blue vitriol, without sulphuric 20 per cent, blue vitriol, with 6 per cent. 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 preceding table shows that a copper bath in gentle motion can stand considerably higher current densities, and hence will work with correspondingly greater activity than a bath at rest. In the electrolytic refining of copper it was found that for the faultless deposition of copper the bath must be maintained entirely homogeneous in all its parts. When a copper bath is at rest and the depositing operation in progress, the upper layers of the bath become poorer in copper than the lower, while at the same time they contain more sulphuric acid. This difference in the composition of the upper and lower layers has the disadvantage that the portions dipping into the layers richer in copper become more thickly coppered than those in the upper layers. Baths which are constantly in gentle motion show less inclination to the formation of knots and other rough excrescences, and hence the current- density may be greater than with solutions at rest resulting in the deposition being effected with greater rapidity. These experiences gathered in electro-metallurgical operations on a large scale, have been advantageously applied to galvanoplasty. The constant motion of the copper bath may be effected in ELECTRO-DEPOSITION OF METALS. various ways. Stirring by hand is frequently relied upon, but it is liable to be accidentally omitted, and being of necessity intermittent allows time for partial separation to occur be- tween two consecutive stirrings. Mechanical agitation, which is more certain in its effects, may be applied by working a small screw propeller slowly at one end of the bath, or by blowing air into the solution constantly through a tube passing to the bottom of the vat, by means of a fan-blower or other arrange- ment. Where many copper baths are in operation, the agitation of the bath may be effected as follows : The baths are arranged in the form of steps ; near the bottom each bath is provided with a leaden outlet-pipe (Fig. 129), which terminates over the next bath over a distribut- ing gutter, or as a perforated pipe, //. From the last bath the copper solution flows into a reservoir, E, from which it is forced' by means of a hard- rubber pump, z, 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, GALVANOPLASTY (REPRODUCTION). 365 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. Whatever motion is given to the bath it must be sufficiently vigorous to insure thorough mixture of the solution, but with- out disturbing the relative positions of anode and cathode, and the mechanism must be so applied that it in no way lessens the facilities for examining the progress of deposition. Annealed sheets of pure copper are used as anodes ; impure anodes introduce other metallic constituents into the bath, which might result in a brittle deposit. 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 should ' present at least as large a surface as the cathodes ; for flat moulds the distance between them and the anodes may be two to three inches, but has to be increased for deeper .moulds. The copper withdrawn from the bath by deposition being only partially replaced by the anodes, the con- tent of free acid will increase in consequence of the reduction of the content of copper. However, the copper wanting can 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. Determination of free acid. The free acid is determined by titrating the copper solution with normal 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 glass, dilute with the same quantity of distilled water, and add drop by drop from a burette normal soda solution, stirring con- stantly, until congo paper is no longer colored blue, when moistened with a drop of the solution in the beaker glass. The cubic centimeters of normal soda solution consumed multiplied by 4.9 gives the number of grammes of sulphuric acid in the liter. Suppose up to the appearance of the final reaction by means 366 ELECTRO-DEPOSITION OF METALS. of congo paper, which indicates that all the free sulphuric acid has been saturated by the normal soda solution, 11.99 cubic centimeters of normal soda solution had been used for TO cubic centimeters of copper bath, then one liter of the bath contains 11.9x4.9 = 58.31 grammes of sulphuric acid. Determination of the content of copper according to Hacn. This method is based upon the conversion of blue vitriol and potassium iodide into copper iodide and free iodine. By de- termining 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 calculation. The process is as follows : Bring 10 cubic centimetres of the copper bath into a measuring flask holding T \ liter, neutralize the freed acid by the addition of dilute soda lye until a precipitate of bluish cupric hydrate, which does not disappear even with vigorous shaking, commences to separate. Now add, drop by drop, dilute sulphuric acid until the precipitate 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 centimetres by means of a pipette into a flask of 100 cubic centimetres' capacity and provided with a glass stopper; add 10 cubic centimetres 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 con- stant stirring, a decinormal solution of sodium hyposulphite until starch-paper is no longer colored blue by a drop of the solution in the flask. Since I cubic centimetre of deci- normal solution corresponds to 0.0249 grammes of blue vitriol (=0.0063 gramme of copper), the content of blue vitriol in one liter of the solution is found by multiplying the number of cubic centimetres of decinormal solution consumed by 24.9. For the correctness of the result it is necessary that the copper bath should be free from iron. Suppose 7.2 cubic centimetres of decinormal solution of sod- ium hyposulphite have been used, the bath would contain 7.2 x 2 4-9 = 179.28 grammes of blue vitriol. GALVANOPLASTY (REPRODUCTION). 367 If now by these two determinations, the content of free acid and of blue vitriol in the bath has been ascertained, a com- parison 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 carbonate of copper 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 carbonate of copper have to be added, and each gramme of carbonate of copper 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 carbon- ate of copper 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. Preparation of moulds (matrices"} in plastic material. If a negative of the original for the production of copies is not to be made by direct deposition upon a metallic object, the negative has to be prepared by moulding the original in a plastic mass, which on hardening will retain the forms and lines of the design to the finest hatchings. Gutta-percha, wax (stearine, etc.), plaster of Paris, glue, and a few readily fusible metals are suit- able materials for this purpose. Since the galvanoplastic process as far as it applies to electro- typing, will next be considered, we first direct our attention to the preparation of moulds or matrices of gutta-percha and wax, the only materials suitable for this purpose, and which are generally used. I. 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 fibres, 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 ELECTRO-DEPOSITION OF METALS. plastic by heating, without, however, becoming sticky, and finally it should rapidly harden. The most simple way of softening gutta-percha is to place it in water of 176 to 194 F. When thoroughly softened no hard lumps should be felt in kneading with the hands, in doing which the latter should be kept thoroughly moistened with water. A fragment corresponding to the size of the object to be moulded is then rolled into a plate about J^ to ^ inch thick. To facilitate the detachment of the mould after cooling, the surfaces of the objects to be moulded, as well as the side of the gutta-percha which is to receive the impression, should be well brushed with black-lead (plumbago or graphite). The black- leaded surfaces are then placed one upon the other, and after gently pressing the gutta-percha with the hand upon the original the whole is placed in the press. To stop the further movement of the press-plate and prevent injury to the mould by too strong a pressure, small iron blocks, somewhat higher than the frame containing the object to be moulded and the gutta-percha plates are placed on both sides of the frame. The screw of the press is then made to act until the press-plate touches the iron blocks ; under this pressure the gutta-percha is allowed to cool and harden. For making the impression of the form in the moulding com- position, a moulding press is used which is capable of giving a gradual and powerful pressure. Fig. 130 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 swung on pivots and counter-balanced by a heavy-weight, as shown, so that it can be readily thrown up, leaving the bed exposed, the black-leaded type-form being placed on the bed. The well black-leaded case is attached by clamps to the movable head, or the form (also black-leaded) is laid face down on the case, and the head is then turned down and held in place by the swinging bar (shown turned back in the cut). All being ready, the toggle-pressure is put on by means of the hand-wheel and screw, the result being to raise GALVANOPLASTY ( REPRODUCTION) . 369 the bed of the press with an enormous pressure, causing the face of the type-form to impress itself into the exposed mould- ing surface. FIG. 130. Fig. 131 represents a form of " hydraulic press" less com- monly used than that just described. It is provided with pro- jecting rails and sliding plate, on which the form and case are arranged before being placed in the press. The pump, which is worked by hand, is supported by a frame-work on the cistern below the cylinder, and is furnished with a graduated adjust- able safety-valve to give any desired pressure. 24 ELECTRO-DEPOSITION OF METALS. FIG. 131. 2. Moulding in wax (stearine). Beeswax is a very useful material for preparing moulds, but, like stearine, it is accord- ing to the temperature now softer and now harder, which must be taken into consideration. In the cold, pure beeswax is quite brittle and apt to become full of fissures in pressing. To decrease the brittleness certain additions are made to the wax, Urquart recommending the following mixture, which is fre- quently used in England: Beeswax 85 parts by weight, Venice turpentine 13, black-lead finely pulverized 2. According to Volkmer, a good mixture is obtained by melt- ing together 70 parts of wax and 30 of stearine. Watt prefers a mixture consisting of 70 parts of wax, 26 of stearine, and 4 of litharge or flake-white. G. L. v. Kress recommends the following mixture: White wax 42.32 ozs., stearine 14.11 to 21.16 ozs., tallow 10.58 ozs., graphite 1.76 ozs. First melt the asphalt over a moderate fire, then add the wax, stearine, and GALVANOPLASTY (REPRODUCTION). 371 tallow, and when these are melted, the graphite ; stir until the mixture begins to congeal. To prepare the wax mould pour the melted composition into flat metallic trays provided with loops for suspension in the bath. When the composition is nearly set remove any bubbles of air or impurities from the surface with blotting- FIG. 132. paper. After black-leading the surface press the original, also black-leaded, upon the composition and submit the whole to pressure until cold. When the black-leading has been care- fully done there is no difficulty in detaching the original after cooling ; many operators slightly oil the surface of the original instead of black-leading. 3/2 ELECTRO-DEPOSITION OF METALS. When the mould of gutta-percha or wax has been properly made, it is thoroughly black-leaded in order to give it a con- ducting surface upon which the electro-deposition of the copper may take place. Black-leading must be very thorough so that the black-lead penetrates into every line and letter of the mould, otherwise the copper deposited on the surface will be an im- perfect copy of the original, and it will be useless to place the mould in the bath. The black-lead used in every stage of the electrotyping process must be of the purest description and in the most minute state of division. The best material for the purpose is prepared from the purest selected Ceylon graphite, which is ground by rolling with heavy iron balls until it is re- duced to a dead-black, impalpable powder. Black-leading the moulds is performed either by hand or more commonly by machines. Fig. 132 shows one of these machines with its cover removed to exhibit its construction. It has a traveling carriage holding one or more forms, which passes backward and forward, under a laterally vibrating brush. Beneath the machine is placed an apron which catches the powder, which is again used. Another construction of a black-leading machine is shown in Fig. 133, 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 laterally, vibrating motion. The black-leading space being closed air-tight, scat- tering of black-lead dust is entirely prevented, the excess of black-lead collecting in a vessel placed in the pedestal. On account of the dirt and dust caused by the dry process of black- leading, some electrotypers prefer the wet process in- vented by Mr. Silas P. Knight, of New York. This process is designed to work more quickly and neatly, producing moulds that are thinly, evenly, and perfectly covered. The moulds are placed upon a shelf in a suitable receptacle, and a rqtary pump forces an emulsion of graphite and water over their surfaces through a traveling fine-rose nozzle. This process is pro- nounced to be rapid, efficient, neat, and economical. GALVANOPLASTY (REPRODUCTION). 373 With very deep forms of type, it is sometimes of advantage to first coat the black-leaded surface with copper, in order to obtain a uniform deposit in the bath. The process is as fol- lows : Pour alcohol over the black-leaded form, let it run off and then place the form horizontally over a water trough. Now pour over the form blue vitriol solution of 15 to 1 6 Be., dust upon it from a pepper-box some impalpably fine iron fil- FIG. 133. ings 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 treatment remain uncoppered, the operation is repeated. The excess of copper is washed off and the form, after being provided with the neces- sary 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 y its weight of finest white bronze powder from finely 374 ELECTRO-DEPOSITION OF METALS. 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. After black-leading the workman takes one or several stout copper wires, the ends of which, after thorough cleansing, he heats for an instant, and imbeds them in the wax on the side of the mould. The surface of this wire is carefully exposed, and by way of precaution the place is rubbed with black-lead with the finger to restore the black-lead surface that may have been disturbed. Trifling as this circumstance of exposing the im- bedded wire may appear, the galvanic deposit of the copper on the face of the mould would be impossible were it ne- glected, as the mass of wax being a non-conductor of elec- tricity a galvanic current could not otherwise be established. The exposure of the wire, therefore, is essential in order that the surface of the mould may be rendered properly conductive to insure the uniform deposition of copper upon it. To con- fine the deposit of copper where it is actually desired, and to prevent it from unnecessarily spreading over the edges of the mould, a tool called the " building iron" is heated and run over the mould so as to destroy the continuity of the black- lead surface, save where the deposit of copper is wanted. In order that the deposition of copper may be as nearly uni- form in thickness as possible over the entire surface of the mould, it becomes necessary, where a large surface is to be coated, to provide as much metallic surface as possible on which the deposit of copper may commence and spread. One method of accomplishing this, is to attach one or more pieces of metal to the wax on the edges of the mould, and connect them with the slinging wires by good metallic connections. A very practical device in this connection is the " electric- connection gripper " of Messrs. R. Hoe & Co., of New York. This arrangement is designed to hold and sustain the moulding case, and at the sane time to make an electric connection with the prepared conducting face of the mould only; consequently, GALVANOPLASTY (REPRODUCTION). 3/5 leaving the metal case itself entirely out of the current, so that no copper can be deposited on it. Gutta-percha being specifically lighter than water, moulds of this material have to be provided with a piece of heated lead stuck to the back to prevent them from floating, and to force them to occupy a perpendicular position opposite to the anodes. The moulds are suspended in the bath in the same manner as in other galvanic processes, special care being had that their surfaces hang parallel to the anodes, so that all portions may receive a uniform deposit. Before placing the mould in the bath, pour over it, while in a horizontal position, a mixture of equal parts of alcohol and water ; by this means, a uniform moistening of the mould in the bath is attained, and the settle- ment of air-bubbles on it prevented. For the production of a dense, coherent, and elastic deposit in the acid-copper bath, the chief requisite is to have the current-strength in the correct proportion to the surface to be coated, this applying to deposition with the single-cell appar- atus, as well as with an external source of current. The stronger the sulphuric acid in the clay cells of the simple apparatus is, with the greater rapidity it acts upon the zinc plates, and the more quickly is the copper deposited upon the moulds. If the zinc surface of the clay cells is very large in proportion to the surface of the moulds, the deposition of copper also takes plane with correspondingly greater rapidity. However, a rapid deposition of copper is to be avoided, if de- posits possessing the above-mentioned desirable properties are to be obtained, because a deposit forced too much, turns out incoherent, lacking in density, is frequently blistered, and, with too strong action, is even pulverulent. The color of the deposit furnishes a certain criterion for its quality ; a red- brown color indicating an unsuitable deposit, and a beautiful rose color a good serviceable one. One part of concentrated sulphuric acid of 66 Be. to 30 of water has formerly been given as the proper proportions for the dilute acid used for filling the clay cells, provided the zinc 3/6 ELECTRO-DEPOSITION OF METALS. surface be about the same as that of the moulds. If the zinc surface is smaller than that of the moulds, stronger acid may be used ; but if it is larger, the acid will have to be more dilute. The correct concentration of the acid in the clay cells may be readily determined by the progressive result of the de- posit and its color. Deep moulds require a stronger current, and hence acid of greater strength than flat moulds ; however, if after such deep moulds are provided with a preliminary deposit, the current proves too strong for the correct progress of the operation, its action may be weakened by either dilut ing the acid in the clay cells with water, or by taking out a few zinc plates, or by hanging a few copper sheets upon the object- rods, or suspending more moulds. For the deposition of copper with a separate source of current (battery or dynamo), the same that has been said above applies as regards the current-strength, which must be brought to a suitable degree by the resistance board. The most suitable current-density for the production of a good deposit is 1.5 to 2 amperes per 1^/4 square inches of surface of moulds for baths for depositions with a separate source of current, given on page 362, if at rest, and 2 to 3 amperes if in motion. Since even for deeper moulds a tension of 1.5 volts suffices, if the bath is acidulated, the more powerful Bunsen elements will have to be coupled alongside one another, but two of the weaker Daniell or Lallande elements one after the other, and of such groups, as many as are required will have to be coupled alongside one another for quantity of current (see page 20), to make the active zinc surface nearly equal to that of the moulds. However, for flat moulds coupling the separate weaker elements alongside one another is also sufficient. When the moulds are coated with copper on every side, and also the deeper portions, the current is weakened if a copper deposit of pulverulent or coarse-grained structure and of a dark color should appear on the edges of the moulds, and it is feared that the deposit upon the design or type might also turn out pulverulent. The cur- rent, however, should only be sufficiently weakened to prevent GALVANOPLASTY (REPRODUCTION). 377 a further progress of the dark deposit on the edges towards the interior of the surface of the mould. If, however, by too strong a current the separation of a pulverulent deposit upon the de- sign has already taken place, the deposit may generally be saved; if the fact is noticed in time, and the current correspond- ingly weakened, as the layers are firmly united by the coherent copper then deposited. The current of the dynamo-machine must also be sufficiently weakened by the resistance board in front of the bath, or by that of the machine to guarantee the good quality of the deposit. For deeper moulds the tension for covering may amount to I or 1.5 volts, and for very deep and steep moulds to 1.5 or 2 volts. But when the moulds are completely covered the cur- rent is reduced to about 0.75 volt,* and the operation finished with this tension. . The average time required for the production of a sufficiently heavy deposit with the dynamo-machine is from 7 to 8 hours. In this time the deposit acquires a thickness of about ^ milli- metre (0.013 inch), which corresponds to a weight of about 25 grammes (14.11 drachms) of copper per 15^ square inches. Now, since it frequently happens that an electrotype has to be finished and delivered in a hurry, the work may have to be continued during the night; but as it may not be desirable to have the dynamo running, either a cell apparatus or accumu- lators have to be employed. In using a cell apparatus, it is advisable to first quickly coat the moulds by the current of the dynamo, and then finish the deposit in the apparatus. In modern times accumulators have been successfully used for the same purpose. A detailed description of the accumulators and directions for their treatment may here be omitted, they being furnished by the manufacturers of the various systems. Each accumu- lator consists of a number of alternately positive and negative lead plates immersed in a vessel filled with dilute sulphuric * These current-strengths refer to formulae I. and II. given on page 362. 3/8 ELECTRO-DEPOSITION OF METALS. acid. By conducting the current of a dynamo-machine into the accumulator so that the positive current passes into the positive plates, and the negative current into the negative plates, lead peroxide is formed upon and in the porous posi- tive plates by the co-operation of the sulphuric acid and the oxygen appearing on the positive pole, and the greater the quantity of lead peroxide thus formed, the more electricity is stored in the accumulators. These operations are called charg- ing the accumulator. By interrupting the introduction of a current and closing the circuit of the positive and negative plate systems by the introduction of electrodes in an electro- lyte (galvanic bath), a current is developed whereby the lead peroxide of the positive plates which has been formed is re- duced to lead, while the negative plates are oxidized to lead peroxide. This process is termed discharging. The chemical processes appearing thereby are of more complicated nature than here given, but are omitted so as to render comprehension of the process less difficult The directions for charging and discharging the accumulator must be strictly followed, and re- quire great attention, as charging with too strong a current, or a too abundant discharge may cause the rapid destruction of the plates. The charging is best done during the day with a special small dynamo. The electro-chemical process of forming storage batteries, although discovered in Europe many years ago, has only been developed during the last six or eight years. Since then it has constantly been growing in favor until now, as made in this country, the electro-chemically formed storage battery has strength through the proper adjustment of its mechanical parts, durability by reason of the quantity and quality of material used therein, high efficiency through the purely electro-chemical action given by a special process, and large capacity for its weight by reason of the deep and thorough formation of the active material. The diagram, Fig. 134, shows the connections of a plant as installed by the Electro-Chemical Storage Battery Co., of New York City. VERSITT GALVANOPLASTY (REPRODUCTION). FIG. 134. 379 380 ELECTRO-DEPOSITION OF METALS. By suitable manipulation of the switches and rheostats it is possible to make the following connections: i. The dynamo alone can be used on the baths. 2. The batteries alone can be used on the baths. 3. The dynamo can be used on the baths and the batteries charged with the excess-current, while at the same time steadying the dynamo current. 4. The dynamo and batteries can be used in multiple on the baths, giving a greatly increased capacity. Detaching the deposit from the mould. When the mould has received a suitable deposit, it is taken from the bath, rinsed in water, and all edges which might obstruct the detachment of the deposit from the mould are removed with a knife. From gutta- percha moulds the deposit is gradually lifted by inserting under one corner a flat horn plate or a thin dull brass blade and ap- plying a very moderate pressure ; particles of gutta-percha which may remain adherent are carefully burnt off over a flame. Wax moulds are placed in an inclined position, and a stream of hot water is poured over the copper surface, by which means the wax is sufficiently softened to allow the shell of copper to be stripped off. This may be done by taking hold of one cor- ner of the shell and quickly lifting it as the hot water flows over it. In removing the shell care should be taken to keep it straight, as otherwise it will be difficult to back and finish it properly. Backing the deposit or shell. The tinning of the back of the shell is the next operation, and has for its object to strengthen the union between the shell and the backing metal. For this purpose the back of the shell is cleansed by brushing with ''soldering fluid," made by allowing muriatic acid to take up as much zinc as it will dissolve, and diluting with about J^ of water, to which some sal ammoniac is sometimes added. Then the shell, face down, is heated by laying it upon an iron solder- ing plate, floated on 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- GALVANOPLASTY (REPRODUCTION). 381 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- FIG. 135. 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 382 ELECTRO-DEPOSITION OF METALS. 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. Finishing. For this purpose the plates go first to the saw table (Fig. 135), for the removal of the rough edges by means of a circular saw. The plates are then shaved to take off any FIG. 136. 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. 136 and 137, Fig. 136 being a shaving machine with steam one way, and Fig. 137 one with GALVANOPLASTY (REPRODUCTION). 383 steam both ways. The flatness of the plates is then tested with a straight edge and any unevenness rectified by gentle blows with a polished hammer, taking every care that the face be not damaged. 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. Book-work is generally not mounted on FIG. 137 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. Finally, it remains to say a few words about the process by which a copy may be directly made from a metallic surface without the interposition of wax or gutta-percha. If the me- 384 ELECTRO-DEPOSITION OF METALS. tallic 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. Hence, the metallic original must first undergo special preparation, so as to bring it into a condition favorable to the detachment 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 sulphide of silver is formed, which is a good conduc- tor, but prevents the adherence of the deposit to the original. For the purpose of silvering, free the surface of the metallic original (of brass, copper, or bronze) from grease, and pickle it by washing with dilute potassium cyanide solution (i part potassium cyanide to 20 water.) Then brush it over with a solution of 4^ drachms of nitrate of silver and I 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 sulphide of silver is effected accord- ing to the process described later on (p. 393). The negative thus obtained is also silvered, made yellow with sulphuretted hydrogen, and a deposit of copper is then made, which repre- sents 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 separation of copper on the back of the me- tallic original to be copied, it is coated with asphalt lacquer, which must be thoroughly dry before bringing into the bath. When the deposit of copper is of sufficient thickness, the plate is taken from the bath, rinsed in water, and dried. The edges are then trimmed off by filing or cutting to facilitate the sepa- ration of the shell from the original. Of course only metals which are not attacked by the acid copper solution can be directly brought into the bath. Steel GALVANOPLASTY (REPRODUCTION). 385 plates must therefore first be thickly coppered in the alkaline copper bath, and even this precaution does not always protect the plate from corrosion. It is therefore better to produce in a silver bath (formula L, p. 249) 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. Electro-etching. The lines produced by the ordinary process of etching actually represent, when viewed under the micro- scope, a continuous series of irregular depressions and small cavities, and when some depth is required they are apt to be corroded underneath, and to increase so much in width that the plates are frequently spoiled. None of these objections applies to the galvanic process of etching, which is the invention of Thomas Spencer. Each line, when viewed under the micro- scope, represents a perfect furrow, and is just rough enough for instance, in the preparation of printing plates to hold the printing ink. Lines of considerable depth may be produced without the danger of extending in width or corroding under- neath. The corners of the intersection of two lines are as sharp as if the lines were engraved. A chief requisite for electro-etching is a good etching ground, since it may fre- quently happen that the latter may answer very well for the ordinary process, but is not capable of offering sufficient re- sistance to the electric current. A great advantage in electro- etching is that the solvent is always of the same strength, and, therefore, constant in its action, and that there is no evolution of acid vapors which are injurious to the respiratory organs. The operation of electro-etching is conducted as follows : A conducting wire is soldered with tin solder to the object, and the latter is then coated with the etching ground. The design is then traced with a graver, taking care that the tool lays bare the metal in all the lines. The object thus prepared is con- nected with the positive pole and suspended in the bath, while 25 386 ELECTRO-DEPOSITION OF METALS. a plate of the same metal as the object is secured to the nega- tive pole. The bath consists of a dilute acid corresponding to the metal of the object. For silver, dilute nitric acid is used ; for gold and platinum, water acidulated with aqua regia ; for copper, brass, and zinc, water acidulated with sulphuric acid ; and for tin, water acidulated with hydrochloric acid. Baths containing the metal to be etched in solution, however, work better than acids diluted with water. Thus, for gold and platinum, chloride of gold and platinic chloride are used ; for silver, solution of nitrate of silver ; for copper and brass, solu- tion of blue vitriol ; for iron and steel, solution of green vitriol, or of ammonium chloride, or a combination of both ; for zinc, solution of white vitriol or of chloride of zinc, etc. There are besides various metallic salts suitable for etching by themselves or in combination with the above-named salts. As etching ground various compositions may be employed, it being, however, best to use, if possible, one which can be readily removed. A mixture of equal parts of asphalt and copal varnish forms a good etching ground ; also a composi- tion obtained by melting together asphalt 2j^ parts, wax 2, rosin I, and black pitch 2. However, the following composi- tion, which resists 25 per cent, nitric acid, is to be preferred. It is prepared as follows : Melt yellow wax 4 parts, Syrian asphalt 4, black pitch I, and white Burgundy pitch I. When the mixture boils gradually add, with constant stirring, 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. Since the current- strength is under perfect control, the etch- ing may be carried to any depth desired. Some portions may be less etched than others by taking the plate from the bath, and, after washing and drying, coating the portions which are not to be further etched with lacquer, and returning the plate to the bath. Printing plates on relief may in this manner be prepared by GALVANOPLASTY (REPRODUCTION). 387 slightly etching the bared design of a copper-plate in the gal- vanoplastic copper bath, and then bringing the plate as object in contact with the negative pole, while a plate of chemically pure copper serves as anode. The deposited copper unites firmly with the rough copper of the etched plates, and after re- moving the etching-ground with benzine or oil of turpentine the design appears in relief. Heliography. By this term are understood several methods of printing, in which plates of asphalt, chrome gelatine, etc., produced by exposure to light, are used. For our purposes only the method is of interest by which from the negative, pro- duced by the action of light, a galvanoplastic reproduction printing plates in high and low relief in metal is made. The heliographic process invented by Pretsch and improved by Scamoni, consists in taking by photography a good negative of the engraving or other object to be reproduced, developing with green vitriol, reinforcing with pyrogallic acid and silver solution, and then fixing with sodium hyposulphite solution in the same manner as customary for photographic negatives. A further reinforcement with chloride of mercury solution then takes place until the layer appears light gray. Now wash thoroughly and intensely blacken the light portions by pouring upon them dilute potassium cyanide solution. As in the photo- graphic process, the solutions must be applied in abundance and without stopping, as otherwise streaks and stains are formed. After washing, the plate is dried, further reinforced, and finally coated with colorless negative varnish. From this negative a positive collodion picture is taken, which is in the same manner developed, reinforced, and fixed, the reinforce- ment with pyrogallic acid being continued until the picture is quite perceptibly raised. After careful washing, pour upon the plate quite concentrated chloride of mercury solution, which has to be frequently renewed, until the picture, at first deep black, acquires a nearly white color, and the lines are percept- ibly strengthened. Now wash with distilled water, next with dilute potassium iodide solution, and finally with ammoniacal 388 ELECTRO-DEPOSITION OF METALS. water, whereby the picture acquires first a greenish, then a brown, and finally a violet-brown color. After draining, the plate may progressively be treated with solutions of platinum chloride, gold chloride, green vitriol, and pyrogallic acid, the latter exerting a solidifying effect upon the pulverulent metallic deposits. The metallic relief is now ready ; the layer is slowly dried over alcohol, and the plate, when nearly cold, quickly coated with a thin rosin varnish, which, after momentary dry- ing, remains sufficiently sticky to retain a thin layer of black lead, which is applied with a tuft of cotton. The edge of the plate is finally surrounded with wax, and, after being wired, the plate is brought into the galvanoplastic copper bath to be re- produced. Galvanoplastic reproduction of busts, vases, etc. For this pur- pose an entirely different process of preparing the moulds than that described for electrotyping is required, the material for moulding depending on the nature of the original. Besides gutta-percha and wax, readily fusible metals, plaster of Paris, and glue will have to be considered. If the original bears heat- ing to about 230 F., a copy in one of the readily fusible alloys given later on may be made ; if it will stand heat and pressure, it is best to mould in gutta-percha; but if neither heat nor pressure can be applied, the moulds will have to be executed in plaster of Paris or in glue. The manner of moulding and the material to be chosen furthermore depend on whether surfaces in high relief or round plastic bodies are to be copied, whether projecting portions are undercut, and whether the mould can be directly detached, or, if this is not the case, whether the original has to be dissected and moulded in sepa- rate parts. Regarding the practice of moulding, the reader is referred to special works on that subject; only the main points for the most frequently occurring reproductions will here be given. Surfaces in relief and not undercut are readily moulded in an elastic mass such as gutta-percha or wax ; however, undercut reliefs and especially round plastic objects mostly require a GALVANOPLASTY (REPRODUCTION). 389 plaster-of- Paris mould and are generally dissected ; the dis- section being of course not carried further than absolutely necessary, because the separate parts must be united by a soldering seam which requires careful work, and the seam itself must be worked over and made invisible. Hence the section should as much as possible be made through smooth surfaces, edges, etc., where the subsequent union by a solder- ing seam will prove least troublesome, while cutting through ornaments or through portions, the accurate reproduction of which is of the utmost importance, should be avoided. Heads and busts are always executed in a core mould and in portions unless the entire figure is to be deposited in one piece in a closed mould. The section is made either through the centre line of the head through the lose, which, however, makes the subsequent union very troublesome, if the copy is to be an exact reproduction of the original, or the mould is divided from ear to ear, which has the disadvantage that the deepest part of the mould corresponding to the nose receives the thinnest deposit. It has, therefore, been proposed to make two cuts so that three portions are formed ; one cut from one ear at the commencement of the growth of hair to the other ear ; and the second cut from one ear in a downward direction below the lower jaw in the joint of the head and neck, through this joint below the chin, and then upwards to the other ear, and in front of it to where the hair begins. In bearded male heads the cut follows the contour of the beard and not the joint on the neck behind the beard. To mould round articles in gutta-percha, the softened gutta- percha is kneaded with wet hands upon the oiled original, or, in order to avoid some portions receiving a stronger pres- sure than others, and to insure a layer of gutta-percha of uni- form thickness upon all portions, the moulding may also be executed in a ring or frame of iron or zinc under a press. For the rest, all that has been said in regard to moulding in gutta-percha on p. 367 is also applicable. The following metallic alloys have been proposed for the preparation of moulds : 390 ELECTRO-DEPOSITION OF METALS. I. Lead 2 parts, tin 3, bismuth 5 ; fusible at 212 F. II. Lead 5, tin 3, bismuth 8; fusible at 185 F. III. Lead 2, tin 2, bismuth 5, mercury I ; fusible at 158 F. IV. Lead 5, tin 3, bismuth 5, mercury 2 ; fusible at 127.5 F. The advantage of metallic moulds consists in the metal being a good conductor of electricity, in consequence of which heavy deposits of greater uniformity can be produced than with non-metallic moulds which have been made conductive by black lead. Nevertheless, they are but seldom employed, on account of the crystalline structure of the alloys and the difficulty of avoiding the presence of air bubbles. Bottger claims that a mixture of lead 8 parts, tin 3, and bismuth 8, which is fusible at 227 F., shows a less coarse-grained structure. Fusible alloys containing mercury should not be used for taking casts of metallic objects iron excepted as these will amalgamate with the mercury and be injured. Moreover, copper deposits obtained upon such alloys are very brittle, which is due to the combination of the mercury with the de- posited copper. For moulding with metallic alloys place the oiled object at the bottom of a flat vessel and pour the liquid metal upon it; or pour the liquid metal into a box, remove the layer of oxide with a piece of stout paper, and when the metal is just begin- ning to congeal firmly press the object in it. Plaster of Paris is used for making casts of portions from originals which are so strongly undercut that a mould consist- ing of one piece could not be well detached from them. For taking casts from metallic coins and medals or from small plaster reliefs, it is a very convenient material. The mode of procedure is as follows : After the original model, say a medal, has been thoroughly soaped or black-leaded, wrap round the rim a piece of sufficiently stout paper or thin lead foil, and bind it in such a manner by means of sealing-wax that the face of the medal is at the bottom of the receptacle thus formed. Then place the whole to a certain depth in a layer GALVANOPLASTY (REPRODUCTION). 39 1 of fine sand, which prevents the escape of the semi-fluid plaster of Paris between the rim of the medal and the paper. Now mix plaster of Paris with water to a thin paste, take up a small quantity of this paste with a pencil or brush and spread it in a thin film carefully and smoothly over the face of the medal, then pour on the remainder of the paste up to a proper height and allow it to set. After a few minutes the plaster heats and solidifies. Then remove the surrounding paper, scrape off with a knife what has run between the paper and the rim of the medal, and carefully separate the plaster cast from the model. If instead of applying the first layer with a brush, the whole of the plaster were run at once into the receptacle, there would be great risk of imprisoning air bubbles between the model and the mould, which would consequently be worthless. The mould is finally made impervious and conductive accord- ing to one of the methods to be described later on. The moulding in plaster of Paris in portions, when casts from large plastic objects with undercut surfaces and reliefs are to be taken, is troublesome work, because each separate mould must not only be so that it can be readily separated without injury to the original, but must also fit closely to its neighbors. Hence thought and judgment are required to see of which parts separate moulds are to be made, or, in other words, in how many parts the mould is to be made. After determining on the plan of the work, the mode of procedure is as follows : Oil a portion of the object, if it consists of metal, or soap it, if of plaster of Paris, marble, wood, etc., and apply by means of a brush a thinly-fluid paste of plaster of Paris, taking care that no air bubbles are formed by the strokes of the brush. When this thin coat is hard, continue the application of plaster of Paris with a horn spatula until the coat has acquired a thick- ness of y^ to i inch, and allow it to harden. Then separate the mould, and after cutting or sawing the edges square and smooth, replace it upon the portion of the original model cor- responding to it. Now oil or soap the neighboring portions of the model, and at the same time the smooth edges of the first 392 ELECTRO-DEPOSITION OF METALS. mould which come in contact with the mould now to be made, and then proceed to make the second mould in precisely the same manner as the first. When the second mould is hard, trim the edges and replace it upon the model ; the same pro- cess being continued until the entire original model is repro- duced in moulds fitting well together. To prevent the finished moulds from falling off, and to retain them in a firm position upon the original model, they are tied with lead wire or secured with catches of brass wire or sheet. When the moulds of the larger portion of the model, for instance, one-half of a statue, are finished, the so-called case or shell is made, /'. e., the backs of all the moulds are coated with a layer of plaster of Paris which holds them together. This case is best made not too thin in order to attain a better resisting power. The entire model having been cast in the manner above described, and the moulds provided with the case, the whole is completely dried in an oven. The next operation is to make the plaster of Paris impervious to fluids, as otherwise by the moulds absorbing the acid copper bath, copper would be deposited in the pores of the plaster and the moulds be spoiled, while the copy would turn out rough instead of having the smooth exterior of the model. To render plaster of Paris and other porous substances impervious, they are saturated with wax or stearine or covered with a coat of varnish, the latter process being generally employed for large moulds. Apply a coat of thick linseed oil varnish to the face of the mould, and, after drying, repeat the process until the mould is thought to be sufficiently impervious. Rendering the mould impervious with wax or stearine is a better and more complete method. For this purpose cut a groove in the rim of the mould, place in the groove a brass wire and twist the ends, which must be long enough to hold the mould by. The mould, having been previously dried, is then dipped into a bath of wax or stearine kept at a temperature of from 180 to 212 F., and a number of air bubbles will escape from the mould to the surface. When the production of air bubbles is consider- GALVANOPLASTY (REPRODUCTION). 393 ably diminished, remove the mould from the bath, and lay it face up in a drying oven, whereby the melting wax in conse- quence of its gravity oozes down, and the face of the mould is freed from an excess of wax. Whenever possible, submerging the entire mould should be avoided and the operation be con- ducted as follows : Place the heated mould in a vat filled with melted wax or stearine, so that the face does not come in con- tact with the wax, but absorbs wax by capillarity from the back. The moulds thus coated with varnish or saturated with wax are now made conductive with black-lead, the operation being the same as that mentioned on p. 372. For many undercut or deep portions black-leading is, however, not sufficient, and re- course must be had to making the moulds conductive or metallizing them by the wet way. Metallization by the wet way. This method consists in the deposition of certain metallic salts upon the moulds and their reduction to metal or conversion to conductive sulphur combi- nations. The process in general use is as follows : Apply with a brush upon the mould a not too concentrated solution of nitrate of silver in a mixture of equal parts of distilled water and 90 per cent, alcohol. When the coat is dry expose it in a closed box to an atmosphere of sulphuretted hydrogen ; the latter converts the nitrate of silver into sulphide of silver, which is a good conductor of the current. For the production of the sulphuretted hydrogen, place in the box, which contains the mould to be metallized, a porcelain plate or dish filled with dilute sulphuric acid (i acid to 8 water), and add five or six pieces of iron pyrites the size of a hazel-nut. The develop- ment of the gas begins immediately, and the box should be closed with a well-fitting cover to prevent inhaling the poison- ous gas; if possible, the work should be done in the open air or under a well- drawing chimney. The formation of the layer of sulphide of silver requires but a few minutes, and if not many moulds have to be successively treated, the acid is poured off from the iron pyrites and clean water poured upon the latter so as not to cause useless development of gas. 394 ELECTRO-DEPOSITION OF METALS. It has also been recommended to decompose the silver salt by vapors of phosphorus and to convert it into phosphide of silver, a solution of phosphorus in bisulphide of carbon being used for the purpose. The layer of silver salt is moistened with the solution or exposed to its vapors. This method possesses, however, no advantage over the preceding, because, on the one hand, the phosphorous solution takes fire spontan- eously, and, on the other, the odor of the bisulphide of carbon is still more offensive than that of sulphuretted hydrogen. A somewhat modified method is given by Parkes as follows : Three solutions, A, B, C, are required. Solution A is prepared by dissolving 0.5 part of caoutchouc cut up in fine pieces in 10 parts of bisulphide of carbon and adding 4 parts of melted wax ; stir thoroughly, then add a solution of 5 parts of phosphorus in 60 of bisulphide of carbon together with 5 of oil of turpentine and 4 of pulverized asphalt ; then thoroughly shake this mix- ture, A. Solution B consists of 2 parts by weight of nitrate of silver in 600 of water; and solution C of 10 parts of chloride of gold in 600 of water. The mould to be metalized is first provided with wires and then brushed over with, or immersed in, solution A, and after draining off, dried. The dry mould is then poured over with the silver solution (B) and suspended free for a few minutes until the surface shows a dark lustre. It is then rinsed in water and treated in the same manner with the chloride of gold solution (C), whereby it acquires a yellowish tone, when, after drying, it is sufficiently prepared for the re- ception of the deposit. Care must be taken in preparing solu- tion A, as the bisulphide of carbon containing phosphorus readily takes fire. Another method is as follows : Dissolve 5 parts by weight of wax in 5 of warm oil of turpentine, and add to the solution a mixture of 5 parts by weight of phosphorus, I of gutta-percha, 5 of asphalt in 120 of bisulphide of carbon. When both are thoroughly mixed, add to the whole a solution of 4 parts by weight of gun cotton in 60 of alcohol and 60 of ether, and after thoroughly shaking allow to settle. The next day pour off the GALVANOPLASTY (REPRODUCTION). 395 clear solution from the sediment, when the solution can at once be used. It is' especially well adapted for coppering parts of plants, leaves, flowers, etc. Another method of metallization is as follows : Immerse the leaves, etc., in iodized collodion composed of 40 per cent, alcohol 40 cubic centimeters, ether 60 cubic centimeters, potas- sium iodide I gramme, gun cotton I gramme. Allow the leaves, etc., to dry so that a firmly adhering layer is formed. Then immerse them in a solution of 10 parts by weight of nitrate of silver in 100 of water, whereby a layer of iodide of silver is formed. Now expose the article thus treated for some time to the light, and then immerse it in the reduc- ing fluid consisting of water 500 parts by weight, green vitriol 25, and acetic acid of 1.04, specific gravity 25. The reduction of silver now progresses rapidly and the articles are ready for coppering. In employing this process it must not be forgotten that the layer of collodion will not stand rough usage and, hence, injury to it by touching with the hands and careless placing of the conducting wire have to be avoided. By operating with due care, the results are very satisfactory and sure. Instead of the iodized collodion, a mixture of equal parts of white of egg and saturated solution of common salt may be used, the remainder of the process being the same as above described. Metallization by metallic powders. In some cases metalliza- tion by metallic powders is to be preferred to black- leading or metallizing by the wet way. Metallic or bronze powders are metals in a state of exceedingly fine powder of which, for galvanoplastic purposes, pure copper and brass powders only are of interest. Since such metallic powders adhere badly to waxed surfaces, the mould must be provided with a well-drying coat of lacquer, upon which, before it is completely dry, the powder is scattered or sifted. When the lacquer is hard a smooth surface is produced by going over the mould with a soft brush dipped in the metallic powder, an excess being re- moved by a thin jet of water. 396 ELECTRO-DEPOSITION OF METALS. Lcnoir's process Galvanoplastic method for originals in high relief. Lenoir's method for reproducing statues in a manner approaches in principle to that of the foundry. He begins by making with gutta-percha a mould in several pieces, which are united together so as to form a perfect hollow mould of the original. This having been done, cover all the parts carefully with black-lead. Make a skeleton with platinum wire, follow- ing the general outline of the model, but smaller than the mould, since it must be suspended in it without any point of contact. If the skeleton thus prepared is enclosed in the metallized gutta-percha mould, and the whole immersed in the galvanoplastic bath, it will be sufficient to connect the inner surface of the mould with the negative pole of the battery, and the skeleton of platinum wires (which should have no points of contact with the metallized surface of the mould) with the positive pole, in order to decompose the solution of sulphate of copper which fills the mould. When the metallic deposit has reached the proper thickness, the gutta-percha mould is removed by any convenient process, and a faithful copy of the original will be reproduced. Lead wires may be substituted for the expensive platinum wires. This method requires a knowledge of the moulder's art, so that good results can only be obtained by an experienced hand. Gelatine moulds. Under certain conditions the elasticity of gelatine allows of the possibility of its removal from undercut or highly-wrought portions of the model, when it reassumes the shape and position it had before removal therefrom. But gelatine requires that the deposit shall be made rapidly, other- wise it will swell and be partially dissolved by too long an im- mersion in the copper bath. To make a good gelatine mould proceed as follows : Allow white gelatine (cabinet-maker's glue) to swell for about 24 hours in cold water, then drain off the water, and heat the swollen mass in a water bath until completely dissolved. Compound the glue solution with pure glycerine in the pro- portion of 5 to 10 cubic centimetres (0.24 to 0.3 cubic inch) GALVANOPLASTY (REPRODUCTION). 397 of glycerine to 30 grammes (1.05 ozs.) of gelatine, which prevents the gelatine from shrinking in cooling. When some- what cooled off, apply the gelatine to the oiled original, which must be surrounded with a rim of plaster of Paris or wax, to prevent the gelatine from running off; when cold lift the gela- tine mould from the model. Before metallizing and suspend- ing in the copper bath, the mould has to be prepared to resist the action of the latter, as otherwise it would at once swell and be partially dissolved before being covered with the deposit. This is effected by placing the mould in a highly concentrated solution of tannin, which possesses the property of making gelatine insoluble. Brandley gives the following directions for preparing gelatine solution with an addition of tannin, which renders the moulds impervious to water : Dissolve 20 parts of the best gelatine in 100 of hot water, add j part of tannic acid and the same quan- tity of rock candy, then mix the whole thoroughly, and pour it upon the model. The same end is reached by making a mould with gelatine alone, then pouring an aqueous solution of 10 per cent, of bichromate of potassium upon it, and, after draining, exposing the mould to the action of the sun. Another method is as follows : Beat into a quart of distilled water the whites of two eggs, filter, and cover with this liquid the entire surface of the gelatine mould. After drying, operate with the solution of bichromate of potassium as in the preced- ing. By the solar action the coating impregnated with bichro- mate is rendered insoluble. The mould must finally be metallized and, when in the bath, submitted to a strong current at the beginning. When the entire surface is covered with the copper deposit, and when swelling is no longer to be feared, a weaker current may be used. In the following a few special uses of galvanoplasty will be briefly described : Nature printing, so named by Mr. v. Auer, Director of the 39 8 ELECTRO-DEPOSITION OF METALS. Imperial Printing Office at Vienna, has for its object the gal- vanoplastic reproduction of leaves and other similar bodies. The leaf is placed between two plates, one of polished steel, the other of soft lead, and is then passed between rollers, which exert a considerable pressure. The leaf thus imparts an exact impression of itself and of all its veins and markings to the lead, and this impression may be electrotyped, and the copper plate produced used for printing in the ordinary way. Instead of taking the impression in lead, it is advisable to use gutta-percha or wax for delicate objects, which should previously be black- leaded or oiled. In the same manner galvanoplastic copies of laces, etc., may be obtained. The process used by Philipp for coating laces and tissues with copper and then silvering or gilding, belongs rather to electro- plating than to galvanoplasty. The tissue is saturated with melted wax, and after removing the excess with blotting paper it is made conductive by black-leading with a brush. It is however preferable to metallize such delicate objects by the wet way, Parke's method being especially suitable for the purpose, and also a treatment with weak solution of nitrate of silver and pyrogallic acid frequently alternated. Corvin s niello. Corvin has invented a process of producing inlaid work by galvanoplasty, which has been patented, and is the exclusive property of J. P. Kayser & Son, of Crefeld. The process is as follows: A matrice of metal whose surface is finely polished is first made. This matrice may be used for the production of numerous duplicates of the same kind of object. The incrustations (mother-of-pearl, glass, ivory, amber, etc.) are then shaped by means of a saw, files, and other tools to the form corresponding to that which they are to occupy in the design. The side of the incrustation which is laid upon the matrice is, as a rule, smooth. The shaped incrustations, smooth side down, are pasted on to the parts of the model they are to occupy in the design. The latter being thus produced, the backs of the non-metallic laminae are metallized, and the por- tions of the metallic plate left free are slightly oiled. By now GALVANOPLASTY (REPRODUCTION). 399 placing the matrice thus prepared in the galvanoplastic bath, the copper is deposited not only upon the metallic matrice, but also upon the back of the inlaid pieces, the latter being firmly inclosed by the deposited metal. When the deposited metal has acquired the desired thickness it is detached from' the matrice, and incrustations with the right side polished are thus obtained. The laminae are more accurately and evenly laid in than would be possible by the most skilled hand-work. Grasses, leaves, flowers, etc., may be coated with copper and then silvered, gilded, or platinized, by first drying them, and, after giving them a certain elasticity by placing in glycerine, metallizing them by Parkes's or some other method. Plates for the production of imitations of leather are now fre- quently prepared. The demand for alligator and similar leathers is at the present time greater than the supply, and, therefore, imitations are made by pressing ox-leather, the plate being prepared by galvanoplasty, as follows : A large piece of the natural skin or leather is made impervious to the bath by repeated coatings with lacquer, and, when completely dry, secured with asphalt lacquer to a copper or brass plate. The leather is then black-leaded and, after being made conductive by copper wire or small lead plates, brought into the copper bath. When the copper deposit has acquired the desired thickness, the plate is further strengthened by backing with stereotype metal. To coat wood, etc., with a galvanoplastic deposit of copper. The absolutely dry objects are first immersed in melted wax, paraffine, or ceresine, and when thoroughly impregnated taken out and, after draining off, allowed to cool. As the impregnat- ing material contracts in cooling, the surface of the object is thereby freed from an excess of it. For this reason the ma- terial used for impregnating should not be made hotter than absolutely necessary, because the hotter it is the stronger the contraction or shrinkage. However, as by this contraction the edges and portions of the surface may become denuded of im- pregnating material, and thus be liable to be attacked by the 400 ELECTRO-DEPOSITION OF METALS. acid copper bath, it is advisable to coat the objects, after cool- ing, with an acid-resisting gutta-percha lacquer prepared by dissolving 5 to 10 parts, by weight, of gutta-percha cuttings in a mixture of 50 parts each of benzine and chloroform. Keep the solution in a wide-mouthed glass bottle provided with a well-fitting cork, and apply it with a brush. The solution being very inflammable, it should not be used near an open flame. Wooden handles of surgical instruments, etc., may be pro- tected from the attacks of the acid copper bath by coating them with a solution of wax or paraffine in ether, the latter after evaporating leaving a thin layer of wax upon the object. The articles thus prepared are black- leaded or metallized by Parkes's or one of the methods previously given, and brought into the copper bath. The mercury vessels of thermometers for vacuum and distilling apparatus are surrounded by a thick copper deposit to protect them from injury by mechanical force. The metallization of glass, porcelain, clay, terra-cotta, etc., is effected in the same manner as above described. Galvanoplastic operations in iron. Under " Deposition of iron," page 341, the galvanoplastic production of heavy de- posits of iron has already been referred to, it being there, also, mentioned that according to the researches of various authors a neutral solution of i^ ozs. of ammonio- ferrous sulphate in I quart of water is best adapted for the purpose, whilst Klein recommends a solution of equal parts of ferrous sulphate and sulphate of magnesia. To obtain any way successfully an iron electrotype from an original, for instance, from a copper plate, which should previously be oiled and then coated by means of sulphuretted hydrogen with a thin layer of sulphide of silver, the following conditions have to be fulfilled : The bath must be kept absolutely neutral according to one of the methods given on page 342, under formulae III. and IV. Further, the current-strength must be so regulated that absolutely no evolu- tion of gas on the object is perceptible, and the distance of the GALVANOPLASTY (REPRODUCTION). 40 1 anodes from the objects, which in the beginning of the opera- tion may be I ^ inches, must, according to Stammer, be grad- ually decreased to 0.19 inch. Furthermore, in the beginning of the operation the plates must at least every half hour be taken from the bath and rinsed off with a strong jet of water to remove adhering bubbles, the same object being attained by others by brushing the plates over with a feather. While out of the bath the plates must not be allowed to dry, as the fresh layers would not adhere to the places which have become dry. Now, even by strictly fulfilling the above-mentioned conditions, a faultless electrotype will be obtained only in one case out of five, this fact being mentioned in order to prevent practical electro-platers from wasting time and labor upon this process, which has not yet been sufficiently investigated and worked out. However, the interesting conditions for the production of heavy iron deposits present a field of research and observation to those who need not 'follow galvanoplasty fora living. In making such researches it should be especially observed whether useful heavy deposits can be obtained from iron baths in motion. Galvanoplastic operations in nickel. Though by the electro- deposition of nickel, electrotypes are rendered fit for printing with metallic colors, which attack copper, and their power of resisting wear is increased, the latter advantage can to the full- est extent be obtained only by a thick deposit. However, this always alters the design somewhat, especially the fine hatchings, this being the reason why in electro-nickeling electrotypes a deposit of medium thickness is, as a rule, not exceeded. If a hard nickel surface is desired, without injury to the fine lines of the design, the layer of nickel has to be reproduced by galvano- plasty, and the deposit of nickel strengthened in the copper bath. But upon black-leaded gutta-percha or wax moulds a nickel deposit can only be obtained in fresh baths ; the deposit, how- ever, is faultless only in rare cases, it generally showing holes in the depressions. Hence the object^has to be attained in a 26 402 ELECTRO-DEPOSITION OF METALS. round-about way, the mode of procedure being as follows : An impression of the original is taken in gutta-percha or wax, and from this impression a positive cliche in copper is made. The latter is then silvered, the silvering iodized as previously described, and a negative in copper is then prepared from this positive. The negative is again silvered, iodized, and then brought into a nickel bath where it receives a deposit of the thickness of stout writing-paper ; it is then rinsed in water, and the deposit immediately strengthened in the acid copper bath ; for the rest it is treated like ordinary copper deposits. Nickel electrotypes thus made are almost indestructible. Galvanoplaslic operations in silver and gold. The prepara- tion of reproductions in silver and gold also presents many difficulties. While copper is separable in a compact state from its sulphate solution, silver and gold have to be reduced from their double salt solutions potassium silver cyanide and potassium auric cyanide. However,' these alkaline solutions attack moulds of fatty substances, such as wax and stearine, consequently also plaster-of-Paris moulds impregnated with these substances, as well as gutta-percha and gelatine. Hence, only metallic moulds can be advantageously used except the end is to be attained in a roundabout way ; that is, by first coating the mould with a thin film of copper, strengthening this in the silver or gold bath and finally dissolving the film of copper with very 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 repro- duction in gold or silver of surfaces not in high relief or 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. Gal- vanoplastic reproductions in the noble metals are so seldom made in practice that it is not necessary to give further details. The composition of the baths generally used is as follows : COLORING, PATINIZING, OXIDIZING, LACQUERING. 40.3 Bath for galvanoplastic operations with silver. Fine silver (in the form of silver cyanide or chloride of silver) i ^ ozs., 98 per cent, potassium cyanide 5^ ozs., water I quart. Bath for galvanoplastic operations with gold. Fine gold (in the form of neutral chloride of gold) I oz., potassium cyanide ozs., water I quart. CHAPTER XV. COLORING, PATINIZING, OXIDIZING, ETC., OF METALS. LACQUERING. THOUGH, strictly speaking, these operations do not form a part of a work on the electro-deposition of metals, they re- quire to be mentioned, since the operator is frequently forced to make use of one or the other method in order to furnish basis-metals or electro-deposits in certain shades of colors ordered. By patina is understood the beautiful green color antique statues and other art-works of bronze acquire by long exposure to the action of the oxygen, carbonic aeid, and moisture of the air, whereby a thin layer of copper carbonate is formed upon them. It has been sought to accelerate by chemical means the formation of the patina thus slowly produced by the influence of time, and the term patinizing has been applied to this arti- ficial production of colors. Without drawing a strict line as to which processes have to be considered as coloring, and which as patinizing, the most approved methods for changing the color of the metals or of the deposits will be given. . i. Coloring of copper. All shades from the pale-red of cop- per to a dark chestnut-brown can be obtained by superficial oxidation of the copper. For small objects it suffices to heat them uniformly over an alcohol flame; with larger objects a more uniform result is obtained by heating them in oxidizing 404 ELECTRO-DEPOSITION OF METALS. 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 I part of black-lead, or i part each of ferric oxide and black-lead, with alcohol or water. Apply the paste as uni- formly as possible with a brush and place the object in a warm place (oven or drying chamber). The darker the color is to be the higher the temperature must be, and the longer it must act upon the object. When sufficiently heated the dry powder is removed by brushing with a soft brush, and the manipulation repeated if the object does not show a sufficiently dark tone. Finally the object is rubbed with a soft linen rag moistened with alcohol, or brushed with a soft brush and a few drops of alcohol until completely dry, and then with a brush previously rubbed upon pure wax. The more or less dark shade pro- duced in this manner is very warm and resists the action of the air. Brown color upon copper is obtained by applying to the thoroughly cleansed surface of the object a paste of verdigris 3 parts, ferric oxide 3, sal ammoniac I, and sufficient vinegar, and heating until the applied mixture turns black ; the object is then washed and dried. By the addition of some blue vitriol the color may be darkened to chestnut-brown. A brown color is also obtained by brushing to dryness with a hot solution of I part of potassium nitrate, I of common salt, 2 of ammonium chloride, and I of liquid ammonia in 95 of vinegar. A warmer tone is, however, produced by the method introduced in the Paris Mint, which is as follows : Powder and mix intimately equal parts of verdigris and sal ammoniac. Take a heaping tablespoonful of this mixture and boil it with water in. a copper kettle for about twenty minutes and then pour off the clear fluid. To give copper objects a bronze-like color with this fluid, pour part of it into a copper pan ; place the objects separately in it upon pieces of wood or glass, so that they do not touch each other, or come in contact with the copper pan, and then boil them in the liquid for a quarter of COLORING, PATINIZING, OXIDIZING, LACQUERING. 405 an hour. Then take the objects from the solution, rub them dry with a linen cloth, and brush them with a waxed brush. A red-brown color on copper is produced in China by the application of a paste of verdigris 2 parts, cinnabar 2, sal ammoniac 5, and alum 5, with sufficient vinegar, heating over a coal fire, washing and repeating the process. 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 mix- ture is allowed to act for a greater length of time the tone is changed and several different shades of great beauty are obtained. After rinsing, dry in hot saw-dust and lacquer with colorless spirit lacquer. Copper is colored blue-black by dipping the object in a hot solution of \\y drachms of liver of sulphur in I quart of water, moving it constantly. Bhie-gray shades are obtained with more dilute solutions. It is difficult to give definite di- rections as to the length of time the solution should be allowed to act, since this depends on its temperature and concentra- tion. With some experience the correct treatment, however, will soon be learned. The so-called cuivre fume is produced by coloring the copper or coppered objects blue-black with solution of liver of sulphur, then rinsing, and finally scratch-brushing them, whereby the shade becomes somewhat lighter. From raised portions which are not to be dark, but are to show the color of copper, the coloration is removed by polishing upon a felt wheel or bob. Black color upon copper is produced by a heated pickle of 2 parts of arsenious acid, 4 of concentrated muriatic acid, I of sulphuric acid of 66 Be., and 24 of water. Dead-black on copper. Brush the object over with a solution of i part of platinum chloride in 5 of water, or dip it in the 406 ELECTRO-DEPOSITION OF METALS. solution. A similar result 4s obtained by dipping the copper object in a solution of nitrate of copper or of manganese, and drying over a coal fire. These manipulations are to be repeated until the formation of a uniform dead-black. The following solution is recommended for obtaining a deep black color on copper and its alloys: 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 solution about three times more dilute than the above, viz. : Copper 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, to heat the work on a hot plate until the copper salt is decom- posed into the black copper oxide. It would be difficult to heat large articles upon a hot plate, but a closed muffle furnace should give better results than an open coal fire. In any case the heating process should not be continued longer than neces- sary to produce the change mentioned above. Imitation of genuine patina. Repeatedly brush the objects with solution of sal ammoniac in vinegar; the action of the solution being accelerated by the addition of verdigris. A solution of 9 drachms of sal ammoniac and 2^ drachms of potassium binoxalate in I quart of vinegar acts still better. When the first coating is dry, wash the obfect, and repeat the manipulations, drying and washing after each application, until a green patina is formed. It is best to bring the articles after being brushed over with the solution into a hermetically closed box, upon the bottom of which a few shallow dishes containing very dilute sulphuric or acetic acid and a few pieces of marble are placed. Carbonic acid being thereby evolved and the air in the box being kept sufficiently moist by the evaporation of COLORING, PATINIZING, OXIDIZING, LACQUERING. 407 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 object with a solution of 4^ ozs. of ammonium carbonate and I J^ ozs. of sal ammoniac in I quart of water, to which a small quantity of gum tragacanth may be added. To produce a steel-gray color upon copper immerse the clean and pickled objects in a heated solution of chloride of antimony in hydrochloric acid. By using a strong electric current the objects may alsp be coated with a steel-gray deposit of arsenic in a heated arsenic bath. For coloring copper dark steel-gray, a pickle consisting of I quart of hydrochloric acid, 0.125 quart of nitric acid, \y 2 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 IOO parts, hydrochloric acid i j, and lampblack y. Then dissolve in a quart of water ^/^ ozs. of sodium hyposulphite, and in another quart of water 14^ drachms of blue vitriol, 5^ drachms of crystallized verdigris, and 7^ grains of sodium arsenate. Mix equal volumes of the two solutions, but no more than is actually necessary for the work in hand, and heat to between 167 and 176 F. By dipping articles of copper, brass, or nickel in the hot solution they become immediately colored with the colors mentioned below, one color passing within a few seconds into the other, and for this reason the effect must be constantly controlled by frequently taking the objects from the bath. The colors successively formed are as follows : Upon copper : Upon brass : Upon nickel : Orange, Golden-yellow, Yellow, Terra-cotta, Lemon color, Blue, Red (pale), * Orange, Iridescent. Blood-red, Terra-cotta, Iridescent. Olive-green. 408 ELECTRO-DEPOSITION OF METALS. Some of these colors not being very durable, have to be pro- tected by a eoat 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 of brass and bronzes. Most of the directions given for coloring copper are also available for brass and bronzes, especially those for the production of the green patina, and the oxidized tones by a mixture of ferric oxide and black- lead. Many colorations on brass, however, are effected only with difficulty, and are partially or entirely unsuccessful, as, for in- stance, coloring black with liver of sulphur. As a pickle for the production of a Lustrous black on brass, the following solution may be used : Dissolve freshly precipitated carbonate of copper, while still moist, in strong liquid ammonia, using sufficient of the copper salt so that a small excess remains undissolved, or, in other words, that the ammonia is saturated with copper. The car- bonate of copper is prepared by mixing hot solutions of equal parts of blue vitriol and of soda, filtering off", and washing the precipitate. Dilute the solution of the copper salt in ammonia with one- fourth its volume of water, add 31 to 46 grains of black-lead, and heat to between Q5 and 104 F. Place the clean and pickled objects in this pickle for a few minutes, until they show a full black shade, then rinse in water, dip in hot water and dry in sawdust. The solution soon spoils, and hence no more than required for immediate use should be prepared. Another method of coloring brass black has been given under " Deposition of Arsenic," p. 346. Urquhart states that clean brass and copper may be covered with a firmly adherent black coating by placing them very near to the flames of burning straw. . It will not rub off", and may be polished with a soft cloth. S'teel-gray on brass is obtained by the use of a mixture of I COLORING, PATINIZING, OXIDIZING, LACQUERING. 409 lb. of strong hydrochloric acid with I pint of water, to which are added 5*^ ozs. of iron filings and a like quantity of pul- verized antimonic sulphide. Hydrochloric acid compounded with arsenious acid is also recommended for this purpose. The mixture is brought into a lead vessel, and the objects dipped in it should come in contact with the lead of the vessel, or be wrapped around with a strip of lead. A gray color with a bluish tint upon brass is produced with solution of antimonious chloride (butter of antimony), while a pure steel-gray color is obtained with a hot solution of arsenious chloride with a little water. A pale gold color on brass is obtained in the following bath : Dissolve in 90 parts by weight of water, 3.6 parts by weight of caustic soda and the same quantity of milk sugar. Boil the solution y hour. Then add a solution of copper vitriol 3.6 parts by weight in 10 of hot water and use the bath at a tem- perature of 176 F. Straw color, to brown, through golden yellow, and tombac color on brass may be obtained with solution of carbonate of copper in caustic soda lye. Dissolve 5^5 ozs. of caustic soda in I quart of water, and add I ^ 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 lustre ; with the hot solution the coloration is more rapidly effected. A color resembling gold or brass is, according to Dr. Kayser, obtained as follows: Dissolve 8^ drachms of sodium hypo- sulphite in 17 drachms of water, and add 5.64 drachms of solution of antimonious chloride. 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, sus- pend it in 2 or 3 quarts of hot water ; then heat and add con- centrated 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 colo- 410 ELECTRO-DEPOSITION OF METALS. ration. The articles become gray by regaining too long in the bath. Broivn color, called bronze Ba'rbcdienne, on brass. This beau- tiful color may be produced as follows : Dissolve by vigorous shaking in a bottle, freshly prepared arsenious sulphide in spirit of sal ammoniac, and compound the solution with antimonious sulphide until a slight permanent turbidity shows itself, and the fluid has acquired a deep yellow color. Heat the solution to 95 F., and suspend the brass objects in it. They become at first golden-yellow and then brown, but as they come from the bath with a dark dirty tone, they have to be several times scratch-brushed to bring out the color. If, after using it several times, the solution fails to work satisfactorily, add some anti- monious sulphide. The solution decomposes rapidly, and should be prepared fresh every time it is to be used. 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 aurantianum} with I part of finely pulverized bloodstone, and triturate the mixture with ammonium sulphide to a not too thickly-fluid pigment. Apply this pigment to the objects with a brush, and, after allowing it 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 thor- oughly rinsed objects with dilute antimony bisulphide, and, after drying, removing the coating of separated sulphur by brushing. Dilute solution of sulphide of arsenic in ammonia is then applied, 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. COLORING, PATINIZING, OXIDIZING, LACQUERING. 41! Smoke-bronze. Bronzing with smoke is sometimes resorted to in order to give the metal an ancient appearance. This is effected by exposing the work to the smoke of a fire for some days, when it receives a firm coating of a dark color. The articles are generally suspended over the smoky fire of a furnace by means of brass wire. When 'the furnace is suffi- ciently heated the smoke is maintained by burning hay and other substances which produce copious smoke with the coal. When the right tint is attained the articles are removed from the furnace and allowed to cool without touching them with the hands. The hotter the articles have been made the darker will be the color. If the articles which have been smoked have been previously coated with a green bronze, then it is well to finish with a waxed brush. Violet- and corn-flower blue upon brass may be produced as follows: Dissolve in I quart of water 4^ ozs. of sodium hypo- sulphite, and in another quart of water I oz. 3^ drachms of crystallized sugar of lead, and mix the solutions. Heat the mixture to 176 F., and then immerse the 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 the brass objects and produces the various lustrous colors. Similar lustrous colors are obtained by dissolving 2.11 ozs. of pulverized tartar in I quart of water, and I oz. of chloride of tin in y 2 pint of water, mixing the solution, heating, and pour- ing the clear mixture into a solution of 6.34 ozs. of sodium hyposulphite in I pint of water. Heat this mixture to 176 F., and immerse the pickled brass objects. Ebermayer* s experiments in coloring brass. In the following the results of Ebermayer's experiments are given, In testing the directions, the same results as those claimed by Ebermayer were not always obtained ; and variations are given in paren- theses. 412 ELECTRO-DEPOSITION OF METALS. I. Blue vitriol 8 parts by weight, crystallized sal ammoniac 2, water 100, give by boiling a greenish color. (The color is olive-green, and useful for many purposes. The coloration however succeeds only upon massive brass, but not upon brassed zinc.) II. Potassium chlorate 10 parts by weight, blue vitriol 10, water 1000, given by boiling a brown-orange to cinnamon-brown color. (Only a yellow-orange color could be obtained.) III. By dissolving 8 parts by weight of blue vitriol in 1000 of water, and adding 100 of caustic soda until a precipitate is formed, and boiling the objects in the solution, a gray-brown color is obtained, which can be made darker by the addition o* colcothar. (Stains are readily formed. Brassed zinc acquires a pleasant pale-brown.) IV. With 50 parts by weight of caustic soda, 50 of sulphide of antimony, and 500 of water, a pale fig-brown color is pro- duced. (Fig-brown could not be obtained, the shade being rather dark olive-green.) V. By boiling 400 parts by weight of water, 25 of sulphide of antimony, and 60 of calcined soda, and filtering the hot solu- tion, mineral kermes is precipitated. By taking of this 5 parts by weight and heating with 5 of tartar, 400 of water, and 10 of sodium hyposulphite, a beautiful steel-gray is obtained. (The result is tolerably sure and good.) VI. Water 400 parts by weight, potassium chlorate 20, nickel sulphide 10, give after boiling for some time a 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 brown-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 obtained. The formula, however, is not available for brassed zinc.) COLORING, PATINIZING, OXIDIZING, LACQUERING. 413 3. Coloring zinc. The results obtained by coloring zinc directly according to existing directions cannot be relied on, and it is, therefore, recommended to first copper the zinc and then color the coppering. Experiments in coloring zinc black with alcoholic solution of chloride of antimony according to Dullas's process gave no useful results. Puscher's method is better ; according to it the objects are dipped in a boiling solution of 5.64 ozs. of pure green vitriol and 3.17 ozs. of sal ammoniac in 2^/ 2 quarts of water. The loose black precipitate deposited upon the objects is removed by brushing, the object again dipped in the hot solution and then held over a coal fire until the sal ammoniac evaporates. By repeating the opera- tion three or four times a firmly adhering black coating is formed. To color zinc black with nitrate of manganese, as proposed by Neumann, is a tedious operation, it requiring to be repeated seven or eight times. It is done by dipping the object in a solution of nitrate of manganese and heating over a coal fire, the manipulations being repeated until a uniform dead-black is obtained. 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 attained 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 sal ammoniac in I quart of water. The articles become first dark yellow, then, successively, brown, purple-violet, and indigo-blue, and stand slight scratch-brushing and polishing. A gray coating on zinc is obtained by a deposit of arsenic in a heated bath composed of 2.82 ozs. of arsenious acid, 8.46 drachms of sodium pyrophosphate, and I ^ drachms of 98 per cent, potassium cyanide and I 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 414 ELECTRO-DEPOSITION OF METALS. paste of pipe-clay to which has been added a solution of I part by weight of crystallized verdigris, I of tartar, and 2 of crystal- lized soda. Kletzinski states that a solution of molybdic acid, or ammo- nium molybdate, in nitric acid, made very dilute, furnishes a good liquid for producing a brown patina on cast zinc. The object assumes iridescent colors on immersion which he con- siders to be due to molybdenum oxide The following pro- portions were tried with the following results : Ammonium molybdate 1,550 grains, ammonia 2,325 grains, water I pint. Zinc acquired a beautiful iridescent appearance after a few moments' immersion in the solution. On continuing the pro- cess, the iridescent colors were succeeded by a light yellowish- brown color, and this, on warming the solution, was followed by a slaty-black, which was more opaque than any of the pre- ceding colors. Brass and tin are unaffected when immersed alone, but tin when placed in contact with zinc assumes a beautiful dark violet color, which is firmly adherent to the metal. Iron in contact with tin is simply stained. Red-brown color on zinc. Rub with solution of chloride of copper in liquid ammonia. Yellow-brown shades on zinc. Rub with solution of chloride of copper in vinegar. 4. Coloring of iron. The browning of gun-barrels is effected by the application of a mixture of equal parts of butter of anti- mony and olive oil. Allow the mixture to act for 12 to 14 hours, then remove the excess with a woollen 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 lustrous black on iron is obtained by the application of solution of sulphur in spirits of turpentine prepared by boiling upon the water bath. After the evaporation of the spirits of COLORING, PATINIZING, OXIDIZING, LACQUERING. 415 turpentine a thin layer of sulphur remains upon the iron, which, on heating the object, immediately combines with the metal. By another method the cleansed and pickled iron objects are coated, when dry, with linseed oil, and heated to a dark red. If pickling is omitted, the coating with linseed oil and heating may have to be repeated two or three times. 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 a cathode. The method was tested as follows : A piece of bright sheet pen-steel was placed in distilled water and made the anode by connecting with the positive pole of a plating dynamc, 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 wanting in uniformity. The experi- ment was repeated with larger plates, when a good blue-black color was obtained on the anode in half an hour. On drying out 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 back of the anode. The water became of a yellowish color. Fresh distilled water was then boiled for a long time so as to expel all trace of the 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 interval of one hour a slight darkening occurred, but the effect 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 con- dition, and gradually unites with the iron. The dead black coating on clock cases of iron and steel is not produced by the galvanic process. 416 ELECTRO-DEPOSITION OF METALS. According to Bottger a durable blue on iron and steel may be obtained by dipping the article in a ^ per cent, solution of red prussiate of potash mixed with an equal volume of a ^ per cent, ferric chloride solution. A brown-black coating with bronze lustre on iron is obtained by heating the bright iron objects and brushing them over with concentrated solution of potassium bichromate. 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 I part of sal ammoniac in water. To give iron a silvery appearance with high lustre. Scour the polished and pickled iron objects with a solution prepared as follows : Heat moderately I y 2 ozs. of chloride of antimony, 0.35 oz. of pulverized arsenious acid, 2.82 ozs. of elutriated bloodstone with I quart of 90 per cent, alcohol upon a water bath for half an hour. Partial solution takes place. Dip into this fluid a tuft of cotton and go over the iron portions, using slight pressure. A thin film of arsenic and antimony is thereby deposited, which is the more lustrous the more carefully the iron has been previously polished. 5. Coloring of tin. A bronze-like patina on tin may be ob- tained by brushing the object over with a solution of I ^ ozs. of blue vitriol and a like quantity of green vitriol in I quart of water, and moistening the object when dry with a solution of 3^ ozs. of verdigris in 10^ ozs. of vinegar. When dry, polish the object with a soft waxed brush and some ferric oxide. The coating thus obtained being not especially durable, must be protected by a coating of lacquer. Durable and very warm sepia-brown tone upon tin and its alloys. Brush the object over with a solution of I 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 lustre appears. A dark coloration is also obtained with ferric chloride solution. COLORING, PATINIZING, OXIDIZING, LACQUERING. 417 6. Coloring of silver. See " Silvering," p. 282. 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 by means of a fine flat fitch-brush, the object having previously been heated hand-warm. After lacquering, the object is dried in an oven at a temperature of between 140 and 158 F., whereby small irregularities are ad- justed, and the layer of lacquer becomes transparent, clear, and lustrous. Cellulose lacquers and varnishes. Under the name of zapon a dip-lacquer has been introduced in commerce. It represents a clear, almost colorless fluid of the consistency of collodion, and smells something like fruit ether. According to G. Buch- ner, it consists essentially of a solution of cellulose in a mixture of amyl acetate and acetone. Of the last two bodies, the "thinning fluid," which accompanies the preparation, also con- sists. This lacquer can be highly recommended, its superiority being due to the favorable properties of the cellulose. The transparent, colorless coat obtained with zapon can be bent with the metallic sheet, to which it has been applied, without crack- ing. It is so hard that it can scarcely be scratched with the finger-nail, shows no trace of stickiness, and it is perfectly homogeneous 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 advantage of zapon especially as regards metallic objects is that the coating, in consequence of its physical con- 27 41 8 ELECTRO-DEPOSITION OF METALS. stitution, preserves the character of the basis. In accordance with the nature of cellulose, 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 conse- quence of the loss of molecular coherence. It can be washed with soap and water, and protects metals coated with it from the action of the atmosphere. Zapon may also be colored, but, of course, only with coloring substances mostly aniline colors which are soluble in the solvent used for the cellulose. A similar preparation is known as kristaline. It is a hard, transparent enamel, which can be applied as a lacquer in all kinds of metal-work without affecting the most delicate finish. It is applied by dipping, is invisible, and leaves no mark in drying. Kristaline has now been in use for about ten years, and can be relied upon to protect all metal-work from acids and alkalies, also coal-gas, alcohol, benzine, oil, water, fly-specks, etc. It is especially designed to prevent the highest class of metal-work from tarnishing and to preserve the delicate shades of color produced by electricity and artificial oxidation. A lacquer similar to zapon or kristaline may be prepared by substituting soluble pyroxylin for cellulose, the process being as follows : Bring collodion-cotton, i. e., soluble pyroxylin, such as is used by photographers, into a box which can be hermetic- ally closed, and place upon the bottom of the box a dish with sulphuric acid. The purpose of this is to dry the collodion- cotton, which requires from 36 to 48 hours. The collodion- cotton is then brought into a large bottle, and three to four times its quantity by weight of very strong alcohol poured over it. In a few days the greater portion of it is dissolved, when the clear solution is poured into another bottle. Add to the clear solution more collodion-cotton, about 25 to 30 per cent, of the weight of the quantity originally used, and the resulting product forms an excellent cellulose lacquer, which rapidly hardens to a perfectly transparent and very glossy coating. For diluting cellulose lacquers it is best to use wood spirit. To COLORING, PATINIZING, OXIDIZING, LACQUERING. 419 color them, dissolve an aniline color in strong spirits of wine, add a corresponding quantity of the solution to the lacquer, and shake vigorously. In conclusion, a few words may be said in regard to the pro- cesses by which those magnificent effects are obtained which imitate so completely the appearance, freshness, and rich tones of real gilding. In general, gold varnish is applied only upon copper and its more or less yellow alloys. Gold varnishers operate as follows : After the objects have been perfectly cleansed, scratch-brushed, and burnished, if necessary, they are completely dried in hot sawdust and wiped clean with a fine cloth. A light coat of varnish is then applied with a fitch-pencil, and all excess of varnish removed or leveled with another flat brush of badger-hair or bristles. The two brushes are kept together in the same hand, the varnish brush between the thumb and first two fingers, while the flat one (without a handle) is held between the other fingers and the palm of the hand. In this manner there is no interval in the use of the two brushes. The varnish is kept in a jelly-pot or other similar vessel, across the top of which a string has been stretched. This string is intended for removing by wiping the excess of varnish taken up by the brush or pencil. The varnish which covers the burnished parts of the object may be removed with a clean rag moistened with alcohol and wrapped round the finger. Another dry cloth finishes the drying. Sometimes the burnished parts are also varnished, but the operation is very difficult when their surface is considerable. Round-ware, pol- ished or burnished, may be varnished in the lathe. After the varnish has been applied as uniformly as possible, the objects are put in a drying stove heated to between 140 and 175 F. The alcohol or essential oils of the varnish are rapidly volatilized, while the resins or gums melt and cover the objects with a glassy lustre. The heat must be sufficient to melt these gums, but low enough to avoid burning them. When the operation has been well performed, the pieces pre- sent a beautiful and uniform golden appearance, with no disfig- 420 ELECTRO-DEPOSITION OF METALS. tiring red patches, which latter indicate an unequal thickness of varnish. Varnishers have always at their disposal four varnishes of different shades red gold, orange-yellow gold, green gold, and colorless varnish for mixture. This last is employed for dilut- ing the first three and diminishing the depth of their colors. Each of these various varnishes gives to copper the gold color peculiar to it, and, when mixed, intermediary shades. It often happens that the various parts of a large piece are different in composition and color, and the varnisher is obliged to impart the same shade of gold all over by skilful combinations of varnishes. He thus succeeds in giving the same gold color to half-red copper and to alloys of yellow and green brass. But a small quantity of varnish is poured into the varnish pot at one time, to prevent it from thickening by evaporation, and after the operation the residue is poured back into the flask from which it was taken and kept well stoppered. The brushes and pencils must be often washed in alcohol, which may afterwards be used for diluting thick varnishes. These varnishes are made by dissolving various resinous substances, like sandarac, benzoin, dragon's-blood, elemi, gamboge, etc., and tinctorial matters, such as saffron, annotto, alkanet, etc., in a mixture of alcohol with essence of lavender or of spikenard. All qualities of varnish are to be found, but the more expensive are often the more economical. To remove the varnish from an imperfectly varnished object or from an old one, it is immersed in alcohol or concentrated sulphuric acid, or, better still, in a boiling solution of caustic lye. The varnishing is then begun anew. HYGIENIC RULES FOR THE WORKSHOP. 421 CHAPTER XVI. HYGIENIC RULES FOR THE WORKSHOP. IN but few otherbranches of the industry has the workman so constantly to deal with powerful poisons, as well as other substances and vapors, which are exceedingly corrosive in their action upon the skin and the mucous membranes, as in electro-plating. However, with the necessary care and sobri- ety, all influences 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 neutralize the action of the acid upon the" enamel of the teeth and the mucous membrane of the mouth and throat by frequently rins- ing the mouth with dilute solution of bicarbonate of soda. Workmen engaged in freeing the objects from grease lose, for want of cleanliness, the skin on the portions of the fingers which come constantly in contact with the lime and caustic lyes. This may be 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 lime. It should be a rule for every workman employed in an electro-plating establishment not to drink from vessels used in electroplating manipulations ; for instance, porcelain dishes, beer glasses, etc. One workman may this moment use such a 422 ELECTRO-DEPOSITION OF METALS. vessel to drink from and without his knowledge another may employ it the next moment for dipping out potassium cyanide solution, and the first using it again as a drinking vessel may incur sickness or even fatal poisoning. The handling of potas- sium cyanide and its solutions requires constant care and judg- ment. Working with sore hands in such solutions should be avoided as much as possible ; but if it has to be done, and the workman feels a sharp pain in the sore, wash the latter quickly with clean water and apply a few drops of green vitriol solution. Many individuals are very sensitive to nickel solutions, erup- tions, 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 eruptions. In such case 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 nickel solution, as, for instance, in taking out with the hand an object fallen into a nickel bath. Below will be found some directions for neutralizing, in case of internal poisoning, the effects of the poison either entirely or at least sufficiently to retard its action until professional aid can be summoned. Poisoning by hydrocyanic (prussic) acid, potassium cyanide, or cyanides. If prussic acid, or the cyanides, be concentrated or have been absorbed in considerable quantity, their action is almost instantly fatal, and there is little hope of saving the victim, although everything possible should be tried. But if these substances have been taken in very dilute condition, they may not prove immediately fatal, and there is some hope that remedial measures may be successfully applied. In poisoning with these substances, water as cold as possible should be run upon the head and spine of the patient, and he should be made to inhale, carefully and moderately, the vapor of chlorine water, bleaching powder, or Javelle water (hypo- chlorite of soda). Should these poisons be introduced into the stomach, there HYGIENIC RULES FOR THE WORKSHOP. 423 should be administered as soon as possible the hydrate of sesquioxide of iron, or, what is better, dilute solutions of the acetate, citrate, or tartrate of iron. With proper precautions a very dilute solution of sulphate of zinc may be given. Poisoning by copper-salts. The stomach should be quickly emptied by means of an emetic or, in want of this, the patient should thrust his finger to the back of his throat and induce vomiting by tickling the uvula. After vomiting drink milk, white of egg, gum-water, or some mucilaginous decoction. Poisoning by lead-salts requires the same treatment as poisoning by copper-salts. Lemonade of sulphuric acid, or an alkaline 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 anti- dote. Calcined magnesia being generally on hand, mix it with 1 5 to 20 times the quantity of water and give of this mix- ture 3 to 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 administer a few spoonfuls of olive oil. Poisoning by mercury -salts. Mercury salts, and particularly the chloride (corrosive sublimate), form with the white of egg (albumen) a compound very insoluble and inert. The remedy, albumen, is therefore indicated. Sulphur and sulphuretted water are also serviceable for the purpose. Poisoning by sulphuretted hydrogen. The patient should be made to inhale the vapor of chlorine from chlorine water, Javelle water, or bleaching-powder. Energetic friction, espec- ially 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 424 ELECTRO-DEPOSITION OF METALS. gases. Admit immediately an abundance of fresh air, and ad- minister light inspirations of ammonia. Give plenty of hot drinks and excite friction, in order to conserve the warmth and transpiration of the skin. Employ hot foot-baths to remove the blood from the lungs. Afterwards maintain in the mouth of the patient some substance which, melting slowly, will keep the throat moist, such as jujube and marshmallow paste, molasses candy, and liquorice paste. Milk is excellent. CHAPTER XVII. CHEMICAL PRODUCTS AND VARIOUS APPARATUS AND INSTRUMENTS USED IN ELECTRO-PLATING. A. CHEMICAL PRODUCTS. BELOW the characteristic properties of the chemical pro- ducts 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. I. Sulphuric acid (oil of vitriol). Two varieties of this acid are found in commerce, viz., fuming sulphuric acid (disulphuric acid), and ordinary sulphuric acid. The first is a thick oily fluid generally colored yellowish by organic substances, and emits dense white vapors in the air. Its specific gravity is 1.87 to 1.89. The only purpose for which fuming sulphuric acid is used in the electro-plating art is as a mixture with nitric acid, for stripping silvered objects. Ordinary sulphuric acid has a specific gravity of 1.84. Diluted with water it serves for filling the Bunsen elements and as a pickle for iron; in a concentrated state it is used in the CHEMICAL PRODUCTS. 425 preparation of pickles and as an addition to the galvanoplastic copper bath. The crude commercial acid generally contains arsenic, hence care must be had to procure a pure article. In diluting the acid with water, it should in all cases be added to the water in a very gentle stream and with constant stirring, as otherwise a sudden generation of steam of explosive violence might result, and the dangerous corrosive liquid be scattered in all directions. Concentrated sulphuric acid vigorously attacks all organic substances, and hence has to be kept in bottles with glass stoppers, and bringing it in contact with the skin should be carefully avoided. Recognition. One part of acid mixed with 25 parts of dis- tilled water gives, when compounded with a few drops of bar- ium chloride solution, a white precipitate of barium sulphate. 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., being 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 characteristic odor, by which the concentrated acid is readily distinguished from other acids. It is used for filling the Bun- sen elements, and for pickling in combination with sulphuric acid and chlorine. On coming in contact with the skin it produces yellow stains. Recognition. By heating the not too dilute acid with copper, brown-red vapors are evolved. For the determination of dilute nitric acid, add a few drops of it to green vitriol solution, when a black-brown coloration will be produced on the point of con- tact. 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 distinguished from other acids. The specific gravity of the strongest hydro- chloric acid is 1.2; the crude acid of commerce has a yellow color, due to iron, and contains arsenic. Dilute hydrochloric acid is used for pickling iron and zinc. 426 ELECTRO-DEPOSITION OF METALS. Recognition. On adding to the acid strongly diluted with distilled water a few drops of solution of nitrate of silver in distilled water, a heavy white precipitate is formed, which be- comes 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 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 immersing 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 plat- inum baths. Recognition. Lime-water compounded with aqueous solution of citric acid remains clear in the cold, but on boiling deposits a precipitate of calcium citrate. This precipitate is soluble in ammonium chloride, but on boiling is again precipitated, and is then insoluble in sal ammoniac. 6. Boric acid (boracic acid}. This acid is found in com- merce in the shape of scales with nacreous lustre and greasy to the touch ; when obtained from solutions by evaporation, it forms colorless prisms. Its specific gravity is 1.435 ; it dissolves CHEMICAL PRODUCTS. 427 with difficulty in cold water (i part of acid requiring, at 64.4 F., 28 of water), but is more rapidly soluble in boiling water ( i part of acid requiring 3 of water at 212 F.) . According to Weston's proposition, boric acid is employed as an addition to nickel baths, etc. Recognition. By mixing solution of boric acid in water with some hydrochloric acid and dipping turmeric paper in the solu- tion, the latter acquires a brown color, the color becoming more intense on drying. Alkalies impart to turmeric paper a similar coloration, which, however, disappears on immersing the paper in dilute hydrochloric acid. 7. Arsenious acid (white arsenic, arsenic, ratsbane}. It gen- erally occurs in the shape of a white powder and sometimes in vitreous-like lumps, resembling porcelain ; for our purposes the white powder is almost exclusively used. It is slightly soluble in cold water, and more readily 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 some arsenious acid is thrown upon glowing coals an odor resembling that of garlic is perceptible. By mixing solution of arsenious acid, prepared by boiling with water, with a few drops of ammoniacal solution of nitrate of silver, a yellow precipitate of arsenate of silver is obtained. The ammoniacal solution of nitrate of silver is prepared by adding ammonia to solution of nitrate of silver until the pre- cipitate 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 428 ELECTRO-DEPOSITION OF METALS. strongly diluted solution of it gives, after neutralizing with caustic alkali and adding a few drops of nitrate of silver solu- tion, a crimson-red precipitate of chromate of silver. 9. Hydrofluoric acid. A colorless, corrosive, very mobile liquid of a sharp, pungent odor. The anhydrous acid fumes strongly in the air and attracts moisture with avidity. Hydro- fluoric acid is used for etching glass and for pickling aluminium dead white. Great care must be observed in working with the acid, since not only the aqueous solution, but also the vapors, have an extremely corrodent effect upon the skin and respira- tory organs. Recognition. By covering a small platinum dish containing hydrofluoric acid with a glass-plate free from grease, the latter in half an hour appears etched. II. Alkalies and Alkaline Earths. 10. Potassium hydrate {caustic potash}. It is found in com- merce in various degrees of purity, either in sticks or cakes. It is very deliquescent and dissolves readily in water and alco- hol ; by absorbing carbonic acid from the air it rapidly becomes converted into the carbonate and thus loses its caustic proper- ties. It should, therefore, be stored 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 be at once several times rinsed with water and then with very di- lute acetic acid. Pure caustic potash serves as an addition to zinc baths, gold baths, etc. For the purpose of freeing objects from grease the more impure commercial article is used. 11. Sodium hydrate {caustic soda}. It also occurs in com- merce in various degrees of purity, either in sticks or lumps. It is of a highly caustic character resembling potassium hy- drate (see above) in properties and effects. It is employed for freeing objects from grease. CHEMICAL PRODUCTS. 429 12. Ammonium hydrate (ammonia or spirits of hartshorn). It is simply water saturated with ammonia gas. By expos- ure ammonia gas is gradually evolved, so that it must be stored in closely-stoppered bottles in order to preserve the strength of the solution unimpaired. Four qualities are gen- erally found in commerce, viz., ammonia of 0.910 specific gravity (containing 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 percent, of ammonia gas); and 0.960 specific gravity (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, hydro sulphuric 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 on p. 393, where the manner of evolving it is also given. It is sometimes employed for the production of "oxidized" silver. Bringing not only metallic salts, but gilt or silvered articles, or pure gold and silver, in contact with sul- phuretted hydrogen, should be carefully avoided, they being rapidly sulphurized by it. 430 ELECTRO-DEPOSITION OF METALS. Recognition. By its penetrating smell; further, by a strip of paper moistened with sugar of lead solution becoming black when brought into a solution or an atmosphere containing sul- phuretted hydrogen. 15. Potassium sulphide (liver of sulphur}. It forms a hard 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 sul- phuretted hydrogen is evolved with effervescence, sulphur be- ing at the same time separated. 1 6. Ammonium sulphide (sulp hydrate or hydrosulphate of ammonia). When freshly prepared it forms a clear and color- less 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 charac- teristic and most disgusting, and may be compared to that of rotten turnips. It burns with a blue flame of sulphurous acid, carbonic acid being at the same time produced. It is used as a solvent for phosphorus and caoutchouc in metallizing moulds according to Parkes's method. This solution should be very carefully handled. 1 8. Antimony sulphide. a. Black sulphide of antimony (stibium sulfuratum nigrum} is found in commerce in heavy, gray, and lustreless pieces or as a fine black-gray powder, with slight lustre. It serves for the preparation of antimony baths, and for coloring copper alloys black. b. Red sulphide of antimony (stibium sulfuratum auran- tiacum) forms a delicate orange-red powder without taste or odor; it is insoluble in water, but soluble in ammonium sul- phide, spirits of hartshorn, and alkaline lyes. In connection with ammonium sulphide or ammonia it serves for coloring brass brown. CHEMICAL PRODUCTS. 431 19. Arsenic trisulphide or arsenious sulphide (orpimenf). It is found in commerce in the natural as well as artificial state, the former occurring mostly in kidney-shaped masses of a lemon color, and the latter in more orange-red masses, or as a dull yellow powder. Specific gravity 3.46. It is soluble in the alkalies and spirits of sal ammoniac. 20. Ferric sttlphide. Hard black masses generally in flat plates, which are only used for the evolution of sulphuretted hydrogen. IV. Chlorine Combinations. 21. Sodium chloride {common salt, rock salt). The pure salt should form white cubical crystals, of which 100 parts of cold water dissolve 36, hot water dissolving slightly more. The specific gravity of sodium chloride is 2.2. In electroplating sodium chloride is employed as a conducting salt for some gold baths, as a constituent of argentiferous pastes, and for precipi- tating the silver as chloride from argentiferous solutions. Recognition. An aqueous solution of sodium chloride on being mixed with a few drops of lunar caustic solution yields a white caseous precipitate, which becomes black by exposure to light and does not dissapear by the addition of nitric acid, but is dissolved by ammonia in excess. 22. Ammonium chloride (sal ammoniac) . A white substance found in commerce in the shape of tough fibrous crystals. It has a sharp saline taste, and is soluble in 2 ^ parts of cold, and in a much smaller quantity of hot water. By heat it is sub- limed without decomposition. It serves for soldering and tin- ning, and as a conducting salt for many baths. Recognition. By the sublimation on heating. By adding to a saturated solution of the salt a few drops of solution of plati- num chloride, a yellow precipitate of platoso-ammonium chloride is formed. 23. Antimony trichloride (butter of antimony}. A crystalline mass which readily deliquesces in the air. Its solution in hydro- chloric acid yields the liquor stibii chlorati, also called liquid 432 ELECTRO-DEPOSITION OF METALS. 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. 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 solu- tion blue. On evaporating to dryness, brown-yellow copper chloride is formed. It is employed in copper and brass baths as well as for patinizing. 26. Tin chloride. a. Stannous chloride or tin salt. A white crystalline salt readily soluble in water, but its solution on ex- posure to the air becomes turbid ; by adding, however, hydro- chloric acid, it again becomes clear. On fusing the crystallized salt it loses its water of crystallization, and forms a solid non- transparent mass of a pale-yellow color the fused tin salt. The crystallized, as well as the fused, salt serves for the prepa- ration of brass, bronze, and tin baths. Recognition. By pouring hydrochloric acid over a small quantity of tin salt and adding potassium chromate solution, the solution acquires a green color. By mixing dilute tin salt solution with some chlorine water and adding a few drops of gold chloride solution, purple of Cassius is precipitated ; very dilute solutions acquire a purple color. b. Stannic chloride occurs in commerce in colorless crystals, and in the anhydrous state forms a yellowish, strongly fuming caustic liquid known as the " fuming liquor of Libadius." 27. Zinc chloride (hydrochlorate or muriate of zinc; butter of zinc}. A white crystalline or fused mass which is very soluble and deliquescent. The salt prepared by evaporation generally contains some zinc oxychloride, and hence does not yield an entirely clear solution. It serves for preparing brass and zinc baths, and its solution for nickeling by immersion, solder- ing, etc. Recognition. Solution of caustic potash separates a volum- CHEMICAL PRODUCTS. 433 inous precipitate of zinc oxyhydrate, which redissolves in an excess of the caustic potash solution. By conducting sul- phuretted hydrogen into a solution of a zinc salt acidulated with acetic acid, a precipitate of white zinc sulphide is formed. 28. Zinc chloride and ammonium chloride. This salt is a combination of zinc chloride with sal ammoniac, and forms a white very deliquescent powder. Its solution serves for solder- ing and for 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. Cobalt 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 (horn silver). A heavy white powder gradually passing, by exposure to white light, through a 28 434 ELECTRO-DEPOSITION OF METALS. gradation of shades from violet to black. By precipitation from silver solutions it separates as a caseous precipitate (p. 285). At 500 F. it melts, without decomposing, to a yellow- ish fluid, which, on cooling, congeals to a transparent, tena- cious, horn-like mass. Chloride of silver is practically insoluble in water, but dissolves readily in spirits of sal ammoniac and in potassium cyanide solution. It is employed in the prepara- tion of baths for electro-silvering, for the whitening baths, and for the pastes for silvering by friction. Recognition. By its solubility in ammonia, pulverulent me- tallic silver being separated from the solution by dipping in it bright ribands of copper. 32. Gold chloride (terchloride of gold, muriate of gold, auric chloride). This salt occurs in commerce as crystallized gold chloride of an orange-yellow color, and as a brown crystalline mass, which is designated as neutral gold chloride, or as gold chloride free from acid, while the crystallized article always con- tains acid, and, hence, should not be used for gold baths. Gold chloride absorbs atmospheric moisture and becomes resolved into a liquid of a fine gold color. On being moderately heated yellowish-white aurous chloride is formed, and on being sub- jected to stronger heat it is decomposed to metallic gold and chlorine gas. By mixing its aqueous solution with ammonia, a yellow-brown powder consisting of fulminating gold is formed. In a dry state this powder is highly explosive, and, hence, when precipitating it from gold chloride solution for the preparation of gold baths, it must be used while still moist. Recognition. By the formation of the precipitate of fulmi- nating gold on mixing the gold chloride solution with ammonia. 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 sol- uble and in fact deliquescent crystals. With ammonium chloride it forms platoso-ammonium chloride (see p. 319). Both combinations are used in the preparation of platinum CHEMICAL PRODUCTS. 435 baths. The solution of platinic chloride also serves for color- ing silver, tin, brass, and other metals. Recognition. By the formation of a precipitate of yellow platoso-ammonium chloride by mixing concentrated platinic 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, pro- duct is generally employed. However, for preparing gold baths the 60 per cent, article is mostly preferred, because the potash present in all potassium cyanide varieties with a lower content renders fresh baths more conductive. However, gold baths may also be prepared with 98 per cent, potassium cyanide without fear of injury to the efficiency of the baths, while, under ordinary circumstances, a preparation with less than 98 per cent may safely be used for the rest of the baths. However, when potassium cyanide has to be added to the baths, as is from time to time necessary, only the pure preparation free from potash should be used, because the potash contained in the inferior qualities gradually thickens the bath too much. No product is more important to the electro-plater than potassium cyanide. The pure 98 to 99 per cent, product is a white transparent crystalline mass, the crystalline structure be- ing 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 tfme 436 ELECTRO-DEPOSITION OF METALS. without suffering essential decomposition. Potassium cyanide must be kept in well-closed vessels, being when exposed to the air deliquescent, and it is decomposed by the carbonic acid of the air, whereby potassium carbonate is formed while prussic acid escapes. It is a deadly poison and must be used with the utmost caution. 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, it 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 be- havior towards the air and ' in dissolving is the same as that of the pure product. Recognition. By the bitter almond smell of the solution. By mixing potassium cyanide solution with ferric chloride and then with hydrochloric acid until the latter strongly predominates, a precipitate of Berlin blue is formed. The pure salt free from potash does not effervesce on adding 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. i part = 0.820 " = 0.714 = 0.615 " = 0.460 " = By weight. = 1.230 paits = = i " = 0-875 P art = = 0.750 = 0.562 " By weight. = 1.400 parts = = I-I43 " = I. part = = 0.857 " = 0.643 " By weight. = i. 660 parts = = 1-333 " = = 1.170 " = = I. part = = 0.750 " = By weight. = 2.180 parts. = 1.780 " = i-S^o " = i-45 " = i part. 35. Copper cyanides. There is a cuprous and a cupric cya- nide ; that used for electro-plating purposes being a mixture of both. It is a green-brown powder, which should not be dried, CHEMICAL PRODUCTS. 437 since in the moist state it dissolves more readily in potassium cyanide. It is only used as a double salt, i. e. y in combination with potassium cyanide in the preparation of copper, brass, tombac, and red gold baths. Recognition. By evaporating a piece of copper cyanide the size of a pea, or its solution in hydrochloric acid to dryness in a water bath, wherein care must be taken not to inhale the vapors, and dissolving the residue in water, a green-blue solu- tion is obtained which acquires a deep blue color by the addi- tion of ammonia in excess. 36. Zinc cyanide (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 is used for brass baths. Recognition. By evaporating zinc cyanide or its solution in an excess of hydrochloric acid, zinc chloride remains behind, which is recognized by the reaction 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, however, will dissolve it with the aid of heat. At 750 F. it melts to a dark red fluid, which, on cooling, forms a yellow mass with a granular structure. It is readily dissolved by potassium cyanide, but is only slightly soluble in ammonia, differing in this respect from silver chloride. It forms a double salt with potassium 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 lustre, which break gradually and without noise. For the solution of I part of it, 4 of water are required, the solution exhibiting a pale yellow color. It precipitates nearly all the metallic salts from their solutions, some of the precipitates being soluble in an excess of the precipitating 43 8 ELECTRO-DEPOSITION OF METALS. agent. This salt is not poisonous. It serves for the prepara- tion of silver and gold baths ; its employment, however, offering no advantages over potassium cyanide except its non-poisonous properties be considered as such. Recognition. When the yellow solution is mixed with ferric chloride a precipitate of Berlin blue is formed. 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, and pure 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 must be clear. It serves as an ad- dition to some baths, and in an impure state for freeing objects from grease. Recognition. The solution effervesces on the addition of hydrochloric acid. The solution neutralized with hydrochloric acid gives with platinum chloride a heavy yellow precipitate, provided the solution be not too dilute. 40. Acid potassium carbonate or monopotassic carbonate, com- monly called bicarbonate of potash. Coloiless transparent crys- tals, which at a medium temperature dissolve to a clear solution in 4 parts of water. It is not deliquescent ; however, on boil- ing its solution it loses carbonic acid, and contains then only potassium carbonate. It is employed for the preparation of certain baths for gilding by simple immersion. 41. Sodium carbonate (washing soda). It occurs in com- merce as crystallized or calcined soda of various degrees of purity. The crystallized product forms colorless crystals or masses of crystals, which, on exposure to air, rapidly effloresce and crumble to a white powder. By heating, the crystals also lose their water, a white powder, the so-called calcined soda, remaining behind. Soda dissolves readily in water, and serves as an addition to copper and brass baths, for the preparation CHEMICAL PRODUCTS. 439 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 I part of the crystallized product. 42. Sodium bicarbonate (baking powder). A dull white powder soluble in 10 parts of water of 68 F. On boiling, the solution loses one-half of its carbonic acid, and then contains sodium carbonate only. 43. Calcium carbonate (marble, chalk}. When pure it forms a snow-white crystalline powder, a yellowish color indicating a content of iron. It is insoluble in water, but soluble, with effer- vescence, in hydrochloric, nitric, and acetic acids. In nature, calcium carbonate occurs as marble, limestone, chalk. In the form of whiting (ground chalk carefully freed from all stony matter) it is used for the removal of an excess of acid in acid copper baths, and mixed with burnt lime as an agent for freeing objects from grease. 44. Copper carbonate. Occurs in nature as malachite and allied minerals. The artificial carbonate is an azure-blue sub- stance, insoluble in water, but soluble, with effervescence, in acids. Copper carbonate precipitated from copper solution by alkaline carbonates has a greenish color. Copper carbon- ate is employed for copper and brass baths, and for the re- moval of an excess of acid in acid copper baths. Recognition. Dissolves in acids with effervescence; on dip- ping a riband of bright sheet-iron in the solution, copper 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 alkaline carbonates is a combination of zinc carbonate with zinc oxy- hydrate. It serves for brass baths in connection with potassium cyanide. Recognition. In a solution in hydrochloric acid, which is 44 ELECTRO-DEPOSITION OF METALS. formed with effervescence, according to the reactions given under zinc chloride (27). 46. Nickel carbonate. A pale apple-green powder, insoluble in water, but soluble, with effervescence, in acids. It is em- ployed for neutralizing nickel baths which have become acid. Recognition. In hydrochloric acid, it dissolves, with effer- vescence, to a green fluid ; by the addition of a small quantity of ammonia, nickel oxyhydrate is precipitated, which, by add- ing ammonia in excess, is redissolved, the solution showing a blue color. 47. Cobalt carbonate. A reddish powder, insoluble in water, but soluble in acids, the solution forming a red fluid. VII. Sulphates and Sulphites. 48. Sodium sulphate (Glaubers 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 on glowing, 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 concentrated solution compounded with platinic chloride gives a yellow pre- cipitate of platoso-ammonium chloride, while a solution mixed with a few drops of hydrochloric acid gives with barium chlo- ride a precipitate of barium sulphate. 50. Aluminium-potassium sulphate (potash-alum). Color- less 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. CHEMICAL PRODUCTS. 441 Recognition. On adding sodium phosphate to the solution a jelly-like precipitate of aluminium phosphate is formed, which is soluble in caustic potash, but insoluble in acetic acid. 51. Ammonium- alum is exactly analogous to the above, the potassium sulphate being simply replaced by ammonium sul- phate. It is for most purposes interchangeable with potash- alum. On glowing ammonium-alum the ammonium sulphate is lost, pure alumina remaining behind. Ammonium-alum is used for preparing a bath for zincking iron and steel by im- mersion. Recognition. The same as potash-alum. On heating the comminuted ammonium-alum with potash lye an odor of am- monia becomes perceptible. 52. Iron sulphate (iron protosulphate, ferrous sulphate or green vitriol). Pure green vitriol forms bluish- green transparent crystals of a sweetish astringent taste, which readily dissolve in water. Crude green vitriol is a green crystalline substance, often yellowish on the exterior owing to the formation of ferric compounds with the aid of atmospheric oxygen. It generally contains, besides ferrous sulphate, the sulphates of copper and zinc as well as ferric sulphate. On account of the tendency to peroxidation, green vitriol and other ferrous compounds should not be exposed to the air any more than is necessary. Green vitriol is employed for the preparation of iron baths, and for the reduction of gold from its solutions. Recognition, By compounding the green solution with a few drops of concentrated nitric acid, a black-blue ring is formed on the point of contact. On mixing the lukewarm solution with gold chloride, gold is separated as a brown powder, which by rubbing acquires the lustre of gold. 53. Iron- ammonium sulphate. Green crystals which are con- stant in the air and do not oxidize as readily as green vitriol. 100 parts of water dissolve 16 parts of this salt. It is used for the same purposes as green vitriol. 54. Copper sulphate (cupric sulphate or blue vitriol}. It forms blue crystals, of which 100 parts of cold water dissolve 44 2 ELECTRO- DEPOSITION OF METALS. about 40, and the same volume of hot water about 200 parts. Blue vitriol which does not possess a pure blue color, but shows a greenish lustre, is contaminated with green vitriol, and should not be used for electro-plating purposes. Blue vitriol serves for the preparation of alkaline copper and brass baths, acid copper baths, etc. Recognition. By its appearance, as it can scarcely be mis- taken for anything else. A content of iron is recognized by boiling blue vitriol solution with a small quantity of nitric acid, and adding spirits of sal ammoniac in excess ; brown flakes in- dicate iron. 55. 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 acetate of copper (verdigris), copper vitriol, or cuprous oxide. 56. 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 glow- ing 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 at the boiling-point. Zinc sulphate is employed for the preparation of brass and zinc baths. Recognition. By mixing zinc sulphate solution with acetic acid and conducting sulphuretted hydrogen into the mixture, a white precipitate of zinc sulphide is formed. A slight content of iron is recognized by the zinc sulphate solution, made alka- line by ammonia, giving with ammonium sulphide a somewhat colored precipitate instead of a pure white one. However, a slight content of iron does no harm. 57. 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- CHEMICAL PRODUCTS. 443 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 the heated solution previously strongly acidulated with hydrochloric acid. 58. Nickel- ammonium sulphate. It forms green crystals of a somewhat paler color than nickel sulphate. This salt dissolves with more difficulty than the preceding, 100 parts of water dis- solving only 5.5 parts of it. It is used for the same purposes as the nickel sulphate, and is also recognized in the same manner. 59. Cobalt sulphate. Crimson crystals of a sharp metallic taste, which 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 be- come thereby transparent and rose-colored. The salt is used for cobalt baths for electro-cobalting and 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 solu- tion of the salt strongly acidulated with hydrochloric acid with solution of potassium nitrate, a reddish-yellow precipitate is formed. 60. Cob alt- ammonium sulphate. This salt forms crystals of the same color as cobalt sulphate, which, however, dissolve more readily in water. 61. Sodium sulphite and bisulphite. a. Sodium sulphite. Clear, colorless, and odorless crystals, which are rapidly trans- formed into an amorphous powder by efflorescence. The salt readily dissolves in water, the solution showing a slight alkaline 444 ELECTRO-DEPOSITION OF METALS. reaction due to a small content of sodium carbonate. It is em- ployed in the preparation of gold, brass, and copper baths, for silvering by immersion, etc. Recognition. The solution when mixed with dilute sulphuric acid has an odor of burning sulphur. b. Sodium bisulphite. Small crystals, or more frequently in the shape of a pale yellow powder with a strong odor of sul- phurous acid and readily soluble in water. The solution shows a strong acid reaction and loses sulphurous acid in the air. It is employed in the preparation of alkaline copper and brass baths. Both the sulphite and bisulphite must be kept in well-closed receptacles, as by the absorption of atmospheric oxygen they are converted to sulphate. 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 glowing heat, and on cooling congeals to an opaque, crystalline mass. It is employed in the preparation of desilvering baths and for producing a dead lustre upon gold and gilding. For these purposes it may, however, be replaced by the cheaper sodium nitrate, sometimes called cubic nitre or Chile saltpetre. Recognition. A small piece of coal when thrown upon melt- ing saltpetre burns fiercely. When a not too dilute solution of saltpetre is compounded with solution of potassium bitartrate saturated at the ordinary temperature, a crystalline precipitate of tartar is formed. 63. Sodium nitrate (cubic nitre or Chile saltpetre). Color- less crystals, deliquescent and very soluble in water ; the solu- tion shows a neutral reaction. It is used for the same purposes as potassium nitrate. 64. Mercurous nitrate. It forms small, colorless crystals, CHEMICAL PRODUCTS. 445 which are quite transparent and slightly effloresce in the air. On heating they melt and are transformed, with the evolution of yellow-red vapors, into yellow-red mercuric oxide, which, on further heating, entirely evaporates. With a small quantity of water, mercurous nitrate yields a clear solution ; by the further addition of water it shows a milky turbidity, which, however, disappears on adding nitric acid. It -is employed for quicking the zincs of the elements and the objects previous to silvering, and for brightening gilding. For the same purpose is also used : 65. Mercuric nitrate. It is difficult to obtain this salt in a crystallized form. It is generally sold in the form of an oily, colorless liquid, which, in contact with water, separates a basic salt. This precipitate disappears upon the addition of a few drops of nitric acid, and the liquid becomes clear. Recognition. A bright riband of copper dipped in solution of mercurous or mercuric nitrate becomes coated with a white amalgam, which dissapears upon heating. 66. Silver nitrate (lunar catistic}. This salt is found in commerce 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 white, or gray, or black color, according to the nature of the mould employed, in which form it constitutes the lunar caustic for surgical uses. For our purposes only the pure, crystallized product, free from acid, should be employed. The crystals dissolve readily in water. In making solutions of this and other silver salts, only distilled water should be used ; all other waters, owing to the presence of chlorine, produce a cloudiness or even a distinct precipitate of silver chloride. In the heat the crystals melt to a colorless, oily fluid, which, on cooling, con- geals 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 moulds. 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 ammonia. IX. Phosphates and Pyrophosphates. 67. Sodium phosphate. Large, clear crystals, which readily effloresce, and whose solution in water shows an alkaline reac- tion. It is employed in the preparation of gold baths and for the production of metallic phosphates for soldering. Recognition. The dilute solution compounded with silver nitrate yields a yellow precipitate of silver phosphate. 68. Sodium pyrophosphate. It forms white crystals, which are not subject to efflorescence, and are soluble in 6 parts of water at a medium temperature ; the solution shows an alka- line reaction. Sodium pyrophosphate also occurs in commerce in the form of an anhydrous white powder, though it may here be said that the directions for preparing baths refer to the 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 show- ing an acid reaction, should be rejected. It is employed in the preparation of platinum baths. X. Salts of the Organic Acids. 70. Potassium bitartrate {cream of tartar}. The pure salt forms small transparent crystals of an acid taste, and 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 finely powdered state, purified tartar is called cream of tartar. It is employed for the preparation of the whitening silver baths, for those of tin, and for the silvering paste by friction. CHEMICAL PRODUCTS. 447 71. Potassium sodium tartrate (Rochelle or Seignette salt). Clear colorless crystals, constant in the air, of a cooling bitter saline taste, and soluble in 2.5 parts of water of a medium tem- perature. The solution shows a neutral reaction. This salt is employed in the preparation of copper baths free from cyanide, as well as of nickel and cobalt baths, which are to be decom- posed in the single cell apparatus. 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 TOO parts of cold water dissolve 5 parts, while a like volume of hot water dissolves 50 parts. The solution shows a slightly acid reaction. The only use of this salt is for the preparation of antimony baths. Recognition. The solution compounded with sulphuric, nitric, or oxalic acid yields a white precipitate, insoluble in an excess of the cold acid. Sulphuretted hydrogen imparts to the dilute solution a red color. Hydrochloric acid effects a pre- cipitate, 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 of 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, as well as 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. 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 44-8 ELECTRO-DEPOSITION OF METALS. 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 formula. B. VARIOUS APPARATUS AND INSTRUMENTS. Glass balloons and flasks. These are spheres of thin blown glass, Fig. 138, with necks of various dimensions in length and diameter. They are employed for heating acids, FIG. 138. dissolving metals, and a great many other uses. They should be placed upon triangular supports of iron and at a certain distance from the fire, from the direct action of which they are to be protected by the intervention of a piece of wire gauze or its equivalent. The thinner they are the more easily they bear sudden changes of temperature. They are preferable to porcelain evaporating dishes for dissolving gold, because there is much less danger of losing a part of the product by spurting. Evaporating dishes or capsules. These are usually vessels of porcelain, and are intended to bear a high temperature. The best are thin and uniformly so. Like glass flasks, they should be supported above the fire upon an iron stand and wire gauze. As far as practicable they should be gradually heated and cooled. When taken from the fire they should be placed upon rings made of plaited straw. They are made with or without lips, and some have a socket for a wooden handle. Glass evaporating dishes are not durable. Glass jars. These are glass vessels, generally cylindrical, closed at one end, and of different capacities. They are employed for small gilding, silvering, and electro- VARIOUS APPARATUS AND INSTRUMENTS. 449 plating baths in the cold. They are handy and serviceable for amateurs, because their transparency permits the progress of the operation to be observed at all times. Crucibles. These are vessels, the shape of which is gen- erally an inverted truncated cone, Fig. 139, the smaller end being closed, and the larger open. Sometimes the opening is triangular. FlG - I 39- Crucibles are made of many kinds of materials : metals, refractory clay, stoneware, porcelain, plum- bago or graphite, etc. They are generally provided with a cover of the same material, and are raised above the grate bars of the furnace by means of bricks or cylinders of clay. Metallic crucibles may be heated rapidly, but the others require to have their temper- ature raised gradually and carefully. They are employed for the preparation of many salts, for the fusion of metals, etc. Non-metallic crucibles are rarely used for more than one operation. Hydrometers. These are glass instruments resembling ther- mometers in outward appearance, but having a large bulb near the bottom. They are used for testing the specific gravity of liquids, or, in other words, to test their density as compared with that of pure water. The liquid to be tested may be placed in a narrow glass jar together with the hydrometer, or'may be contained in any other vessel. The instrument floats in the liquid to be tested, with its bulb below the surface and its stem standing above the surface. This stem is graded into degrees similar to that of a thermometer, and shows the depth of the bulb beneath the surface. In pure water the bulb sinks down to the o mark, or to i.ooo as marked on some scales, i.ooo being taken to represent the density of water at a temperature of 60 F. As the density of water increases by the addition of salts or of liquids having a greater density than water, the bulb is forced upwards, and the scale then registers so many degrees greater density than water. Three differently graduated hydrometers are in use, viz., 29 450 ELECTRO- DEPOSITION OF METALS. hydrometers graded to read direct the specific gravity of liquids in comparison with that of water, taking this as represented by i.ooo; hydrometers graded by a scale adopted by Mr. W. Twaddell, and known as Twaddell's hydrometers ; and hydrom- eters graded by a scale adopted by M. Baume, and named Baume's hydrometers. The difference between the three grad- ings is shown in the following table: Table showing readings of different hydrometers. Specific gravity. Baume. Twaddell. Specific gravity. Baume. Twaddell. .817 40 _ 1.250 _ 500 .827 38 1.263 30 837 36 1.300 60 .847 34 1.321 35 .856 3 2 1-350 7 .871 .880 30 28 z 1.385 1.400 40 80 .892 26 1.450 90 .903 24 1.454 45 .915 22 1.500 100 .928 20 1.532 50 .942 18 l -SS no 955 16 1. 600 120 .970 H 1.618 55 .985 12 1.650 I 3 I.OOO o or 10 1.700 I 4 1.036 5 1.714 60 1.050 10 1.750 I|0 J -75 10 i. 800 160 .100 20 1.823 65 .116 15 1.850 170 .150 3 1.900 1 80 .161 20 1.946 70 .200 . 40 1.95 190 .210 25 It will be seen that every degree Twaddell represents 0.005 in the specific gravity hydrometer, and every 10 represents 0.050. To convert degrees Baume into readings showing direct specific gravity, subtract the readings on Baume's scale from the number 144, and divide this by the difference. For example, 144 66 = 1^4 = 1.846, the specific gravity of a 7 8 liquid registering 66 on a Baume hydrometer. Baume has VARIOUS APPARATUS AND INSTRUMENTS. 451 FIG. 140. one hydrometer for liquids lighter than water (the readings of which are given in the first 16 sets of figures in the foregoing table), and one for liquids heavier than water. Filters. Filtering a solution, a bath, or any other liquor, consists in causing it to pass through a permeable substance, the pores or meshes of which are sufficiently closed to retain all the undissolved substances, which are thus separated from the liquid part. Filters are of very different materials and shapes. Cloth, muslin, etc., are coarse filters or strainers, made in the form of pockets. Their filtering power is considerably improved by covering them with a layer of sand, wool, boneblack, etc. These latter substances them- selves, properly supported, will act as filters. Felted wool (generally rabbit's hair) is made in the shape of a conical pocket (Fig. 140), but is suited only for neutral sub- stances. Alkalies destroy it rapidly. Concentrated acids are filtered through amianthus, or asbestos, compressed in the neck of a glass funnel upon broken fragments of glass. The most useful filtering material, however, is unsized paper. This filter (Fig. 141) is prepared by folding diagonally a square piece of porous paper, which thus prepared forms a triangle. This is again folded in half. Then, beginning at one edge, smaller folds are made alternately to the right and to the left, but all converging towards the point, like a fan. The filter is now partially opened, trimmed on top, and intro- duced into the funnel, care being had that all the projecting edges rest against it. If it be feared that the filter will not resist the weight of the liquid, the point is twisted to the left or to the right, and while it is still held be- tween two fingers of the left hand, the whole filter is inverted, so that the inward folds become the outward 141. Fir,. 142. 452 ELECTRO-DEPOSITION OF METALS. ones. A filter with such a rounded point is better supported in the funnel, and filters more rapidly. This method is preferable for rapid filtration ; but if it is de- sired to recover precipitates, the filter represented by Fig. 142 is more suitable. A circular sheet of paper is twice doubled up, and by carefully opening it three thicknesses of paper are laid on one side, leaving one single thickness on the other side. Siphons. The most simple and handy siphon, in many cases, is a piece of lead pipe bent so as to have two unequal branches, the smaller of which plunges into the liquid to be drawn oft". A section of India-rubber tube may be employed for similar purposes. But as these materials may be chemically acted upon by various solutions, glass siphons are used, with or without a suction tube (Figs. 143 and 144). FIG. 143. FIG. 144. For siphoning corrosive solutions which cannot be touched with the fingers, a siphon with a suction tube is used (Fig. 143). The shorter leg is plunged into the liquid and the longer one closed with the finger or an India-rubber pad pressed against it; then, with the mouth, suction should be VARIOUS APPARATUS AND INSTRUMENTS. 453 carefully applied at the lateral suction tube until the liquid fills the longer leg. If there be any danger of inhaling a poisonous vapor, the action of the mouth may be replaced by an India-rubber ball fastened to the suction tube. The longer branch of the siphon is closed as before, and the ball compressed in order to remove the air. By its elasticity the ball resumes its former volume, thus producing a suction which starts the siphon in action. Stirring rods. These are rods made of various materials, and are employed for mixing together liquids or pastes, or liquids and pastes, or solids with liquids, or various solids in the dry state. Their length and thickness should be suited to the volumes to be mixed. Suitable stirring rods are those which have no chemical action upon the substances with which they are brought in contact; neither should they become impregnated with them. Rods of glass, stoneware, or porcelain are decidedly the best. Wood and most metals should be avoided, because the former is absorbent and the latter are corroded and easily oxidized. The operator should always have near at hand a complete assortment of glass stirrers of various sizes, and with fused or rounded ends, in order not to scratch the vessels in which he operates. APPENDIX. FIG. 145. CHECK VOLTMETER. UNDER " Electro-Plating Arrangements in Particular," p. 89, et seq., reference has been made to various styles of voltmeters. In addition attention may be called here to the check volt- meter, Fig. 145, manufactured by the Hanson & Van Winkle Co., of Newark, N. J., and de- signed for small plants or for connection with every tank in larger establishments. The cost of the large volt- meters is an obstacle to their general use, except in the main circuit, where they are usually placed at a distance from the tanks, and do not show the variation in voltage between the dynamo and tanks caused by resistance of the conductors. The check voltmeter can be connected with each tank, and is of great advantage to the plater who is operating baths requiring different voltages, for by touching the 'button of the switch the tension of current at each tank can be instantly de- termined. The instrument is calibrated from a standard volt- meter and is reliable. It cannot be left in circuit, and for this (454) UNIVERSITY APPENDIX. 455 reason a switch is provided. The price of the instrument is $2.50. The Bossard Mechano- Electroplating Tanks. These tanks are patented devices in which the work to be plated is automatically drawn through the bath at a controllable rate of speed. There are two styles of these devices, namely, the " long tank" and the " circular tank" FIG. 146. The long tank, Figs. 146 and 147, is made of wood or plate steel. Two rigid bridges span the tank longitudinally, their top faces being mounted their entire length by a metal strip, which can be directly connected to the cathode rheophore of dynamo. Preferably the cathode element is brought into the apparatus by a connection to the copper strips, which are found extend- ing on each side at bottom of bridge. Upon each of the bridges is traveling an endless chain encircling the tank longi- tudinally. Sprocket wheels upon a shaft at one end of tank, which are driven by a simple and effective mechanical move- ment consisting of a ratchet wheel, pallet upon rocker arm, pitman and slide crank, give motion to the chains. An adjust- able wrist-pin on slide-crank, holding one end of pitman, is the means whereby the shortening and lengthening of stroke of the latter, and with it the path of pallet on ratchet-wheel, and con- 456 APPENDIX. sequently the speed of sprocket-wheel shaft, is fixed. The speed of the chain is determined by the time it is desired to give the work to be plated in the bath. The work is hung into the bath on hooks or frames at one end of tank, suspended from each side of bridge. Engaging in the chain it moves with the latter, and when it has reached the other end in its travel through the bath, is removed as sufficiently plated. Electric contact is made, either at juncture of hook with metal strip on top face of bridge, or hook and copper strip on side of bridge, or at both points. Along the sides and through the middle of the bath are three rows of anodes. For the purpose of controlling the anode surface in the bath, the anodes are suspended in small numbers, from short sections of rod, which are individ- ually and movably connected by switch to the feed-rods FIG. 147. charged with the anode element of dynamo. This arrangement enables the operator to use such amount of anode surface in the bath as will insure good work. In the manipulation of this tank it is the operator's task to fix the time the work is to take in its travel through the bath, adjust the speed of chain accordingly, regulate at the switch- board the electric current going into the bath, pass the work through lye and cleansing dips, suspend it in the bath, the hooks holding same to engage in the moving chain. The work requires no care while going through the bath. Arriv- APPENDIX. 457 ing at the other end it is taken out by a workman, whose further duty it is to pass the work through hot water and dry it off in the usual manner. The long tank is highly spoken of by manufacturers of hard- ware for the deposition of copper, brass and bronze on steel goods and gray-iron castings, among its users being The Yale and Towne Manufacturing Co., Stamford, Conn., The Russell and Erwin Manufacturing Co., New Britain, Conn., and The Stanley Works, New Britain, Conn. The circular tank, Figs. 148 to 150, consists chiefly of a FIG. 148. large wooden tub in which a circular carrier is caused to re- volve upon a horizontal plane. Fig. 148 shows an exterior view of the tank, Fig. 149 a plan of the tank and carrier, and Fig. 150 section and partly front elevation of the tank, carrier and machinery. A peculiarity of the wooden tub is its open central space which gives it the quality of a circular trough. In the construction of the tank the size and shape of the work to be plated determine the dimensions of this trough. The 458 APPENDIX. quantity of work decides the general dimensions of the tank and of the open central space. The carrier is constructed to hold two rows of work of con- siderable lineal capacity and to move above bath and tank. It is mounted upon a perpendicular shaft, and this by means of a worm gear at lower end and properly supported within the open central space is revolved, and its speed adjusted by a FIG. 149. mechanical contrivance similar to the one applied for the same purpose to the long tank. In this device the general principle is recognized which underlies the long tank, but somewhat different results attend its operation, attributable to its shape. The arrangement for controlling the anode surface in the bath is the same, the deri- vation of the frictional electric contact between work and cathode bar is similar; but on account of its circular shape APPENDIX. 459 and movement the work, suspended from the carrier as it passes through the bath in its circular course, returns to its original starting point when completing its revolution. This enables the operator to occupy one position, in which he con- tinuously supplies the bath with work and withdraws the same as it returns to him plated. The walking forward and back in FIG. 150. SECTION AND PARTLY FRONT ELEVATION OF CIRCULAR TANK, CARRIER AND MACHINERY. the course of attention the old-style tanks require, is thereby entirely saved, and a great point of economy gained. The cleansing tanks, hot and cold water, pickles and dips are placed near the operator's position at the circular tank, which at once simplifies and brings closer together the general operations of the plating room, saves floor space, and adds to the facilities of keeping the room clean and dry. It times the operation of UNIVERSITY APPENDIX . plating in the bath automatically and insures uniformity of product. The advantages claimed by the inventor from the shape and general construction of these devices are as follows : 1. The work to be plated, as it is drawn through the bath, continuously stirs the latter, thereby keeping it in active chemical condition. The hydrogen bubbles formed' on the work are constantly dislodged, the result being a rapid, smooth, and homogeneous deposit. 2. The frictional contact derived from the bearing of the hooks carrying the work into the bath against the cathode bar, insures a keen, never fading, electric action to enter the bath. The contact points are always clean and sure. 3. The movement through the bath passes the work in con- stantly changing positions before the anodes while undergoing the process of deposition. 4. To increase the movement of the work and vary the nature of the motion during its travel through the bath, small deflecting devices are introduced at desired distances along and upon the cathode bars, and for special work, revolving hooks have been used to great advantage. 5. The proximity of the work to the anode in the plating bath is well known to cause conditions favorable or unfavorable to the formation of a good deposit. Experiments have plainly shown and the daily application of these devices proves that the distance between the work and the anode can be considerably reduced and the intensity of the current increased without danger of burning the work when the latter is gently moved. By reducing distance between anode and cathode, the resist- ance upon the dynamo is accordingly diminished, and this con- dition is very desirable in nickel and other solutions which are of a neutral and non-conducting nature. In may finally be observed that while in the electro-deposi- tion of metals the moving of the work in the bath is not new, and its effects are well known and appreciated, the manner in which the movement is produced in these devices and the idea APPENDIX. 461 of having the work enter the bath, pass through the same, and approach a desired point for removal at an adjustable rate of speed, are both new and novel, and the results, as a conse- quence to construction and conditions thereby created in the bath, can be readily understood. The Bossard Mechano-Electroplating Tanks are manufac- tured tiy the Schreiber & Conchar Manufacturing Co., of Dubuque, Iowa. USEFUL TABLES. Table of elements with their symbols, atomic weights, and specific gravities. Name. Sym- bol. Atomic weight. Specific gravity. N -<- :tT Atomic weight. Specific- gravity. Al Sb As Ba Be Bi B Br Cd Cs Ca C Ce Cl Cr Co Cu D E F Au H In I Ir Fe La Pb Li Mg Mn Hg 27.4 122 75 137 9-3 208 ii 80 I 12 133 40 12 92 35-5 58.8 634 95 112.6 19 197 75.6 127 197.4 56 92 207 7 24 55 200 2.67 6.72 5-63 4.00 2.IO 9-799 2.68 2.97 8.67 3.10 3-50 245 6.81 8.50 8.88 J 9-5 0.069 4.98 21.15 7.70 11.38 0.59 1.74 8.co '3-59 Molybdenum . . . Nickel Mo Ni Nb N Os O Pd P Pt K Rh Rb Ru Se Si Ag Na Sr S Ta Te Tl Th Sn li W U V Y Zn Zr 96 58 94 14 199-4 16 106.6 3 1 197.4 39-1 104.4 854 1044 794 28 108 2 3 87.5 32 182 128 204 231 118 120 5!-3 68 65 89.6 8.60 8.6 6.67 0.972 21.3 i. 088 1 1.8 1.84 21.15 8.865 I2.IO I. 5 1140 4.28 2.49 10.50 0.972 2-54 2.045 10.78 6.18 11.86 7.70 7.29 5-30 19.10 1840 5-50 7.2 4.20 Arsenic Oxvcren Palladium Phosphorus .... Platinum Cadmium .... Ruthenium Chlorine Chromium Cobalt Silver Didymium Strontium Gold Hydrogen Thallium Tin Lanthanum .... Lead Vanadium Yttrium Magnesium Manganese 462 APPENDIX. Table of chemical and electro- chemical equivalents. Name of substance. Sym- bol. Specific gravity. Chemical equiva- lent. Electro- chemical equi- valent. Milligrammes. Weights decomposed by i ampere in I hour. In grammes. Hydrogen H j o 01036 O O37C Aluminium Al 26 11 7 O I42CO "HJ/3 O r i -27 Sb 68 122 I 26880 ^D 1 Jl A C7CQ As 7C o 78000 4o/y 2 8l2C Cobalt Co j'/ 8 7 Jj 2Q o 30680 I IO62 Copper Cu 88 11 8 O 77C7O I IQ2 Gold Au IQ 2 08 ^ I O223O 3 6862 Fe 28 O 2Q I 2O L ea( j Pb D 117 IO7 I 07640 -7 ggl2 Nickel Ni 86 2Q C o 30680 I IO62 Pt 98 6 Arr TQ r 1 08 112 34O o- u y/.) Tin Sn 1U O 1 "? 32 7 o 34010 i 2262 Zn i'J 72 O-''/ en o 61 360 2 212*5 * j? With the assistance of this table it can be calculated how long a measured surface has to remain in the bath in order to acquire a deposit of determined weight with the most suitable current density. Suppose the time is to be determined which a square decimetre of surface has to remain in the nickel bath in order to acquire a deposit of y 1 ^ millimetre thick with a cur- rent density of 0.5 ampere. First calculate the weight of the deposit by multiplying the surface in square millimetres with the thickness and specific gravity. One square decimetre is equal to 10,000 square millimetres, which, multiplied by T ^ milli- metre, gives as a product 1000, which, multiplied by the specific gravity of nickel 8.6 gives 8600 milligrammes = 8.6 grammes. Since, for the regular deposit per square decimetre, a current density of 0.5 ampere is required, and i ampere de- posits, according to the above table, 1.1062 grammes in i hour, y 2 ampere deposits 0.5331 gramme in i hour, and, therefore, about 1 6 hours will be required for the deposition of 8.6 grammes. According to this example, the time, for instance, can also be APPENDIX. 463 calculated 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. Suppose 50 grammes of silver are to be deposited upon i dozen of spoons, and the most suitable current density is 0.2 ampere per square decimetre ; if the surface of I spoon represents i.io square decimetres, the surface of I dozen spoons of equal size is 13.2 square decimetres. Hence, they require 13.2 x 0.2 = 2.64 amperes; now, since I ampere de- posits in one hour 4.05 grammes of silver, 2.64 amperes deposit in the same time 10.7 grammes of silver, and with this current the dozen spoons must remain about 4^ hours in the bath for the deposition of 50 grammes of silver upon this surface. Table showing the value of equal current volumes as expressed in amperes per square decimetre, per square foot, and per square inch of electrode surface. Amperes per square decimetre. V) &> % 5 - 3 o,cr .J fsJ II Ifj Isj Amperes per square decimetre. l*^ <0 11 if |:-s i ^- a Amperes per square decimetre. S rt X |^ ^g II ^ = Ampees per square inch. 0.05 0.46 0.0032 0.8 743 0.0516 6.20 57-6 0.4 0.054 -5 0.0035 0.86 8 -555 6.46 60 0.4167 0.077 0.72 0.005 0.9 8.36 0.0581 7 65.0 0.4516 O.I o.93 0.0064 0-93 8.64 0.06 7-53 70 0.4861 O.I I i 0.0069 0.97 9 0.0625 7-75 72.0 -5 0.15 1.44 O.OI 9.29 0.0645 8 74-3 0.5161 0.2 1.86 0.0129 i. 08 10 00694 8.61 80 -5555 0.22 2 0.0139 1.09 10.28 0.07 9 83.6 0.5806 0-3 2.79 0.0193 1.24 11.52 0.08 9-30 86.4 | 0.6 0.31 2.88 0.02 i-39 12.96 0.09 9.69 90 0.6250 0.32 3 O.O2O8 '55 14.4 C.I 10. 92.9 0.6452 0.4 3-71 0.0258 2 1 8.6 0.1290 10.76 100 : 0.6944 0-43 4 0.0278 2.15 20 0.1389 10.85 100.8 0.7 0.46 o-5 4-32 4.64 0.03 0.0323 3 3.10 27.9 28.8 0.1935 O.2 I2.4O 13-95 115.2 129.6 0.8 0.9 0-54 5 0.0348 3-23 30 0.2083 I S-S 144.0 1 0.6 5-57 0.0387 4 37-i 0.2581 20 185.8 1.2903 0.62 5.76 0.04 4-30 40 0.2778 21.53 2CO 1.3889 0.65 6 0.0417 4.60 43-2 0-3 3 278.7 ! 1.9355 0.7 6.50 0.0452 5 46.4 0.3226 31.0 288 2 o-75 7 0.0486 5.38 50 0.3478 32.3 300 2.0833 0.77 7.20 0.05 6 55-7 0.3871 46.5 432.0 3 464 APPENDIX. By this table the current density may be expressed in amperes per square decimetre, square foot, or square inch, any of them being given. Thus a current of I ampere per square decimetre has the same electrolytic value as one of 9.29 amperes per square foot, or 0.0645 P er square inch. To find the value of intermediate numbers, not shown above, add to- gether the various numbers representing the hundreds, tens, units, and decimals of the given quantity. Thus 27.5 amperes per square decimetre (=20+7+5) are equivalent to 185.8 + 65+4.64=255.44 amperes per square foot, or 1.290340.4516+ 0.0323 = 1.7742 amperes per square inch. Table showing the specific electrical resistances* of different sul- phuric acid solutions at various temperatures (Fleeming Jen kin). Specific Temperatures (Fahrenheit). gravity of acid. 32 39.2 46.4 53.6 60.8 68 75.2 82.4 .10 37 1.17 1.04 0.92 0.84 0.79 0.74 0.71 .20 33 i. ii o.93 0.79 0.67 o-57 0.49 0.41 2 5 3 1 1.09 0.90 0.74 0.62 0.51 0-43 0.36 30 .36 i.i3 0.94 0.79 0.66 0.56 o.47 0-39 .40 .69 1.47 1.30 1.16 1.05 0.96 0.89 0.84 5 2.74 2.41 2.13 1.89 1.72 1.61 1.32 1.43 .60 4-32 4.16 3-62 3-" 2-75 2.46 2.21 2.02 .70 9.41 7.67 6.25 5-i2 4.23 3-57 3.07 2.71 Table showing the specific electrical resistances* of different copper sulphate solutions at various temperatures {Fleeming Jenkin). No. of parts of copper sulphate dissolved in 100 parts of water. Temperatures (Fahrenheit). 57.2 60.8 C 64.4 68 75.2 82.4 C 86 8 12 16 20 24 28 45-7 36.3 31.2 28.5 26.9 24.7 43-7 34-9 30.0 27-5 25.9 234 41.9 33-5 28.9 26.5 24.8 22.1 40.2 32.2 27.9 25.6 23-9 21.0 37-i 29.9 26.1 24.1 22.2 18.8 34.2 27.9 24.6 22.7 20.7 16.9 32.9 27.0 24.0 22,2 20.0 16.0 * By the term "specific resistance," in the above tables, is meant the absolute re- sistance in ohms of a column of the liquid I square centimetre in cross-section and I centimetre long; in other words, it is the resistance of a cubic centimetre of the liquid. The diminution of resistance accompanying a rise of temperature should be especially marked. APPENDIX. 465 Table of the electro-motive force of elements. Name of element. Constitution. Electro- motive force in volts. Authority. Amalgamated zinc and cop- f 0.886 Clark and Sabine Smee per in dilute sulphuric acid (1:12). Amalgamated zinc in sul- \ 0.861 (0.719 C I 008 Sprague. De la Rive. Clark and Sabine Daniell phuric acid; platinized silver, or platinum in sul- phuric acid (i : 12). 1 !- I0 7 1 0.541 [1.192 Sprague. De la Rive. Naclari. Clark and Sabine do phuric acid (1:4); cop- per in saturated solution of copper sulphate. Zinc in dilute sulphuric acid i.u/y do. do. do. f O Q?8 Sprague. De la Rive. Naclari. Clark and Sabine Leclanche (i : 12) ; copper as above. Zinc in sal ammoniac carbon 1 0.98 {I 4.81 Du Moncel. do with manganese peroxide in sal ammoniac. Zinc in solution of common 1.561 1.942 1.259 ( I AQI Sprague. De la Rive. Beetz. Marie Davy salt; carbon with manga- nese peroxide in common salt solution. i^yj 1 1.360 1 1-34 f I C24. Naclari. Du Moncel. (i : 12) ; carbon in mercu- rous sulphate. At 3^4 i 1-542 1 1.482 [1.440 Sprague. Naclari. Du Moncel. do (i : 12); platinum in fum- ing nitric acid. 1.956 f I C2A Clark and Sabine. nitric acid of 1.38 sp. gr. i i.^q. I 1-542 f I Q6A Sprague. do fuming nitric acid. I !-95 {i 888 Du Moncel. Clark and Sabine do nitric acid of 1.38 sp. gr. 1.941 1.880 f 2 O28 Beetz. Naclari. Grenet chromate of potassium. \ I-905 ( 2.120 I 82C Sprague. Naclari. mate of potassium. &o5 30 466 APPENDIX. Table showing the solubility of various substances. Substances of which I part is soluble In water In alcohol of 59 F. of 59 F. of 212 F. 6.5 4.0 0-75 5-P 0.6 0.8 i-5 7000 2.0 3-0 0.9 o-5 readily soluble 10 3-0 sparingly soluble 0.8 I.O 2.O soluble 2.8 4.0 4.0 0-3 2.0 0-3 decomposes 0.6 i-3 very soluble M 0-3 soluble very soluble 2.O very soluble readily soluble 1.2 1.4 sparingly soluble very soluble 0-3 -5 soluble 2-5 1.0 I.O very soluble I.O insoluble, soluble, soluble, insoluble, soluble, soluble, insoluble, readily soluble, soluble, insoluble, insoluble, soluble, soluble. insoluble, sparingly soluble. " sulphate Potash " dichromate (red chromate i part at a boiling heat, insoluble, insoluble. 60 insoluble, insoluble. i insoluble. Soda r ., " chloride * Table Showing the Composition of the Most Usual Alloys and Solders. Alloys are combinations or mixtures, effected by the fusion of two or more different metals in definite proportions. The electro-plater employs them so constantly that it is important that he be acquainted with the compositions of the most usual alloys, and that he learn the preparation of several of them, which, like the fusible alloys of Darcet, will often be serviceable. It is, of course, possible to vary ad infinitum the mixtures and the proportions of the component metals given in the fol- APPENDIX. 467 lowing table, and thus to arrive at an unlimited number of alloys which, on account of slight differences of color, ductility, sonorousness, etc., have received a great variety of names.* I. Alloys. 55 1 3 24 1-23517 42 1.44338 8 1.07396 26 1.25681 44 1.46807 10 1.09278 28 1.27893 46 1.49314 12 1.11238 30 1.30105 48 I.5l86l H 1.13199 32 1.32417 5 1.54408 16 1.15200 34 1.34729 52 1.57048 18 1.17243 36 1.37082 52.024 1.57079 470 APPENDIX. Table showing the specific gravity of sulphuric acid at 59 F., according to Kolb. Degrees Baum6. 1 Specific gravity. ico parts by weight contain One litre contains in kilogrammes oJ 1 tx Q Specific gravity. ico parts by weight contain One litre contains in kilogrammes S0 3 . H 2 S0 4 . SO 3 . H 2 S0 4 . S0 3 . H 2 SO 4 . SO 3 . H 2 S0 4 . o I. COO 0.7 0.9 0.007 0.009 34 .308 32-8 40.2 0.429 0.526 i 1.007 J -5 1.9 0.015 0.019 35 .320 33.8 41.6 0.447 0-549 2 1.014 2-3 2.8 0.023 0.028 36 332 35-1 43-o 0.468 0-573 3 1.022 3-i 3-8 0.032 0.039 37 345 36.2 444 0.487 0-597 4 1.029 3-9 4.8 0.040 0.049 38 357 37-2 45-5 0.505 0.617 5 1-037 4-7 5.8 0.049 c.o6o 39 37 38.3 46.9 0-525 0.642 6 1.045 5.6 6.8 0.059 0.071 40 383 39.5 48.3 0.546 0.668 7 1.052 6.4 7.8 0.067 0.082 4i 397 40.7 49-8 0.569 0.696 8 1. 060 7.2 8.8 0.076 0.093 42 1.410 41.8 51.2 0.589 0.722 -9 1.067 8.0 9-8 0.085 0.105 43 1.424 42.9 52.8 0.611 0.749 10 1-075 8.8 10.8 0.095 0.116 44 1.438 44.1 54-0 0.634 0.777 ii 1.083 9-7 11.9 0.105 0.129 45 MS 3 45-2 55-4 0.657 0.805 12 I.O9I 10.6 13.0 0.116 0.142 46 1.468 46.4 5 6 -9 0.681 0.835 13 .100 H-5 14.1 0.126 0.155 47 1.483 47.6 58-3 0.706 0.864 H .108 12.4 15.2 0.137 o.i 68 48 1.498 48.7 59.6 0.730 0.893 15 .116 13.2 16.2 0.147 0.181 49 i-SH 49-8 61.0 o-754 0.923 16 .125 14.1 '7-3 0.159 0.195 5 1.530 51.0 62.5 0.780 0.956 '7 .134 *5'* 18.5 0.172 O.2IO 5i 1.540 52.2 64.0 0.807 0.990 18 .142 1 6.0 19.6 0.183 0.224 52 1-563 53-5 65.5 0.836 1.024 19 .152 17.0 20.8 0.196 0.233 53 1.580 54-9 67.0 0.867 1.059 20 .162 1 8.0 22.2 0.209 0.258 54 1-597 56.0 68.6 0.894 1.095 21 .171 19.0 23.3 0.222 0.273 55 1.615 57.i 70.0 0.922 1.131 22 .180 2O.O 24.5 0.236 0.289 5 6 1.634 584 71.6 0-954 1.170 23 .190 21. 1 2.S.8 0.251 0.307 57 1.652 59-7 73-2 0.986 1. 210 24 .200 22.1 27.1 0.265 0.325 58 1.672 61.0 74-7 1.019 1.248 25 .210 23.2 28.4 0.281 0.344 59 1.691 62.4 76.4 1.055 1.292 26 .220 24.2 29.6 0.295 0.361 60 1.711 63.8 78.1 1.092 1.336 27 .231 2 5-3 31.0 0.3II 0.382 61 1-732 65.2 79-o .129 1.384 28 .241 26.3 32.2 0.326 0.400 62 !-753 66.7 81.7 .169 1.432 29 .252 27.3 334 0.342 0.418 63 1-774 68.7 84.1 .219 1.492 30 .263 28.3 34-7 0-357 0.438 64 1.796 70.6 86.5 .268 1-554 3 1 .274 29.4 36.0 0.374 0.459 65 1.819 73-2 89.7 332 1.632 32 .285 30.5 37-4 0.392 0.481 66 1.842 81.6 IOO.O 503 1.842 33 .297 31.7 38.8 0.411 0.503 .APPENDIX. 471 Table of the specific gravity and content of nitric acid, according to Kolb. ri 3 Specific TOO parts con- tain at 32 F. 100 parts con- tain at 59 F. fi Specific loo parts con- tain at 32 F. loo parts con- tain at 59 F. bCrn gravity. * oii ^ gravity. i - HN0 3 . N 2 O 5 . HN0 3 . N 2 S . F HN0 3 . N 2 S . HN0 3 . N 2 5 . o I.OOO o.o O.O O.2 O.I 28 .242 36.2 31.0 38.6 33- 1 i 1.007 I.I 0.9 1.5 1.3 29 .252 37-7 32.3 40.2 34-5 2 I.OI4 2.2 1.9 2.6 2.2 30 .261 39-1 33-5 4L5 35-6 3 1.022 34 2.9 4.0 3-4 31 -275 41.1 35-2 43-5 37-3 4 I.O29 4-5 3-9 4.4 32 .286 42.6 36.5 45' 38.6 5 1.036 5'5 4-7 3 5-4 33 .298 44-4 38.0 47.1 40.4 6 1.044 6.7 5-7 7.6 6.5 34 .309 46.1 39-5 48.6 41.7 7 1.0 5 2 8.0 6.9 9.0 7-7 35 .321 48.0 41.1 50.7 43-5 8 1. 060 9.2 7-9 10.2 8-7 36 334 50.0 42.9 52.9 45-3 9 1.067 10.2 8.7 1 1.4 9.8 37 .346 51.9 44-5 55-o 47.1 10 1-075 II.4 9.8 12.7 10.9 38 359 54-0 46.3 57-3 49.1 ii 1.083 12.6 10.8 14.0 12.0 39 .372 56.2 48.2 59-6 51.1 12 I.O9I 13.8 u.8 15.3 I3.I 40 384 58.4 50.0 61.7 52.9 13 1. 100 15.2 13.0 16.8 14.4 41 .398 60.8 52.1 64-5 55-3 14 1.108 16.4 14.0 1 8.0 15.4 42 .412 63.2 54-2 67.5 57-9 15 1.116 17.6 I 5- 1 19.4 1 6.6 43 .426 66.2 56.7 70.6 60.5 16 1.125 18.9 1 6.2 20.8 17.8 44 .440 69.0 74-4 63-8 l l I.I34 20.2 17-3 22.2 19.0 45 454 72.2 61.9 78.4 67.2 IS I-I43 21.6 18.5 23-6 20.2 46 .470 76.1 65.2 83-0 71.1 19 1.152 22.9 19.6 24.9 21.3 47 485 80.2 68.7 87.1 74-7 20 1.161 24.2 20.7 26.3 22.5 48 .501 84-5 72.4 92.6 79-4 21 1.171 25.7 22.0 2 7 .8 23.8 49 .516 88.4 75.8 96.0 82.3 22 1.180 27.0 23.1 29.2 25.0 49.5 .5.24 90.5 77.6 98.0 84.6 23 .1.190 28.5 24.4 30.7 26.3 49.9 .530 92.2 79.0 1 00.0 85.71 24 1.199 29.8 25-5 32.1 27.5 50.0 .532 92.7 79-5 2 5 i. 210 3M 26.9 33-8 28.9 50.5 .541 95-o 81.4 26 1. 221 33-i 28.4 35-5 30.4 S 1 - } -549 97-3 83.4 27 I.23I 34-6 29.7 37-Q 31.7 5 J -5 -559 1 00.0 85.71 Table showing the specific gravity of sal ammoniac solutions at 66.2 F., according to Schiff. Content of Content of Content of the solution, Specific gravity. the solution, Specific gravity. the solution, Specific gravity. per cent. per cent. per cent. , I.OO29 II 1.0322 21 1. 0606 2 1.0058 12 I-035I 22 1.0633 3 1.0087 13 1.0380 23 1. 0660 4 1.0116 H 1.0409 24 1.0687 5 1.0145 15 1.0438 2 5 1.0714 6 1.0174 16 1.0467 26 1.0741 7 1.0203 17 1.0495 27 1.0768 8 1.0233 18 1.0523 28 1.0794 9 1.0263 19 1.0551 29 1.0820 10 1.0293 20 1.0579 30 1.0846 4/2 APPENDIX. Table showing the electrical resistance of pure copper wire of various diameters. No. of wire, Birmingham wire gauge. Resistance of i foot in ohms. Number of feet required to give resistance of i ohm. No. of wire, Birmingham wire gauge. Resistance of i foot in ohms. Number of feet required to give resistance of i ohm. 0000 0.0000516 19358 17 0.00316 3I6.I 000 0.0000589 16964 18 0.00443 225.5 OO O 0.0000737 O.OOOO922 13562 10857 19 20 0.00603 0.00869 165.7 II5.I I O.OOOII8 8452.6 21 O.OIO4O 96.2 2 0.000132 7575- 1 22 0.01358 73-6 3 0.000159 6300.1 23 0.01703 58.7 4 0.000188 5319.9 24 O.O22CO 45-5 5 0.000220 4545-9 2 5 O.O266I 37-6 6 0.000258 3870.3 26 0.03286 30.4 7 0.000329 3043.4 27 0.04159 24.0 8 0.000391 2557.1 28 0.05432 18.4 9 0.000486 2057.7 29 0.06300 15-9 10 0.000593 1686.5 30 | 0.07393 J 3-5 ii 0.000739 1352.5 3 1 0.10646 9-4 12 0.000896 1 1 1 6.0 32 0.13144 7.6 13 0.001180 847.7 33 0.16634 6.0 H 0.001546 647.0 34 0.21727 4-6 15 0.002053 487.0 35 0.42583 2.4 16 0.002520 396.8 36 0.66537 1-5 Resistance and conductivity of pure copper at different temperatures. Centigrade temperature. Resistance. Conductivity. Centigrade temperature. Resistance. Conductivity. 1. 00000 1. 00000 16 1.06168 .94190 I 1.00381 .99624 17 1.06563 .93841 2 1.00756 .99250 18 1.06959 93494 3 I.OH35 .98878 19 1-07356 .93148 4 I.OI5I5 .98508 20 1.07742 .92814 5 1.01896 .98139 21 1.08164 .92452 6 1.02280 .97771 22 1-08553 .92121 7 1.02663 .97406 23 1.08954 .91782 8 1.03048 .97042 24 1.09365 .91445 9 L03435 .96679 2 5 1.09763 .91110 10 1.03822 .96319 26 1. 10161 .90776 ii 1.04199 9597 27 1.10567 .90443 12 1.04599 95603 28 1.11972 .90113 J 3 1.04990 .95247 29 1.11382 .89784 H 1.05406 .94893 30 1.11782 * .89457 15 L05774 94541 APPENDIX. 473 Table showing actual diameters in decimal parts of an inch corresponding to the numbers of various wire gauges. No. of wire gauge. Roebling. Brown & Sharpe. Birmingham or Stubs. English legal standard. Old English or London. 000000 .46 .464 oocoo 43 432 oooo 393 .46 454 4 454 ooo .362 .40964 425 .372 425 00 331 .3648 .380 348 38 .307 .32495 .340 .324 34 i .283 .2893 3 3 3 2 .263 .257 6 3 .284 .276 .284 3 .244 .22942 259 .252 .259 4 .225 .20431 .238 .232 .238 5 .207 .18194 .22 .212 .22 6 .192 .16202 .203 .192 .203 7 .177 .14428 .18 .176 .18 9 .162 .148 . i 2849 II443 .165 .148 .16 .144 38 10 135 .10189 134 .128 .134 ii .120 .09074 .12 .116 .12 12 .105 .08081 .109 .104 .109 *3 .092 .07196 .095 .092 095 H .08 .06408 .083 .08 .08 3 15 .072 .05706 .072 .072 .072 16 .063 .05082 065 .064 .065 *7 .054 04525 .058 .056 .058 18 .047 .0403 .049 .048 .049 19 .041 .03589 .042 .04 .04 20 035 .03196 .035 .036 035 21 .032 .02846 .032 .032 .0315 22 .028 02534 .028 .028 .0295 23 .025 .02257 .025 .024 .027 24 .023 .0201 .022 .022 .025 2 5 .02 .0179 .02 .02 .023 26 .018 .01594 .018 .018 .O2O5 27 .017 .01419 .016 .0164 .01875 28 .Ol6 .01264 .OI4 .0148 .0165 29 .015 .01125 .013 .0136 OI 55 30 .014 .01002 .OI2 .0124 01375 31 0135 .00893 .010 .0116 .01225 32 .013 .00795 .009 .0108 .01125 33 .Oil .00708 .008 .01 .01025 34 .OI .0063 .007 .OO92 .0095 35 .0095 .00561 .005 .0084 .009 36 .009 .005 .004 .0076 0075 474 APPENDIX. Weight of iron, copper, and brass wire and plates. (Diameters and thickness determined by American gauge.) .No. of gauge. Size of each No. WEIGHT OF WIRE PER 1000 LINEAL FEET. WEIGHT OF PLATES PER SQUARE FOOT. Wro't iron. Steel. Copper. Brass. Wro't iron. Steel. Copper. Brass. at. Inch. Lbs. Lbs. Lbs. Lbs. Lbs. Lbs. Lbs. Lbs. 0000 .46000 560.74 566.03 640.51 605.18 I 7-25 17.48 20.838 19.688 oooT .40964 444.68 448-88 57-95 479.91 15.3615 15-5663 18557 17-533 oo .36480 352-66 355-99 402.83 380.67 13-68 13.8624 16.525 15-613 o .32486 279.67 282.30 3*9-45 301.82 12.1823 I2 -3447 14.716 13.904 I .28930 221.79 223.89 253-34 239-35 10.8488 . 10.9934 13-105 12.382 2 25763 175-89 I 77-55 200.91 189.82 9.6611 9.7899 11.671 11.027 3 .22942 13948 140.80 I 59-3 2 150.52 8.60^3 8.7180 10.393 9.8192 4 .20431 110.62 in. 66 126.35 119.38 7.6616 7-7638 9-2552 8-7445 5 .18194 87.720 88.548 IOO.2O 94.666 6.8228 6.9*37 8.2419 7-787 6 I .16202 .14428 .12849 69-565 55-165 43-75 1 70.221 55-685 44.164 79.462 63.013 49.976 75.075 59-545 47.219 6.0758 5-4105 4.8184 6.1568 5.4826 4.8826 7-3395 6.5359 5.8206 6-9345 6.1752 9 II443 34-699 35.026 i 39.636 37-437 4.2911 4-3483 5-1837 4.8976 10 .10189 27.512 27-772 j 3 J -426 29.687 3.8209 3-8718 4.6156 4-3609 ii .090742 21.820 22.026 24.924 23-549 3.4028 3.4482 4.1106 3-8838 12 .080808 17-304 17.468 19.766 18.676 3-0303 3.0707 3.6606 3.4586 13 .071961 13.722 13-851 I5-674 14.809 2.6985 2-7345 3-2598 3.0799 *4 .064084 10.886 10.989 12.435 11.746 2.4032 2.4352 2.9030 2.7428 15 .057068 8.631 8.712 9-859 9-3I5 2.1401 2.1686 2.5852 2.4425 16 .650820 6.845 6.909 7.819 7-587 1-9058 1.9312 2.3021 2.1751 J 7 045 2 57 5.427 5.478 6.199 1.6971 1.7198 2.0501 1-937 18 .040^03 4-304 4-344 4.916 4 645 I.5II4 i-53 I 5 .8257 1-725 19 .035890 3-4*3 3-445 3.899 3.684 1-3459 1.3638 .6258 20 .031961 2.708 2-734 3.094 2.920 1.1985 1.2145 1.4478 1.3679 21 .028462 2.147 2.167 2.452 2.317 1.0673 1.0816 .2893 1.2182 22 025347 1.719 1-945 1.838 9505 1 .96319 .14*3 1.0849 23 .022571 1.350 1-363 1.542 1-457 .84641 8577 1.0225 .96604 24 .020100 1.071 1.081 1.223 75375 .7638 91053 .86028 25 .017900 0.8491 0.8571 .9699 0.9163 .67125 .6802 .81087 .76612 26 .015941 0.6734 0.6797 .7692 0.7267 59775 .60572 .72208 .68223 2 7 .014195 0.5340 0-539 1 .6099 0.5763 .53231 53941 64303 60755 28 .012641 0.4235 0-4275 .4837 0.4570 4744 .48036 57264 54103 2 9 .011257 0.3358 0-3389 3835 0.3624 .42214 .42777 .50994 .48180 30 .010025 0.2663 0.2688 3042 0.2874 37594 38095 45413 ,42907 31 .008928 0.2113 0.2132 2413 0.2280 .3348 .33926 .40444 .38212 32 -007950 0.1675 0.1691 o.i 808 29813 .3021 .36014 .34026 33 .007080 0.1328 0.1341 .1517 0.1434 2655 .26904 .32072 .30302 34 .006304 0.1053 0.1063 .1204 0.1137 .2364 23955 .28557 .26981 35 .005614 0.08366 0.08445 .0956 0.1015 .21053 21333 2 543i .24028 36 .OO5OOO .06625 .06687 757 .0715 1875 .19 .2265 .2140 37 004453 05255 -05304 .06003 .05671 .16699 .16921 .20172 .19059 38 .003965 .04166 .04205 .04758 .04496 .14869 .15067 .17961 i6973 39 .003531 .03305 .03336 03755 .03566 .13241 .13418 15995 .1511 40 003144 .02620 .02644 .02992 .02827 .1179 .11947 .14242 13456 Specific grav. Weight per cubic foot. 7-7747 185.874 7.847 00-45 8.880 8.386 524-16 7.200 450. 7.296 456- 8.698 543-6 8.218 5I3.6 APPENDIX. 475 Rules for Speed. To find speed of counter-shaft in accordance with main shaft and machine. Subtract the number of revolutions of the main shaft from the number of revolutions the machine should make; divide the remainder by two. The quotient will show the number of revolutions of the counter-shaft. Example. The main shaft runs 200 revolutions per minute, while the machine should run 1000 revolutions per minute. Deduct 200 from 1000, leaving 800, which divide by 2; the quotient will then be 400, which is the number of revolutions the counter-shaft should make. To find diameter of pulley on the main shaft. Multiply the diameter in inches of the receiving pulley of the counter-shaft by the number of revolutions the counter-shaft should make and divide the product by the number of revolutions the main shaft makes. Example. The counter-shaft makes 400 revolutions, the receiving pulley is 7*^ inches in diameter and the main shaft makes 200 revolutions; 400 times 7J^ equals 3000, which divided by 200 equals 1 5 ; this is the diameter in inches of the pulley on the main shaft. To find diameter of pulley on counter- shaft carrying belt to machine. Multiply the number of revolutions the machine should make by the diameter of pulley of the machine and divide by the number of revolutions the counter-shaft makes. Example. Say the machine should make 1000 revolutions, the diameter of pulley on machine being 6 inches, and the counter-shaft making 400 revolutions ; then multiplying 1000 by 6 equals 6000: dividing this by 400 gives 15, which should be the diameter of the pulley carrying belt from counter-shaft to machine. To find the speed* of a machine. Multiply the number of revolutions of the main shaft by the diameter of pulley in inches, and divide by the diameter of receiving pulley of the counter-shaft. The result is the speed of the counter-shaft. Then multiply the number of revolutions of counter-shaft by 4/6 APPENDIX. diameter of transmitting pulley, and divide by diameter of pulley on machine. The result will be the speed of the machine. It should be well understood that no other pulleys but those in contact with one belt should be considered. Comparison of the Scales of the Fahrenheit, Centigrade, and Reaumur Thermometers, and Rules for Converting one Scale into another. These three thermometers are graduated so that the range of temperature between the freezing and boiling points of water is divided by Fahrenheit's scale into 180 (from 32 to 212), by the Centigrade into 100 (from o to 100), and by that of Reaumur into 80 (from o to 80) portions or degress. The spaces occupied by a degree of each scale are consequently as |, \, and \ respectively, or as I, 1.8, and 2.25 ; and the num- ber of degrees denoting the same temperature, by the three scales, when reduced to a common point of departure by sub- tracting 32 from Fahrenheit's, are as 9, 5, and 4. Hence, we derive the following equivalents: A degree of Fahrenheit's is equal to 0.5 of the Centigrade or to 0.4 of Reaumur's; a degree of centigrade is equal to 1.8 of Fahrenheit's or to 0.8 of Reaumur's ; and a degree of Reaumur's is equal to 2.25 of Fahrenheit's, or to 1.25 of the Centigrade. To convert degrees of Fahrenheit into the Centigrade or Reaumur's, subtract 32 and multiply the remainder by f for the centigrade or |- for Reaumur's. To convert degrees of the Centigrade or Reaumur's into Fahrenheit's, multiply the centigrade by -f, or Reaumur's by f , as the case may be, and add 32 to the product. INDEX. A CCUMULATORS, 377, 378 | J\ Acid copper baths, vats for, 104, 105 free, in galvanoplastic baths, determination of, 365, 366 mixtures, recovery of gold from, 318 neutralization of the effect of, 421 potassium carbonate, 438 recovery of, from exhausted dipping baths, 155, 156 vapors, absorbing plant for, 154, 155 Acids, 424-428 organic, salts of the, 446-448 Action, local, 29 Air, renewal of, in plating rooms, 85 Alkalies and alkaline earths, 428, 429 poisoning by, 423 Alkaline earths and alkalies, 428, 429 platinate bath, 320, 321 Alliance machine, the, 78 Alloy containing nickel, deposition of an, 219 Alloys, metallic, for preparing moulds, 389, 390 first deposition of, 6 most usual, and solders, table showing the composition of, 466-469 nickel, deposits of, 219-221 table of, 467 Alternating current machines, 66 currents, 25 Aluminium baths, 348-350 deposition of, 348-352 electro-deposition upon, 350-352 new method for the electro-depo- sition of, 349 potassium sulphate, 440, 441 properties of, 348 American double polishing lathes, 139 Ammeter, 113 Westoti, 102 Ammonia, 429 Ammonium alum, 441 Ammonium chloride, 431 hydrate, 429 phosphate, 446 sulphate, 440 sulphide, 430 Ampere, the, 31 theory or hypothesis of, 11, 12 Amperemeter, 113 Anious, 26 Anode, 26 surface, size of, 183 . wire, 103 coupling the, with the resist- ance boards, voltmeter, shunt and baths, 114 wires, insulation of, 111 Anodes, choice of, 166 for brass bath, 244, 245 copper baths, 231 galvanoplastic baths, 365 nickeling sheet zinc, 208 insoluble, 166, 181 platinum in silvering, 253 nickel, 180-184 reddish tinge of, 184 platinum, 293 proportion of cast, to rolled, 177 silver, 251-260 use of steel plates in place of, 253 suspension of, 107 Antimony and arsenic, deposits of, by contact and immersion, 347, 348 baths, 345, 346 deposition of, 345, 346 -potassium tartrate, 447 properties of, 345 sulphide, 430 - trichloride, 431,432 Antique silvering, 282, 283 Apparatus and instruments, various, 448-453 Aqua fortis, 425 Areas silvering, 259, 260 Armature, 64 Gramme, 67 (477) 478 INDEX. Arsenic and antimony, deposits of, by contact and immersion, 347, 348 baths, 346, 347 deposition of, 346-348 poisoning by, 423 properties of, 346 trisulphide, 431 white, 427 Arseuious acid, 427 addition of, to brass baths, 240 chloride, 432 sulphide, 431 Art-castings, coppered, inlaying of depressions of, 237, 238 Astatic galvanometer, 22 Auric chloride, 434 Australia, gold composition of, 287 Auxiliary apparatus, 93 SACKING, 382 Baking powder, 439 lance, plating, 263-266 Bath, bright dipping, 152, 275 conditions required to guarantee good performance, 167 electrolytic, requisites of a, 162 working the, with the electric current, 165 Baths, acid copper, vats for, 104, 105 agitation of, 162-164 aluminium, 348-350 antimony, 345, 346 arsenic, 346, 347 brass, 238-243 bronze, 247,248 cobalt, 222 concentration of, 161 conclusion as to the condition of, from changes in the specific gravity, 161,162 containing potassium cyanide, holders for, 105 filtering of, 166 for gilding by contact, 305, 306 dipping, 308-310 gold, 288-293 heating of, 86, 87 lead, 338 nickel, vats for, 104, 105 palladium, 325 platinum, 319-322 steel, 341-344 temperature of, 162 tin, 327-329 to secure lasting qualities to, 166 vats for heating, 105 Batteries, bichromate, 53-57 Batteries, plunge, 53-57 storage, electro-chemical process of forming, 378 Battery, copper-bath for galvano- plastic depositions with the, 362 Foote's pinnacle gravity, 43, 44 galvanoplastic depositions with the, 360, 361 reduction of metals without a, 168, 169 Stoehrer's, 56 stripping nickeled articles by the, 196 trough, 2, 32 Baume's hydrometer, 450 Beardslee, G. W., cobalt solution recommended by, 223 Becquerel's element, 35 Bell metal, 238 Bells, coloring of, 341 Belt strapping attachment or endless belt machine, 142, 143 Benzine, removal of grease with, 156, 157 Bertrand, aluminium bath according to, 348 palladium bath according to, 325 Bicarbonate of potash, 438 Bichromate batteries, 53-57 Bicycles, nickeling parts of, 186 Binding posts, 107 screws, 107 Bird, production of the amalgams of potassium and sodium by, 4 Black color on copper, 405 lead, gilt, 373 mixture of, with bronze powder, 373, 374 silvered, 373 -leading, 372 machine, 372 wet process of, 372 lustrous on iron, 414, 415 nickeling, 344 on zinc, 413 sulphide of antimony, 430 Blue on iron, 416 steel, 416 black on copper, 405 zinc, 413 gray shades on copper, 405 vitriol, 441, 442 pure, table of approximate content of, at different de- grees Be., and at 59 F., 358 Bobs, cloth, 137 construction of, 200, 201 polishing, 137 INDEX. 479 Boettger on the deposition of nickel from its double salts, 6 platinum bath of, 319 steel bath according to, 341, 342 tinning solution according to, 332 Boiling, nickeling by, 217-219 pans, 164, 165 tinning by, 330, 331 Boracic acid, 426, 427 Boric acid, 426, 427 as addition to nickeling baths, 171, 172 Bossard Mechano - Electroplating tanks, 455-461 Bouant's method of amalgamating zinc, 34 Brandley, directions by, for preparing gelatine moulds, 397 plating balance used by, 263-266 Brass and bronzes, coloring of, 408-412 articles, cobalting, 223, 224 small, tinning solution for, 331,332 superficial coating of tin on, 333 bath, constitution of a, 238, 239 formation of slime on the anodes in the, 245 regulation of a, 245, 246 ' with cuproso-cupric sulphite, 241 baths, 238-243 anodes for, 244, 245 density of current for, 243 irregular working of, 240 bronze and copper, deposition of, 225-248 brown color called bronze Barbe- dienne on, 410 casting of, with zinc, 337 castings, grinding of, 136 coloring of, 347 color resembling gold on, 409, 410 corn-flower blue on, 411 deposits, polishing of, 149 Ebermayer's experiments in col- oring, 411, 412 gray color with a bluish tint on, 409 lustrous black on, 408 nickel bath for, 178 nielling upon. 282 objects, dead or dull surface on, 153 tinning of, 327 pale gold color on, 409 pickling of, 151,152 production of a grained surface on, by pickling, 156 Brass, properties of, 238 red, 238 removal of oxide from, 158 scratch brushes for, 146 sheet, nickeling, 209 sheets, polishing of, 136 steel gray on, 408, 409 straw color, to brown, through golden yellow, and tornbac color on, 409 various colors upon, 407, 408 violet on, 411 wire and plates, weights of, 474 yellow, 238 Brassed articles, inlaying of, 247 Brassing, 238-247 by contact and dipping, 247 color of, 244 distance of objects in, from' the anodes, 246 execution of, 243-247 sheet zinc, 206 unground iron castings, 246, 247 Bright dipping bath, 152 Platinum Plating Co., of London, platinum bath, patented by, 320 Britannia, preparation of, for silver- ing, 268-270 removal of oxide from, 158 Bronze articles, clay yellow to dark brown on, 410 dead yellow on, 410 Barbdienne on brass, 410 baths, 247, 248 brass and copper, deposition of, 225-248 -like patina on tin, 416 nickeling of, 151 , 152 removal of oxide from, 158 Bronzes, 238 and brass, coloring of, 408-412 Bronzing, 247, 248 execution of, 248 on zinc, 413, 414 Brown black with bronze lustre on iron, 416 color called bronze Barbddienne on brass, 410 on copper, 404, 405 Bruce, addition of bisulphide of car- bon to nickel baths, recommended by, 179 Brugnatelli, first practical results in electro-gilding attained by, 3 Brush coppering, 236, 237 dynamo, 70-72 Brushes, 126 collecting, 64 480 INDEX. Bunsen element, 37-40 elements for galvanoplastic de- positions, 360, 361 location of, 86 manipulation of, 42, 43 plunge battery, 53 Burning, 187 Burnishers, 149 Burnishing, 144, 145 machines, 267 operation of, 149, 267 Busts, galvanoplastic reproduction of, 388, 389 Butter of antimony, 431 , 432 zinc, 432, 433 /CALCIUM carbonate, 439 I, hydrate, 429 California gold, composition of, 287 Capsules or evaporating dishes, 448 Carbonates, 438-440 Carbon, bisulphide of, addition of, to nickel baths, 179 disulphide or bisulphide, 430 Carboy rocker, 158, 159 Carlisle and Nicholson, decomposi- tion of water by, 3 Cast-iron, bath for brassing, 242 coating with bronze, 247 objects, pickling of, 150, 151 tinning of, 328 zinc bath for, 335 Casts, plaster of Paris for, 390-393 Cathode, 26 Cations, 26 Caustic potash, 428 soda, 428 Cell apparatus, 354-358 copper bath for the, 358 galvanoplastic depo- sition in the, 354- 359 Cellulose lacquers and varnishes, 417- 419 Centigrade, Reaumur and Fahrenheit thermometers, comparison of the scales of the, and rules for convert- ing one scale into another, 476 Chain, galvanic, 16 Chalk, 439 Check voltmeter, 454 Chemical and electro-chemical equiv- alents, table of, 462, 463 products and various apparatus and instruments used in electro- plating, 424-453 Chemicals, purity of, 160 Chile saltpetre, 444 Chloride of silver, reduction of, 286 Chlorine combinations, 431-435 poisoning by, 423, 424 Christofle & Co., experiments by, with magneto-electrical machines, 7,8 Chromes, metallic, 339-341 Chromic acid, 427, 428 Chromium combination, soluble, 41 Circuit, closing, 16 Citric acid, 426 Clamond's thermo-electric pile, 58, 59 Clarke, electric generator produced by, 65 Clausius's theory of molecules, 26, 27 Clay, metallization of, 400 cells, filling of, 375, 376 Cleansing apparatus, 108 Cliches, cell apparatus for producing, 355, 356 nickeling, 214-216 Closing circuit, 16 Cloth bobs, 137 Cobalt-ammonium sulphate, 443 and nickel, deposition of, 169-225 baths, 222 carbonate, 440 chloride, 433 properties of, 221 sulphate, 443 Cobalting, 221-225 articles en masse, 223 by contact, 224, 225 small fancy articles, bath for, 223, 224 Coins, taking casts from, 390, 391 Colcothar, 144 Cold gilding, bath for, 289, 290 Collecting brushes, the, 64 Collector, the, 64 Coloring brass and bronzes. 408-412 Bbermayer's experi- ments in, 411, 412 iron, 414-416 patmizing, oxidizing of metals, 403-417 silver, 417 tin, 416 zinc, 413, 414 Common salt, 431 Commutator, the, 64 cylinder, 64 Compress polishing wheels, 137, 138 Conducting rods, arrangement of, 106, 107 fixing of, on vats, 105, 106 INDEX. 481 Conducting salts, 171 wires, 103 calculating the thickness of, 120, 121 Conductor, development of heat in the, 29 resistance of a, 17 Conductors, bad, 13 good, 13 Contact, brassing by, 247 cobalting by, 224, 225 coppering by, 235, 236 deposits of antimony and arsenic by, 347, 348 electricity, discovery of, 1 electro-deposition by, 108, 169 gilding by, 305-308 immersion and friction, gilding by, 305-312 leading by, 339 nickeling by, 217-219 platinizing by, 324 silvering by, 271-277 steeling by, 345 tinning by, 330, 331 zincking iron by, 337 Continuous current machines, (56 Copper acetate, 447 -alloys, current for nickeling, 188 dead or dull surface on, 153 silvering articles of, 275, 276 articles, cobalting, 223. 224 small, tinning solution for, 331,332 stripping of, 316 superficial coating of tin on, 333 bath, Delval's, 351 for the cell apparatus, 358 removal of acid from, 359 with cupron, 229 sulphate of copper, 228, 229 baths, 225-231 anodes for, 231 for galvanoplastic deposi- tions with a separate source of current, 361-365 phenomena appearing in, 231,232 vats for, 231 with cuproso-cupric sulphite, 229 without potassium cyanide, 229, 230 black color on, 405 blue-black color on, 405 blue-gray shades on, 405 31 Copper, brass and bronze, deposition of, 225-248 bronzing of, 405 brown color on, 404, 405 carbonate, 439 castings, grinding of, 136 chemically pure, 352 chloride, 432 coating black leaded surfaces with, 373 grasses, leaves and flowers with, 399 laces and tissues with, 398 mercury vessels of thermom- eters with, 400 of, with zinc, 337 wood with a galvanoplastic deposit of, 399. 400 wooden handles of surgical instruments with, 400 coloring of, 347, 403-408 current for nickeling, 188 cyanides, 436, 437 dark steel-gray color on, 407 dead black on, 4()o, 406 deep black color on, 406 deposited by electrolysis, physi- cal properties of, 352 deposits, polishing of, 149 determination of content of, in galvanoplastic baths, 366, 367 determination of content of, re- quired for a beautiful red gold, 299 determination of quantity of, dis- solved in stripping cobalted copper plates, 222, 223 for galvanoplastic purposes, 352, 353 galvanoplastic depositions, elas- ticity, strength and hardness of, 362 Hiibl's experiments with, 353 massive, various colors upon, 407. 408 nickel bath for, 178 objects, tinning of, 327 pale red of copper color to dark chestnut-brown on, 403, 404 pickling of, 151, 152 plates, facing of, with cobalt, 222 polishing of, 136 printing plates, galvanoplastic bath for, 362 steeling of, 342, 343 properties of, 225 pure, resistance and conductivity of, 472 482 INDEX. Copper, red brown color on, 405 reduction of, from its solution by iron, early knowledge of, 1 removal of oxide from, 158 salts, poisoning by, 423 scratch brushes for, 146 sheet, nickeling, 209 silvering of, early knowledge of, 1 Smee's experiments with, 353 steel-gray color on, 407 sulphate, 441,442 solutions, different, table of specific elec- trical resistances of, at various tempera- tures, 464 to coat zinc plates with a very thin, but hard layer of, 236 wire and plates, weights of, 474 fine, silvering of, 280 pure, table of the electrical resistance of, 472 -zinc alloy, solution for trans- ferring, 242, 243 Coppered art-castings, inlaying de- pressions of, 237, 238 articles, bronzing of, 405 coating of, with another metal, 235 turning white of, 234, 235 Coppering, 225-238 by contact and dipping, 235, 236 cleansing of articles previous to, 232, 233 defective places in, 233 execution of, 231-235 needles' eyes, 237 sheet zinc, 206, 207 small articles, en masse, 235 dark, round stains in, 233, 234 steel pens, 237 Cork, gilding with the, 310-312 Corn-flower blue on brass, 411 Corvin's niello, 398, 399 Coulomb, law of, 15 the, 31 Counter current, 27 currents, 191, 192 -shaft, to find speed of, in accord ance with main shaft and ma- chine, 475 Cream of tartar, 446 Crucibles, 449 Cruikshank's investigations, 3 trough battery, 2 Cubic nitre, 444 Cuivre fume, 405 Cuivre poli deposit, 238-247 Cupric sulphate, 441 , 442 Cupron, copper bath with, 229 element, 50 Cuproso-cupric sulphite, brass bath with, 241 copper baths with, 229 Cuprous sulphite, 442 Cups, gilding the inner surfaces of, 297 Current, counter, 27, 191, 192 electric, chemical actions of the, 25-31 extra, 25 galvanic, 16 hydro-electric, 16 induced, 24 inductive, 24 polarizing, 27, 192 primary, 24 quantity for the correct formation of the deposit, 91, 92 of, 17-21 coupling elements for, 20 regulator, 93, 94 secondary, 24 sources of, 32-84 volumes, table of the value of equal, as expressed in amperes per square decimetre, per square foot and per square inch of electrode surface, 463, 464 Currents, alternating, 25 Cutlery, cleansing of, 269 Cyanides, 4o5-438 poisoning by, 422, 423 DANIELS element, 35, 36 for galvanoplastic depositions, 360 Dark steel gray color on copper, 407 Daub, R., cobalt bath recommended by, 223, '224 Davy, Sir H., discovery of potassium and sodium by, 3 Dead black on copper, 405, 406 gilding, 299-301 Deep black color on copper, 406 Delval, copper bath recommended by, 351 Deposit, cuivre poli, 238-247 detaching the, from the mould, 380 formation of the, 122, 123 or shell, backing the, 380-382 penetration of the, into the basis- metal, 167 Deposition, first requisite for, 91 INDEX. 483 Deposition of antimony, arsenic and aluminium, 345-352 cobalt, 221-225 copper, brass and bronze, 225-248 gold, 287-318 nickel, 169-221 nickel and cobalt, 169- 225 platinum and palla- dium, 318-326. silver, 249-287 tin, zinc, lead and iron, 326-345 Deposits of iridium and rhodium, 326 De Ruolz, first deposition of metallic alloys by, 6 labors of, 5 Dip, preparation of, 153 Dipping, 109 basket, 193 baths, exhausted, recovery of acid and metal from, 155, 156 for gilding by, 308-310 brassing by, 247 coppering by, 235, 236 Du Fresne s method of fire-gilding,315 Dun's potash element, 51, 52 Dupre's solution for filling the ele- ments, 40 Dynamo, best mode of setting the, in motion, 110 Brush, 70-72 copper bath for galvanoplastic depositions with the, 362 -electric machine, definition of a, 64 parts of a, 64 machines, arrangements with, 109-121 various, 8, 9 evolution of, in the United States, 77-84 Fein's, 70 -generator, parts of a, 64 Gramme, 66, 67 disadvantage of, 68, 69 Krottlinger, 74. 75 I/ahmeyer, 75-77 "Little Wonder," 78 machines, 66 galvanoplastic depositions with the, 361-367 modern Gramme, 67, 68 most suitable, data for, 84 rules for setting up a, 109, 110 Schuckert's flat ring, 69, 70 Siemens & Halske, 72-74 Dynamo, stripping nickeled articles with the, 196 transition of the magneto-electric machine to the, 65 "Wonder," 78,79 Dynamos manufactured by the Han- son & Van Winkle Co., 77-84 Dyne, 30 T^BERMAYER, experiments of, in JJ, coloring brass, 411, 412 , silver-immersion bath, accord- ing to, 274 Electric connection gripper, 374, 375 induction, discovery of, 4 units, 30 Electrical current, chemical actions of the, 25-31 potential, 16 Electricities, attraction and repulsion of, 13 Electricity, 12-21 and magnetism, 10-31 double fluid hypothesis of, 14 Herz's investigations of the na- ture of, 15 kinds of, 13 negative, 13 positive, 13 resinous, 13 single fluid hypothesis of, 14 vitreous, 13 Electro-chemical and chemical equiv- alents, table of, 462, 463 equivalents, 29, 30 processes, prominent in- vestigators and practi- tioners of, 9 Storage Battery Co., plant installed by the, 378-380 -chrorny, 339-341 -deposition by contact, 168, 169 combination of fire-gilding with, 314, 315 imitation of niel by, 282 processes of, 159-169 upon aluminium, 350-352 -etching, 385-387 -gilder, brush employed by the, 126 -gilding, first practical results at- tained in, 3 -magnetic induction machine, first, construction of, 4 -magnetism, 21-23 -magnets, 23 -metallurgy, historical review of, 1-9 4 8 4 INDEX. Electro-motive force, 16 of elements, table of, 465 series of, 15 tension, series of, 15 -plating arrangements in partic- ular, 89-121 chemical products and vari- ous apparatus and instru- ments used in, 424-453 establishment, ground plan of an, 116-120 establishments, arrangement of, in general, 85-1 2l plant, parts of a, 89 Electrodes, 26 Electrolysis, 25-31 decomposition of water by, 3 Electrolyte, 26 Electrolytic laws discovered by Fara- day, 27-29 Electropoion, 40 Electrotypes in iron, bath for the production of, 342 finishing, 382-385 nickeling, 214-216 Element, Becquerel's, 35 Bunsen, 37-40 cupron, 50 Daniell's, 35, 36 Dun's potash, 51. 52 galvanic, 16 Grove's, 37 Knaffe and Kiefer's, 52 Lallande and Chaperon, 48-50 Leclanche, 48 Meidinger, 36. 37 Oppermanu's, 44-48 Smee's, 34, 35 Elements, arrangement with, 89-109 Buusen, location of, 86 manipulation of, 42, 43 constant, 35 coupling of, 19,'20 for electro motive force or tension, 20 quantity of current, 20 determination of the number of, required for plating, 90, 91 Dupre's solution for filling the, 40 galvanic, o2-57 mixed coupling of, 20 soluble chromium combination for, 41 table of the electro-motive force of, 465 various, 51 Elements, with their symbols, atomic weights and specific gravities, table of, 461 Elkington establishment, Birming- ham, arrangement in the, for agitating the silver bath, 257 observations of, 258 Elkingtons, labors of the, 5 Eisner's bronze bath, 247 tinning bath, 332 Endless belt machine or belt strap- ping attachment, 142, 143 Emery, grades of, 132 Etching ground, 386 Evaporating dishes or capsules, 448 Exhaust tumbling barrel, 129, 130 Eyes, silvering of, 275 tinning solution for, 331, 332 PAHRENHEIT, Centigrade and JP Reaumur thermometers, com- parison of the scales of the, and rules for converting one scale into another, 476 Faraday, discovery of electric induc- tion by, 4 electrolv tic laws discovered by, 27-29 Farad, the, 31 Fein's bichromate battery, 53, 54 dynamo, 70 Ferric oxide, 144 sulphide, 431 Ferrous sulphate, 441 Fibre brushes, 135 Fibres, 135 Field, magnetic, 12 magnets, the, 64 Filtering material, 451 Filters, 451, 452 Fine wheel, 132 Fire gilder, brush employed by the, 126 gilding, combination of, with electro-deposition, 314, 315 or mercury gilding, 312-315 Flasks and glass balloons, 448 Flexible shaft, 143, 144 Floors of plating rooms, best material for, 87 Flowers coating of, with copper, 399 Force, lines of, 63 or power, 30 region of the lines of, 63 Foote s pinnacle gravity battery, 43, 44 Foot lathe, 137-139 Forks, deposit of silver on, 262 INDEX. 485 Forks, extra heavy coating of silver on the convex surfaces of, 270 slinging wires for, 262 French form of cell apparatus, 357 Friction, contact and immersion, gild- ing by, 305-312 gilding by, 310-312 Frosting, swing brushes for, 123 /^AIFFE, recommendation by, 222 VjT Galvani, discovery of contact electricity by, 1 experiments of, 1,2 Galvanic chain, 10 current, 1(5 element, 1G elements, 32-57 .Galvanometer, astatic, 22 first construction of the, 4 horizontal, 95 indications by the, 97-100 sine, 22 tangent, 22 vertical, 95 Galvanometers, 22 Galvauoplastic baths, agitation of, 362-865 anodes for, 365 determination of content of cop- per in, 366, 367 determination of free acid in, 365, 366 deposit, current strength for, 376, 377 deposition by the battery and dynamo machine, 359- 367 in the cell apparatus, 354-359 depositions, copper baths for, with a separate source of current, 361-365 of copper, elasticity, strength and hardness of, 362 method for originals in high re- lief, 396 operations in iron, 400, 401 nickel, 401, 402 silver and gold, 402, 403 operator, pencils and brushes used by the, 126 process, invention of the, 4 reproduction of busts, vases, etc., 388, 389 Galvanoplasty, 352-403 definition of, 352 processes used in, 353 special uses of, 397-400 Galvanoscope, first construction of the, 4 Galvanoscopes, 22 Gas carbon anodes, 182 Gassiot, plan to obtain metallo- chromes, recommended by, 340,341 Gauduin's copper bath, 231 Gauze, metallic, gilding of, 303, 304 Gelatine moulds, 396, 397 German form of cell apparatus, 357, 358 silver articles, stripping of, 316 deposit of, 220, 221 pickling of, 151, 152 polishing of, 136 preparation of, for silvering, 269 removal of oxide from, 158 Germany, process for the determina- tion of genuine silvering in use by custom-bouse officers in, 285 Gilded articles, beautiful rich appear- ance of, 302 matt for, 308 removing gold from, 315, 316 stripping, 315, 316 Gilder of watch works, brush used bv the, 126 Gilding, bichromate element for, 55 by contact, 305-3(18 immersion, and by fric- tion, 305-312 dipping, baths for, 308-310 friction, 310-312 weight, 297 cold, bath for, 289, 290 coloring of, 301 . 302 current-strength for, 296, 297 dead, 299-301 defective, treatment of, 308 execution of, 295-298 fire or mercury, 312-315 genuine, determination of, 316, 317 glass, 310 green, 299 hot, bath for, 291 improving bad tones of, 302 in the cold bath, process of, 297 porcelain, 310 preparation of articles for, 296 red, 298, 299 rose-color, 299 486 INDEX. Gilding, wax, 301. 302 with the cork. 310-312 hot bath, 297, 298 rag, 310-312 thumb, 310-312 without a battery, 295, 296 Glass balloons and flasks, 448 gilding, 310 jars, 448, 449 metallization of, 400 platinizing, 324 Glauber's salt, 440 Glue pot, 141, 142 Gold amalgam, preparation of, 312 bath, determination of the con- tent of copper in a, for a beautiful red gold, 299 with yellow prussiate of potash, 290, 291 baths, 288-293 management of, 293-295 preparation of, with the assist- ance of the electric current, 292 recovery of gold from, 317, 318 small, porcelain dish for, 294. 295 baths, vats for, 294 burnt, 300 chloride, 434 color, pale, on brass, 409 resembling, on brass, 409, 410 deposit, coloring of the, 293, 294 redder color on, 301, 302 deposition of, 287-318 deposits, polishing, 149, 298 galvanoplastic operations in, 402, 403 incrustations with, 281 , 303 native, analyses of, 287 occurrence of, 287 porcelain capsules for dissolving, 306, 307 properties of, 287, 288 recovery of, from gold baths, 317,318 removing, from gilded articles, 315, 316 scratch brushes for, 146 solder, table of, 469 varnishers, operation of, 419, 420 -workers, bichromate element for temporary use by, 55 Gore, brass bath recommended by, 242 experiments of, 167 Gountier's bronze bath, 247 Goze's process for obtaining a deposit of aluminium, 348, 349 Grained surface, production of a, by pickling, 156 Graining, 277-280 operation of, 279, 280 preparations used for, 278, 279 Gramme's machine, 8, 60, 67 Grasses, coating of, with copper, 399 Gray on zinc, 413 with a bluish tint on brass, 409 Grease, freeing the objects from, 108, 109 removal of, 156-158 table for freeing articles from, 118,119 Green gilding, 299 vitriol, 441 Grinding, 132, 133 disks, construction of, 132 treatment of, 133 execution of, 134 flexible shaft for, 143, 144 lathes, 133, 134 rooms, 88 Gripper, electro-connection, 374, 375 Grove's element, 37 Giilcher's thermo electric pile, 60-62 Gun-barrels, browning of, 347, 414 coating of, with lead, 339 metal, 238 Gutta-percha, introduction of, 5 moulding in, 367-369 softening, 368 HAEN, determination of content of copper in galvanoplastic baths, according to, 366, 367 Hanson & Van Winkle Co., dynamos manufac- tured by the, 77-84 lathe manu- factured by the, 139, 141 plating room arranged by the, 120 Hard solder, table of, 468 Hassauer's copper bath, 226. Hauck's thermo-electric pile, 59, 60 Heat, development of, in the conduc- tor, 29 Hefner-Alteneck's machine, 8 Heliography, 387, 388 Herz, Prof., investigations of, 15 Hess, bath of, for deposits of tombac, 248 solution for transferring any cop- INDEX. UNIVEBSTT 487 per-zinc alloy, according to, 242, 243 Hoe & Co., electro-connection gripper of, 374, 375 Hollow-ware, Britannia, preparation of, for silvering, 269, 270 gilding the inner surfaces of, 297 Holmes type of machine, 7, 8 Hooks, silvering of, 275 tinning solution for, 331, 332 Horn silver, 433, 434 Horse-power, English, 31 French, 31 Hot gilding, bath for, 291 Hiibl, experiments of, on the elastic- ity, strength and hardness of galvano- plastic deposi- tions of cop- per, 362 with galvano- plastic baths at rest or in motion, 362, 363 with copper, 353 Hydraulic press, 369, 370 Hydrochlorate of zinc, 432, 433 Hydrochloric acid, 425, 426 Hydrocyanate of silver, 437 zinc, 437 Hydrocyanic acid, 426 poisoning by, 422, 423 Hydro-electric current, 16 Hydrofluoric acid, 428 Hydrometers, 449-451 Hydroplatinic chloride, 434, 435 Hydrosulphate of ammonia, 430 Hydrosulphuric acid, 429, 430 Hygienic rules for the workshop, 421-424 Hyponitric gases, poisoning by, 423, 424 TDIO-ELECTRICS, 13 Immersion, contact and friction, gilding by, 305-312 deposits of antimony and ar- senic by, 347. 348 silvering by, 271-277 tinning by, 330 Incrustations with gold, 303 silver, gold, and other metals, 281 Induced current, 24 Induction, 23-25 Induction, electric, discovery of, 4 Inductive current, 24 Inductor ring, cleaning of the, 110,111 Inlaying brassed articles, 247 depressions of coppered art cast- ings, 237, 238 Instruments and apparatus, various, 448-453 sharp surgical, nickeling, 213, 214 surgical, coating wooden handles of, with copper, 400 Ions, 26 Iridescent colors, production of, 339- 341 Iridium, deposits of, 326 Iron-ammonium sulphate, 441 articles, brightening of, 131 coating of, with lead, 339 grinding of, 135, 136 superficial coating of tin on, ooo tinning solution for, 331 bath for brassing, 241 baths, management of, 344 blue on, 416 brown black with bronze lustre on, 416 cast, bath for brassing, 242 coating with bronze, 247 tinning of, 328 zinc bath for, 335 castings, unground, brassing of, 246, 247 coloring, 414-416 copper baths for, 226, 227 coppering of, previous to nickel- ing, 185, 186 current for nickeling, 188 deep black deposit on, 343, 344 deposition of, 341-345 electrotypes in, bath for the pro- duction of, 342 galvanoplastic operations in, 400, 401 lustrous black on, 414, 415 nickel bath for, 178 objects, brassed, bronze Barbe- dienne on, 410 objects, removal of oxide from, 158 ore, magnetic, 10 pickle for, 151 protosulphate, 441 -sheet, nickeling, 209, 210 silvering of, early knowledge of, 1 silvery appearance with high lustre on, 416 sulphate, 441 wire and plates, weights of, 474 488 INDEX. Iron, wrought, bath for brassing, 242 coating with bronze, 247 zinc bath for, 335 zinckiug of, by contact, 337 ACOBY, Prof., invention of the galvanoplastic process by, 4. 5 Joule's experiments, 1:9 J KAISER, R., deposition of an alloy containing nickel according to, 219 Kaselowsky's nickel bath, 176 Keiser & Schmidt's bichromate bat- tery, 54 Kettles, 164. lf>5 Klein, steel bath recommended by, 342 Knaffe and Kiefer's element, 52 Knife blades, nickeling, 213, 214 Knight, S. P., wet process of black leading invented by, 372 Knives, deposit of silver on, 262 Kristaline, 418 Krottlinger dynamo, 74, 75 T ACES, coating of, with copper, 398 \^f Lacquer similar to zapon, prep aration of, 418, 419 Lacquering, 417-420 Lacquers and varnishes, cellulose, 417-419 Lahmeyer dynamo, 75-77 Lallande and Chaperon element, 48- 50 Lamp-feet of cast-zinc, nickeling of, 190, 191 legs, brassed, coloring gray, 346 Lang & Son, patent of for nickeling wire gauze 212. 213 Langbein Dr. G., plunge battery manufactured by, 56, 57 Lathe brush, 147, 148 foot, 137, 138, 139 manufactured by the Hanson & Van Winkle Co., 139, 141 Lathes, American double polishing, 139 grinding, 133, 134 Law, Coulomb's, 15 Ohm's, 4, 17, 18 Laws, electrolytic, discovered by Far- aday, 27-29 Lead acetate, 447, 448 baths, 338 deposition of, 338-341 properties of, 338 removal of oxide from, 158 salts, poisoning by, 423 Leading by contact, 339 Leather, plates for the production of imitations of, 399 Leaves, coating of, with copper, 399 Leclanche element, 48 Lenoir's process galvanoplastic method for originals in high relief, 396 Lime, burnt or quick, 429 mixture preparation of, 157 neutralization of the effect of, 421 Line, neutral, 10 Lines of force, 63 " Little Wonder " dynamo, 78 Liver of sulphur, 430 Loadstone, 10 London Metallurgical Co., areas sil- vering patented by, 259 Liidersdorff, solution for coppering by contact given by, 2^5, 236 Lunar caustic, 445, 446 Lustrous black on brass, 408 Lyes, caustic, neutralization of the effect of, 421 MACHINE, to find the speed of a, 475, 476 Magnetic field, 12, 63 iron ore, 10 meridian, 11 needle, deflection of the, by the electric current, 3 rule for the determination of the direction of the, to the conducting wire, 21 poles, 10 Magnetism, 10-12 Ampere's theory or hypothesis of, 11, 12 and electricity, 10-31 Magneto- and d\ namo-electric ma- chines, 62-84 -electric machine, transition of the, to the dynamo, 65 machines, 66 Manduit, bronzing copper and cop- pered articles according to, 405 Manne. c mann Pipe Works, process of the, for electro-deposition upon aluminium, 352 Marble, 4h9 Martin and Peyraud, method of gild- ing by friction, described by, 311, 312 Matrices in plastic material, prepara- tion of, 367-371 Medals, cell apparatus for moulding, 355 INDEX. 489 Medals, taking casts from, 390, 391 Medium wheel, 132 Meidinger element, 36, 37 Mercuric nitrate, 445 Mercurous nitrate, 444, 445 Mercury or fire gilding, 312-315 salts, poisoning by, 423 Meriden Britannia Co. , practice of the, in preparing ar- ticles for silver- ing, 208, 269 solution for silver plating used by the, 270 striking solution of the, 270 Meridian, magnetic, 11 Meritens, bright black color on iron I according to, 415 Metal, recovery of, from exhausted dipping baths, 155, 156 white, preparation of, for silver- ing, 268, 269 Metallic articles, chemical treatment of, 150-159 mechanical treatment of, 122-150 treatment of, 122-159 before elec- tro plating, 122-145 during and after the electroplat- ing process, 145-150 chromes, 330-341 to}S, metallo chromy for orna- menting, 341 wire and gauze, gilding of, 303- 305 Metallization by metallic powders, 395 the wet way, 393-395 Metals, coloring, patiniziug, oxidiz- ing of, 403-417 conductivity of, 17 incrustations with, 281 reduction of, without a battery, 168, 169 table of melting points of some, 469 Moire", metallique, 326 Molecules, Clausius's theory of, 26, 27 Monopotassic carbonate, 438 Montgomery, Dr., introduction by, of gutta-percha, 5 Mould, detaching the deposit from the, 380 Moulding in gutta-percha, 367-369 plaster of Paris, 391, 392 in wax, 370, 371 Moulds, gelatine, 396. 397 in plastic material, preparation of, 367-371 metallic alloys for preparing, 389, 390 metallizing of, by the wet way t 393-395 metallization of, by metallic pow- ders, 895 suspension of, in the bath, 375 Multipliers, 22 Muriate of gold, 434 zinc, 432, 433 Muriatic acid, 425, 426 Murray, discovery by, of making non- metallic surfaces conductive, 5 \TATURE-PRINTING, 397. 398 |\ Needles' e)es, coppering, 237 tinning of, 332. 333 Nees, Prof., process of, for electro- deposition upon aluminium, 351,352 Negative wire, 103 Neutral line, 10 zone, 10 Nicholson and Carlisle, decomposi- tion of water by, 3 Nickel alloys, deposits of, 219-221 -ammonium sulphate, 443 and cobalt, deposition of, 169-225 anodes, 180-184 reddish tinge of, 184 rolled, 183 articles, preparation of, for silver- ing, 269 bath, alkaline, testing of, 184 electro itotive force required for a, 90 English, formula for, 179 for rough or polished cast- ings, 179 small articles, 179 . very thick deposits, 179, 180 most simple, 173 neutral, 172 suspension of articles in the, 186 without nickel salt, 180 baths, 170-180 addition of bisulphide of car- bon to, 179 anodes for, 181 containing boric acid, 175-177 current strength for, 186, 187 490 INDEX. Nickel baths, determination of acidity and alkalinity of, 172, 173 for special purposes, 178, 179 freshly prepared, working of, 180 old, recovery of nickel from, 216, 217 preparation of, 165 refreshing, 198, 199 use of carbon anodes in, 182 rolled and cast anodes in, 183 vats for, 104, 105 bronze, 220 carbonate, 440 chemical equivalent of, 170 chloride, 433 -copper-tin alloy, bath for depos- iting, 220 -zinc alloy, solution for de- positing, 220 deposition of, 169-221 from its double salt, 6 deposits, dead, 199 polishing, 149, 199 galvanoplastic operations in, 401, 402 harder and more brittle, deposi- tion of, 172 patent for the deposition of, 6 properties of, 169, 170 recovery of, from old baths, 216, 217 scratch brushes for, 146 silver, preparation of, for silver- ing, 269 sulphate, 442, 443 various colors upon, 407, 408 very thick deposits of, 189 Nickeled articles, stripping of, 194-196 objects, removal of moisture from, 148 Nickeling, additional rules for, 191 bath, slightly acid reaction of, 171 baths, additions to, 171, 172 black, 344 brass sheet, 209 by contact and boiling, 217-219 change of color of, 197 copper sheet, 209 criteria for judging the correct progress of, 187, 188 dark, or spotted, or marbled, 196, 197 defective, to improve, 217 discolored, 196 electrotypes, cliches, etc., 214- 216 Nickeling, en masse of small and cheap objects, 193, 194 knife blades, sharp surgical in- struments, etc., 213, 214 partial, cause of, 190 peeling of, in scratch-brushing, 197 polarizing phenomena in, 191-193 process of, 184-193 remedy against the yellowish tone of, 196 resume of the principal phenom- ena which may occur in, 196- 198 salts, prepared, 171 sheet iron, 209, 210 -steel, 209, 210 zinc, 199-209 small holes in, 198 solid, 189 sufficiently heavy, test for, 189 suspension of objects in, 190 tin-plate, 209 use of hand anode in, 190 wire, 210-212 gauze, 212, 213 with too strong a current, 187 yellowistutinge of, 197 Nickelous cyanide solution, addition of, to silver baths, 259 Niel, imitation of, 281, 282 Nielled, silvering, imitation of, 281, 282 Nielling powder, 281 , 282 Niello, Corvin's, 398, 399 Nitrates, 444-446 Nitre, 444 Nitric acid, 425 table of the specific gravity and content of, 471 Nitrous gases, poisoning by, 423, 424 Nobili, discovery of the production of iridescent colors by, 4 Nobili 's rings, 339-341 Noe's thermo-electric pile, 58 Non-electrics, 13 Norris and Johnson, brass bath ac- cording to, 242 North pole, 11 fABERNETTER, C., method of \/ steeling copper printing plates, employed by, 342, 343 Object wire, 103 coupling the, with the re- sistance boards, voltmeter, shunt and baths, 114 Object wires, insulation of, 111 INDEX. 491 Oersted, Prof., discoveries of, 3, 4 Ohm, law of, 4, 17, 18 the, 31 Ohm's law, proposition deduced from, 21 useful applications of, 18-21 Oil of vitriol, 424, 425 Old silvering, 282, 283 Oppermann's element, 44-48 Organic acids, salts of the, 446-448 Orpiment, 431 Over-nickeling, 187 Oxalate solution, preparation of, 321, 322 Oxidized silver, 283 Oxidizing, patinizing, coloring of metals, 403-417 T)ACINOTTI, invention by, of the ring named after him, 8 ring conductor of, 65 Painter's gold, 288 Palladium baths, 325 deposition of, 325, 326 properties of, 325 Pans, boiling, 164, 165 Paracelsus, silvering of copper and iron known to, 1 Paris Mint, method in the, for pro- ducing brown color on copper, 404, 405 Parkes's method of metallizing by the wet way, 394 Paste, cold silvering with, 277 Pastes, argentiferous, composition of, 277 Patina, bluish, 407 bronze-like on tin, 416 brown, on cast zinc, 414 definition of, 403 genuine, imitation of, 406, 407 green, 406 Patinizing, oxidizing, coloring of metals, 403-417 Pfanhauser, brass bath recommended by, 243 copper bath according to, 230, 231 tin bath according to, 328 Philadelphia Public Buildings, pro- cess employed for coating the col- umns of, with aluminium, 350 Philipp's process of coating laces and tissues with copper, 398 Phosphates and pyrophosphates, 446 Pickle, preliminary, 152 Pickles, recovery of gold from, 318 Pickling, 109, 150-156 duration of, 151 Pickling, manipulation of, 153, 154 production of a grained surface by, 156 Pile of Volta, 2 Piles, thermo-electric, 57-62 Pilet, palladium bath recommended by, 325, 326 Pins, nickeling of, 193 silvering of, 275 tinning solution for, 331 , 332 Pitchers, gilding the inner surfaces of, 297 Pixii, first attempt made by, to devise an electrical machine, 65 electro-magnetic machine constructed by, 4 Plaster of Paris, making of, imper- vious to fluids, 392, 393 moulding in, 391, 392 use of, for casts, 390-393 Plastic material, preparation of moulds in, 367-371 Plater's lathe goblet scratch brush, 123 Plates, printing, in relief, preparation of, 386, 387 Plating balance, 263-266 -room arranged by the Hanson & Van Winkle Co., 120 location of Bunsen elements in, 86 -rooms, best material for floors of, 87 light and air in, 85 provision for heating, 86 renewal of water in, 87 size of, 87, 88 sectional, 270 solutions, temperature of, 86 Platinic chloride, 434, 435 Platinizing by contact, 324 execution of, 323, 324 glass, 324 Platinum anodes, 293 insoluble, in silvering,253 baths, 319-322 management of, 322, 323 black, 318, 319 deposition of, 318-325 deposits, polishing of, 149 oxalate solution, preparation of, 321, 322 phosphate bath, preparation of, 322 properties of, 318 recovery of, from platinum solu- tions, 324, 325 Platoso-ammonium chloride, prepa- ration of, 319, 320 492 INDEX. Plunge batteries, 53-57 Poisoning by alkalies, 423 arsenic, 423 chlorine, sulphurous acid, nitrous and hyponitric gases, 423, 424 copper salts, 423 hydrocyanic (prussic) acid, potassium cyan- ide, or cyanides, 422.423 lead salts," 423 mercury salts, 423 sulphuretted hydrogen, 423 Polarization, 34 Polarizing current, 27, 192 phenomena, 191-193 Pole, north, 11 pieces, the, 64 south, 11 Poles, attraction and repulsion of, 11 magnetic, 10 Polishing, 137 bobs, 137 flexible shaft for, 143, 144 lathes, American double, 139 machines, location of, 88 self-acting, 202 materials, 144 rooms, 88 dust in, 88, 89 silvered articles, 267 wheels, compress, 137, 138 Poole, M., first use of thermo-elec- tricity by, 6 Porcelain gilding, 310 metallization of, 400 Positive wire, 103 Potash, 438 alum, 440, 441 caustic, 428 element, Dun's, 51, 52 yellow prussiate of, 437, 438 white prussiate of, 435, 436 Potassium and sodium, production of the amalgams of, 4 bitartrate, 446 carbonate, 438 solutions of, table of the specific gravity and con- tent of, 469 cyanide, 160, 435, 436 addition of, to silver baths, 253, 254 determination of proper pro- portion of, and silver in a silver bath, 256, 257 handling of, 422 Potassium cyanide, holders for baths containing, 105 poisoning by, 422, 423 proportion of, to fine silver in silver baths, 252 solutions, introduction of the use of, 5, 6 use of, as a pickle, 152 with a different con- tent, table of, 436 discovery of, 3 ferro cyanide, 437, 438 hydrate, 428 nitrate, 444 sodium tartrate, 447 stannate, preparation of, 332 sulphide, 430 Potential, electrical, 16 or electro-motive force, 30 Power, consumption of, in elec- trolysis, 0, 31 or force, 30 Pretsch, heliographic process in- vented by, 387 Primary current, 24 Prime & Son, perfection by, of the invention of depositing metals, 7 Printing plates in relief, preparation; of, 386, 387 Properties of silver, 249 Prussiate of silver, 437 zinc, 437 Prussic acid, 426 poisoning by, 422, 423 Pulley on counter-shaft carrying belt to machine, to find diame- ter of, 475 main shaft, to find diameter of, 475 Pyrophosphates and phosphates, 446 QUANTITY, 30 Quicking, 261 RAG, gilding with the, 310-312 Rain water, 159, 160 Ratsbane, 427 Rauber's sheet grinding and polish- ing machine, 1102-20 4 Reaumur, Centigrade and Fahrenheit thermometers, comparison of the scales of the, and rules for convert- ing one scale into another, 476 Recovery of silver from old silver baths, 285-287 Red brown color on copper, 405 zinc, 414 INDEX. 493 Red gilding, 298, 299 sulphide of antimony, 430 Reduction of metals without a bat- tery, 168, 169 Region of the lines of force, 63 Reinbold, H., formula for aluminium bath by, 349 Reliefs, cell apparatus for moulding, 355 Reproduction, 352-403 Resist, composition of, 279, 280 Resistance, 16, 17, 30 board, 93, 94 conditions upon which its action is based, 94. 95 Rheostat, 93, 94 improved, 96, 97 Rhodium, deposits of, 326 Rinsing apparatus, 108 Rivets, nickeling of, 193 Rochelle salt, 447 Rock salt, 431 Rogers Manufacturing Co., amount of silver upon plated ware, manufac- tured by the, 262, 263 methods in use b) r the, for prepar- ing work for platiug,269, 270 solution for silver plat- ing used by the, 270 striking solu- tion of the. 270 Rose-color gilding, 299 Roseleur, brass bath according to, I 239, 240 plating balance, improved by, 263-266 Rouge, 144 Roughing wheel, 132 Ruolz's bronze bath, 247 Russia gold, composition of, 287 SAL AMMONIAC, 431 solutions, table of the specific grav- ity of, 471 Salt, common, 431 rock, 431 Saltpetre, 444 Salts of the organic acids, 446-448 Salzede's bronze bath, 247 use of, for tinning cast iron, 328 Sandblast, 126-128 Satin finish, swing brushes for, 123 Sawdust, 148 Saw table, 382 Saxton, electric generator produced by, 65 Scamoni, heliographic process im- proved by, 387 Schuckert's flat ring dynamo, 69, 70 machine, 8 Scouring, brush for, 126 Scratch-brush, hand, mode of using the, 146, 147 -brushes, circular, 124, 125 treatment of, 124 various forms of, 123 -brushing, 123, 145-148 decoctions used in, 146 operation of, 124 Secondary current, 24 Sectional plating, 270 Seebeck, Prof., discovery of a new source of electricity by, 57 Seignette salt, 447 Sepia-brown tone upon tin and its alloys, 416 Shaft, flexible, 143, 144 Shaving machine, types of, 382, 383 Sheet grinding and polishing ma- chine, Rauber's, 202-204 iron, galvanized, 350 plated with aluminium, 350 Shell gold, 288 or deposit, backing the, 380-382 Shultz, O., patent of, for removing hydrochloric acid from the pores of coppered articles, 234 Shunt, the, 114 Siemens, Dr. W., discovery by, 65, 66 first machine of, 8 improvement in elec- tric generators made by, 65 & Halske dynamos, 8, 72-74 Silver, amount of, deposited upon plated ware, manufactured by the Wm. Rogers Co., 262, 263 anodes, 251-260 articles, stripping of, 316 bath, agitation of, 257, 258 determination of proper pro- portions of silver and potas- sium cyanide in a, 256, 257 494 INDEX. Silver bath, for ordinary electro silver- ing, 251 with silver chloride, prepara- tion of, 249, 2nO cyanide, preparation of, 250, 251 baths, 249-251 addition of certain substances to, 258 potassium cyanide to, 253, 254 solution of nickel- ous cyanide in potassium cyan- ide to, 259 augmentation of silver in, 254-256 current-strength for, 252 old, recovery of silver from, 285-287 prepared with chloride of sil- ver, life of, 254, 255 thickening of, 255 treatment of, 251-260 vats for, 251 chloride, 433, 434 preparation of silver bath, with, 249, 250 coloring, 417 control of the weight of the de- posit of, 263 cyanide, 437 preparation of, 251 deposition of, 249-287 deposits, polishing of, 149 extra heavy coating of, on the convex surfaces of spoons and forks, 270 fine, proportion of, to potassium cyanide in silver baths, 252 foot lathe for polishing, 138, 139 galvanoplastic operations in, 402, 403 -immersion bath, 274 incrustations with, 281 nitrate, 445, 446 of, solution of, in sodium sul- phide, 272 oxidized, 283 plate, foot lathe for polishing, 138, 139 recovery of, from old silver baths, 285-287 scratch-brushes for, 146 solder, table of, 468 solutions containing potassium cyanide, precipitation of silver from, 286, 287 Silvered articles, burnishing of, 267. 268 polishing of, 267 stripping of, 283, 284 yellow color on, 283 Silvering, amalgamating articles for, 261 antique, 282, 283 areas, 259, 260 bichromate element for, 55 by contact, by immersion, and cold silvering with paste, 271-277 weight, 260-268 cold, with paste, 277 coppering previous to, 268 current-density for, 92 electro-deposited, determination of, 284, 285 elements for, 252 execution of, 260-271 fine copper wire, 280 freeing from grease for, 261 in contact with zinc, bath for, 271 , 272 insoluble platinum anodes in, 253 Meriden Britannia Co.'s solution for, 270 methods in use by the Rogers Manufacturing Co. for prepar- ing work for, 269, 270 nielled, imitation of, 281, 282 old, 282, 283 ordinary, 268-271 bath for, 251 pickling for, 261 practice of the Meriden Britannia Co. in preparing articles for, 268, 269 preparation of Britannia hollow- ware for, 269. 270 metal for, 269, 270 nickel silver for, 269 Rogers Manufacturing Co.'s solu- tion for, 270 scratch-brushing, during, 262 singular phenomenon in, 258 yellow tone of, 258 Similor, 238 Sine galvanometer, 22 Siphons, 452, 453 Skates, removal of grease from, 157 Slinging wires, 108, 262 Smee, A., discoveries of, 6 experiments of, with copper, 353 INDEX. 495 Smee's element, 34, 35 Smoke-bronze, 411 Soda, caustic, 428 Sodium and potassium, production of the amalgams of, 4 bicarbonate, 439 bisulphite, 444 carbonate, 438, 439 chloride, 431 citrate, 448 discovery of, 3 hydrate, 428 nitrate, 444 phosphate, 446 pyrophosphate, 446 sulphate, 440 sulphide, preparation of solution of, 272-274 sulphite, 160,161, 443,444 Soft solder, table of, 468 Solder, gold, table of, 469 hard, table of, 468 silver, table of, 468 soft, table of, 468 Solders and most usual alloys, table showing the composition of, 466-469 table of. 468, 469 Soldering fluid, 380 Solenoid, the, 12 Solubility of various substances, table showing the, 466 South pole, 1 1 Spaeth, J. W., machine of, for gild- ing metallic wire and gauze, 303, 304 Speed, rules for, 475, 476 Spencer, T., claim of, to the inven- tion of the galvanoplastic process, 5 Spirit of hartshorn, 429 Spirit of nitre, 425 Spoons, deposit of silver on, 262 extra heavy coating of silver on the convex surfaces of, 270 German silver, preparation of, for silvering, 269 nickel silver, preparation of, for silvering, 269 slinging wires for, 262 Spring water, constituents of, 159 Stannic chloride, 432 Stannous chloride, 432 Stearine, moulding in, 370, 371 Steel articles, brightening of, 131 coating of, with lead, 339 co baiting, 223, 224 grinding of, 136 preparation of, for silver- ing, 269 Steel articles, tinning solution for, 331 Steel, bath for brassing, 242 baths, 341-344 blue on, 416 copper baths for, 226, 227 coppering of, previous to nickel- ing, 185, 186 current for nickeling, 188 direct gilding, bath for, 291, 292 gray color on copper, 407 on brass, 408, 409 objects, removal of oxide from, 158 thin film of copper on, 237 pens, coppering, 237 plates, use of, in place of silver anodes, 253 sheet, nickeling, 209, 210 spring carboy rocker, 158, 159 zinc bath for, 335 Steeling, 341-345 by contact, 345 execution of, 344 Stirring rods, 453 Stoehrer's battery, 56 Stolba, method of tinning according to, 333 Stolba's process for nickeling by con- tact, 217-219 Stopping off, 270, 271 varnish, 271 Storage batteries, electro-chemical process of forming, 378 Straw color, to brown through golden yellow, and tombac color on brass, 409 Striking solution, 268 Meriden Britannia Co. 's, 270 Rogers Manufacturing Co.'s, 270 Stripping acid, 195 gilded articles, 315, 316 nickeled articles, 194-196 silvered articles, 283, 284 Sugar of lead, 447, 448 Sulphates and sulphites, 440-444 Sulphites and sulphates, 440-444 Sulphur combinations, 429-431 Sulphuretted hydrogen, 429, 430 poisoning by, 423 Sulphuric acid, 424, 425 poisoning by, 423, 424 solutions, different, table of specific electrical re- sistances of, at various temperatures, 464 table of the specific grav- ity of, 470 496 INDEX. Sulphydrate of ammonia, 430 Sulphydric acid, 429, 430 Surgical instruments, coating wooden handles of, with cop- per, 400 sharp, nickeling, 213, 214 Swing brushes, 123 Switch-board, 93, 94 improved, 96, 97 T ABLE of actual diameters in dec imal parts of an inch corresponding to the numbers of various wire gauges, 473 approximate content of pure crystallized blue vitriol at different de- grees Be., and at 59 F., 358 chemical and electro- chemical equivalents, 402, 403 composition of the most usual alloys and sol- ders, 400-409 electrical resistance of pure copper \vire of various diameters, 472 electro-motive force of elements, 405 elements with their sym- bols, atomic weights and specific gravities, 401 high temperatures, 469 melting points of some metals, 409 potassium cyanide with a different content, 430 readings of different hy- drometers, 450 resistance and conductiv- ity of pure copper at different temperatures, 472 results of experiments with galvanoplastic baths at rest and in motion, 303 solubility of various sub- stances, 400 specific electrical resist- ances of different cop- per sulphate solutions at various tempera- tures, 404 Table of specific electrical resist- ances of different sul- phuric acid solutions at various tempera- tures, 404 specific gravity and con- tent of nitric acid, 471 specific gravity and con- tent of solutions of po- tassium carbonate, 409 specific gravity of sal ammoniac solutions, 471 specific gravity of sul- phuric acid, 470 value of equal current volumes as expressed in amperes per square decimetre, per square foot and per square inch of electrode sur- face, 463, 404 weights of iron, copper, and brass wire and plates, 474 Tables, useful, 401-470 Tacony Iron & Metal Co. of Philadel- phia, process used by the, for plat- ing the columns of the Philadelphia Public Buildings, 350 Tangent galvanometer, 22 Tanks, 103-105 Bossard Mechano- Electroplating, 455-401 Tartar emetic, 447 Taucher, C., gold bath recommended by, 292 tin bath according to,328,329 Temperatures, high, table of, 409 Terchloride of gold, 434 Terra-cotta, metallization of, 4CO Thermo-electric piles, 57-62 electricity, first use of, Thermometers, coating mercury ves- sels of, with copper, 400 Fahrenheit, Centigrade and Re% aumur, comparison of the scales of the, and rules for converting one scale into another, 470 Thompson, S. P., definition of a dy- namo-electric machine by, 04 Thumb, gilding with the, 310-312 Tin alloys, sepia brown tone upon, 410 baths, 327-329 current strength for, 329 management of, 329, 330 bronze- like patina on, 416 chloride, 432 INDEX. 497 Tin, coloring, 416 dark coloration on, 416 deposition of, 326-833 plate, nickeling, 209 properties of, 326 salt, 43^ sepia-brown tone upon, 416 Tinning by contact and boiling, 330, 331 process of, 330 Tissues, coating of, with copper, S98 Toggle press, 308, 369 Tombac, 238 deposits of, 248 pickling of, 151, 152 removal of oxide from, 158 Toys, metallic, metallo-chromy for ornamenting, 341 Tripoli, 144 Trough battery, 2, 32 Tumbling barrel, exhaust, 129, 130 dium, 128. 129 operation with the, 130-132 Twaddell's hydrometer, 450 T TMBREIT & Matthes element, 50 U United States, evolution of the dynamo in the, 77-84 Units, electric, 30 VARNISH, removal of, from an imperfectly varnished object, 420 Varnish, stopping off, 271 Varnishes and lacquers, cellulose, 417-419 for gold varnishers, 420 Varreutrapp, steel bath according to, 341 Vases, coloring gray, 346 galvanoplastic reproduction of, 388, 38;) Vats, 103-105 for copper baths, 231 gold baths, 294 nickeling sheet zinc, 207 silver baths, 251 Verdigris, 447 Vienna lime, 144 Violet on brass, 411 Vitriol, blue, 441 , 442 table of approximate con- tent of, at different de- grees Be., and at 59 F., 358 green, 441 oil of, 424, 425 white, 442 Volt, the, 3.1 32 Volta, A., 1 pole of, 2 Voltaic pile, 2 Voltmeter, 114 check, 454 Weston, 100, 101 WAHL, Dr. W. H., directions for preparing platinum baths by, 320-322 Walenn, copper bath, recommended by, 230 Wales gold, composition of, 287 Warren, cobalt solution described by, 223 nickel and cobalt solutions, de- scribed by, 194 Washing soda, 438, 439 Watch movements, plating of, with palladium, 325. 326 parts, grained, gilding of, 280 Watches, coloring hands and dials of, 341 Water, decomposition of, by elec- trolysis, 3 importance of, 159 renewal of, in plating rooms, 87 Watt, the, 31 Wax mixtures for moulding, 370, 371 mould, preparation of, 371 moulding in, 370, 371 Weil, copper bath of, 230 zincking according to, 337 and Newton's bronze bath, 247, 248 Weiler, L., conductivity of metals according to, 17 Well water, constituents of, 159 Weston ammeter, 102 boric acid as an addition to nick- eling baths recommended by, 171,172 dynamo, 77, 78 nickel bath recommended by, 175,176 voltmeter, 100, 101 Wheatstone, Sir C , discovery by, 65, 66 Wheel, fine, 132 medium, 132 roughing, 132 Wheels, compress polishing, 137, 138 White arsenic, 427 metal, preparation of, for silver- ing, 268, 269 prussiate of potash, 435, 436 vitriol, 442 Whiting, 439 498 INDEX. Wire, apparatus for nickeling, 211, 212 carriers, special, 111 gauze, nickeling, 212, 213 metallic, gilding of, 303-305 nickeling, 2h:-^12 Wires, conducting, 103 electrified, general law of the action of, 23 insulation of, 103 slinging, 108 Wollaston, discovery by, 3 "Wonder" dynamo, 7S, 79 Wood, coating of, with a gal van o- plastic deposit of copper, 31)9, 400 Wooden vats, construction of, 104 lined with sheet lead, 104, 105 Woolrych, original machine con- structed by, 7 Work, 30 Workshop, hygienic rules for the, 421-424 Wright, introduction by, of the use of potassium cyanide solutions, 5,6 Wrought iron, bath for brassing, 242 coating with bronze, 247 objects, pickling of, 150, 151 zinc bath for, 335 VBLLOW-BROWN shades on zinc, I 414 prussiate of potash, 437, 438 gold bath with, 290, 291 7APON, 417,418 j Zilken, solution for tinning by contact in a cold bath, patented by, 331 Zinc alloys, 337, 338 amalgamation of, 29, 33, 34 articles, copper bath for, 228 polished, slightly coppered, nickel bath for, 178 bath for brassing, 242 baths, 334-336 addition of salts of magne- sium and aluminium to, 335 for silvering in contact with, 271.272 black on, 413 blue black on, 413 bronzing on, 413. 414 carbonate, 439. 440 cast, brown patina on, 414 Zinc, cast, nickeling lamp-feet of, 190, 191 castings, nickel bath for, 178 polishing of, 136 chloride, 160, 432, 433 and ammonium chloride, 433 coating brass with, 337 copper with, 337 coloring. 413, 414 coppering of, 236 current for nickeling, 188 cyanide, 437 dead gilding on, 300, 01 deposition of, 333-338 gray coating on, 413 objects, brassed, bronze Barb- dienne on, 410 pickling of, 151 tinning of, 327 plates, to coat, with a very thin but hard layer of copper, 236 precipitation of gold by, 317 properties of, 333, 334 red brown color on, 414 reduction of chloride of silver by, 286 removal of oxide from, 158 scratch brushes for, 146 sheet, black streaks and stains on, in nickeling, 208 brassing of, 206 coppering of, 206, 207 current-density for nickel- ing, 207 freeing of, from grease, 204, 205 grinding or polishing of, 200, 201, 202 nickel bath for, 178 nickeled, polishing of, 208, 209 nickeling of, 199-209 phenomena in nickeling, 205, 206 polishing of, 136 prevention of the nickel de- posit peeling off, 206 vats for nickeling, 207 sulphate, 442 -tin alloy, production of, 337 -nickel alloy, production of, 337 yellow brown shades on, 414 Zincking, execution of, 336, 337 iron by contact, 337 Zone, neutral, 10 Zosimus, reduction of copper from its solution by iron described by, 1 The Hanson & Van Winkle Co., Newark, N. J., U. S. A. ELECTRO=PLATINQ OUTFITS FOR Gold, Silver, Nickel, Copper, Etc. Just a Word about Dynamos. Did you know that all the early experi- ments and improvements in Dynamos were made with a view of perfecting an electrical machine for plating, and that this success was the forerunner of all the magnificent Dynamo machines for other purposes in such general use to-day? In 1876 we began manufacturing the " Weston" Dynamo for electro-plating. This was the first machine in the mar- ket. It met with pronounced success, and to it can be traced the sudden development of electro-plating and electro- typing. Many of these machines are still in use. The Hanson & Van Winkle Co., Newark, N. J., U. S. A. In 1885 we brought out the "Little Wonder" Dynamo. It be- came very popular. Over one thousand were sold. In 1886 we be- gan manufacturing the "Wonder' Dynamo. It em- bodied many new improvements, and we thought then that we had reached perfection. In 1891 electrical science had devel- oped so many en- tirely new features, that in order to maintain our emi- nent position as leaders in the pro- duction of plating machines, we brought out our H. & V. W. Dynamo. It embodied every late idea, and has had a remarkable sale. (On the following page we show our new IRON CLAD Dynamo. This also marks a new era in plating dynamos.) 2 The Hanson & Van Winkle Co., Newark, N. J., U. S. A. If You are Interested in Electro-plating, Electro typing, Electro-refining of Metals or other. Electro-chemical operations, you will naturally feel in- terested in anything that tends to bring these industries to the highest stage of development. In Introducing this new dynamo to your notice, we feel that we are urging the claims of a machine which will materially aid you in reaching that point. Many who have only used the old style machines have no idea of the improvements that have recently been made in this class of dy- namos; improvements that save time, money, labor and trouble. There are Several dynamos which are marked improvements on the old style of machines, but the new IRON CLAD, while embracing all the good points found in other modern machines, has several im- provements distinctively its own, and is the result of years of experimenting; there are no unusual number of brushes as in some other Dynamos, in some requiring 24 to 36 brushes to wear the Commutator and the patience of the plater. 3 The Hanson & Van "Winkle Co., Newark, N. J., U. S. A. CAST ANODES OF ALL METALS ANY SIZE. Nickel: We are first hands in nickel and other metals, and the largest manufacturers of the various Metallic Salts, of Nickel, Silver, Copper and Gold, and of Cyanide of Potassium. Plating Solutions: We furnish Concentrated Plat- ing] Solutions of Silver, Gold, Copper, Nickel, Brass, etc. Batteries of all kinds. Our No. 1 H. & V. W. Battery has had a larger sale than any other for Electro- Plating and experimental work. Anodes : Our Cast Nickel Anodes are standard for whitest results. Anodes of Nickel, Silver, Gold, Electro-deposited Cop- per, Brass, etc. Nickel cast- ings. Tanks: i Porcelain-lined, Iron, Wood, Slate, etc. , for all purposes. Lacquers : Patent Celluloid Lacquers for metal, paper, etc. Gold and colored Lacquers. Chemical Solution : For removing sand, scale, etc. , from castings, etc. The Hanson & Van Winkle Co., Newark, N. J., U. S. A. No. 4 Polishing and Buffing Lathe. SPINDLE 50 INCHES LONG, If INCH DIAMETER IN BOXES. This machine is designed for heavy work. It is fitted with extra long boxes, giving the spindle sufficient bearing to insure stiffness. Without sacrificing strength, we have so reduced the width of head that the ma- chine will be found especially desirable by manufacturers of large, irreg- ular pieces, and will commend itself to any one having bicycle, stove, chandelier or car trimmings to do, as with this lathe there is no inter- ference when working on large pieces. With this machine you can use a large wheel without the slightest jar or spring. We show above a sample of one of our most salable Polishing Lathes. 5 The Hanson & Van Winkle Co., Newark, N. J., U. S. A. We manufacture a complete line of; GRINDING,- ; Polishing and Buffing Machines, and all the Various Wheels and Buffs and Grinding and Polishing Material. FELT VIENNA LIME COMPRESS CARBORUNDUM EMERY WOOD CROCUS SHEEPSKIN WALRUS ROUGE PAPER PUMICE 6 The Hanson & Van "Winkle Co., Newark, N. J., U. S. A. POLISHING SUPPLIES. TRIPOLI COMPOSITION. Tripoli Composition is especially adapted for cutting down and polishing Brass, Bronze, Brittannia, and other metals preparatory to plating. Standard Tripoli Composition, O. S. for cutting and polishing, . per Ib. " " " M, very greasy .... " " " " No. 6, hard and fast cutting . . " " " " H, very fast cutting ... " No. 9, similar to O. S. , slightly sharper, ' ' CROCUS COMPOSITION. Crocus Composition is largely used by stove manufacturers and others desiring to produce smooth finished surface on cast iron and steel. A, greasy, fast cutting . . . . ..... . per Ib. F. F., dry and fast cutting . . . . . . . S, dry and fast cutting . . . . . . . . O. S., very finest grade of this material . . . . " Emery Cake *~ "\ . " Emery Paste . V , . . . ., .. \ " English Crocus, powdered, in kegs and casks . . - . . . " 7 The Hanson & Van Winkle Co., Newark, N. J., U. S. A. POLISHING SETT. No. 200 Complete Box of Polishing Tools and Powders for small work . . $3.00 When ordered with No. 22 or 24 Lathe, $2.00, with samples of Lacquer. 8 The Hanson & Van Winkle Co., Newark, N. J., U. S. A. XXX BUFFING COMPOUND. For polishing and coloring all metals where the higher color is required, with the greatest economy of time, and especially for work that is engraved or ornamented where rouge is objectionable. Put up in cakes similar to Tripoli : '*,.. . . per Ib. VIENNA LlflE. We are the largest importers of this article, and furnish it both in lump and powder, and send full instructions for getting best results. There is an increasing demand for this article for nickel and other work, and we are paying special attention to the quality. Our 1(>0 page Catalogue mailed on application to any ad- dress in the w>rld. THE HANSON 8 VfiN WINKLE CO., MANUFACTORY AND OFFICES: 219 & 221 flarket Street, Newark, N. J., U. S. A. NEW YORK OFFICE : WESTERN BRANCH : 136 Liberty Street. 35 & 37 S. Canal St., Chicago, 111. 13 St. Paul Square, Birmingham, England. 9 OF practical and Scientific PUBLISHED BY HENRY CAREY BAIRD & Co, INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS. 810 Walnut Street, Philadelphia. & Any of the Books comprised in this Catalogue will he sent hy mail, free erf postage, to any address in the world, at the publication prices, 43- A Descriptive Catalogue, 90 pages, 8vo., will be sent free and free of postage, to any one in any part of the world, who will furnish his address, 4ST- Where not otherwise stated, all of the Books in this Catalogue are bound in muslin, AMATEUR MECHANICS' WORKSHOP: A treatise containing plain and concise directions for the manipula- tion of Wood and Metals, including Casting, Forging, Brazing, Soldering and Carpentry. By the author of the " Lathe and Its Uses." Seventh edition. Illustrated. 8vo. . . . $2.50 ANDRES. A Practical Treatise on th Fabrication of Volatile and Fat Varnishes, Lacquers, Yiccatives and Sealing Waxes. From the German of ERWIN ANDRES, Manufacturer of Varnishes and Lacquers. With additions on the Manufacture and Application of Varnishes, Stains for Wood, Horn, Ivory, Bone and Leather. From the German of DR. EMIL WINCKLER and Louis E. ANDES. The whole translated and edited by WILLIAM T. BRANNT. With n illustrations. I2mo. ....... ARLOT. A Complete Guide for Coach Painters : Translated from the French of M. ARLOT, Coach Painter, for eleven years Foreman of Painting to M. Eherler, Coach Maker, Paris. By A. A. FESQUET, Chemist and Engineer. To which is added an Appendix, containing Information respecting the Materials and the Practice of Coach and Car Painting and Varnishing in the United States and Great Britain T2mo. . . . 1.25 (0 HENRY CAREY BAIRD & CO.'S CATALOGUE. ARMENGAUD, AMOROUX, AND JOHNSON. The Practi- cal Draughtsman's Book of Industrial Design, and Ma^ chinist's and Engineer's Drawing Companion : Forming a Complete Course of Mechanical Engineering and Archi tectural Drawing. From the French of M Armengaud the elder, Prof, of Design in the Conservatoire of Arts and Industry, Paris, and MM. Armengaud the younger, and Amoroux, Civil Engineers. Re- written and arranged with additional matter and plates, selections from and examples of the most useful and generally employed mechanism of the day. By WILLIAM JOHNSON, Assoc. Inst. C. E. Illustrated by fifty folio steel plates, and fifty wood-cuts. A new edition, 4to , cloth $6.00 ARMSTRONG. The Construction and Management of Steam Boilers : By R. ARMSTRONG, C. E. With an Appendix by ROBERT MALLET, C. E., F. R. S. Seventh Edition. Illustrated. I vol. I2mo. 75 ARROWSMITH. Paper-Hanger's Companion : A Treatise in which the Practical Operations of the Trade are Systematically laid down : with Copious Directions Preparatory to Papering; Preventives against the Effect of Damp on Walls; the various Cements and Pastes Adapted to the Several Purposes ol the Trade ; Observations and Directions for the Panelling and Ornamenting of Rooms, etc. By JAMES ARROWSMITH. I2mo., cloth .......... $1.00 A.SHTON. The Theory and Practice of the Art of Designing Fancy Cotton and Woollen Cloths from Sample : Giving full instructions for reducing drafts, as well as the methods of spooling and making out harness for cross drafts and finding any re- quired reed; with calculations and tables of yarn. By FREDERIC T. ASHTON, Designer, West Pittsfield, Mass. With fifty-two illustrations. One vol. folio #5- ASKINSON. Perfumes and their Preparation : A Comprehensive Treatise on Perfumery, containing Complete Directions for Making Handkerchief Perfumes, Smelling-Salts, Sachets, Fumigating Pastils ; Preparations for the Care of the Skin, the Mouth, the Hair; Cosmetics, Hair Dyes, and other Toilet Articles. By G. W. ASKINSON. Translated from the German by IsiDOR FURST. Revised by CHARLES RICE. 32 Illustrations. 8vo. $3.00 3AIRD. Miscellaneous Papers on Economic Questions. By Henry Carey Baird. {In preparation.} BAIRD. The American Cotton Spinner, anc Manager's and Carder's Guide: A Practical Treatise on Cotton Spinning ; giving the Dimensions and Speed of Machinery, Draught and Twist Calculations, etc. ; with notices of recent Improvements : together with Rules and Examples rbr making changes in the sizes and numbers of Roving and Yarn. Compiled from the papers of the late ROBERT H. BAIRD. i2mo. HENRY CAREY BAIRD & CO.'S CATALOGUE. BAIRD. Standard Wages Computing Tables : An Improvement in all former Methods of Computation, so arranged that wages for days, hours, or fractions of hours, at a specified rate per day or hour, may be ascertained at a glance. By T. SPANGLER BAIRD. Oblong folio ....... $5.00 3AKER. Long-Span Railway Bridges: Comprising Investigations of the Comparative Theoretical and Practical Advantages of the various Adopted or Proposed Type Systems of Construction; with numerous Formulae and Tables. By B. BAKER. i2mo. $1.00 BAKER. The Mathematical Theory of the Steam-Engine : With Rules at length, and Examples worked out for the use of Practical Men. By T. BAKER, C. E., with numerous Diagrams. Sixth Edition, Revised by Prof. J. R. YOUNG. I2mo. . 75 BARLOW. The History and Principles of Weaving, by Hand and by Power: Reprinted, with Considerable Additions, from " Engineering," with a chapter on Lace-making Machinery, reprinted from the Journal of the "Society of Arts." By ALFRED BARLOW. With several hundred illustrations. 8vo., 443 pages ..... $10.00 BARR. A Practical Treatise on the Combustion of Coal: Including descriptions of various mechanical devices for the Eco- nomic Generation of Heat by the Combustion of Fuel, whether solid, liquid or gaseous. 8vo. ....... $2.50 BARR. A Practical Treatise on High Pressure Steam Boilers: Including Results of Recent Experimental Tests of Boiler Materials, together with a Description of Approved Safety Apparatus, Steam Pumps, Injectors and Economizers in actual use. By WM. M. BARR. 204 Illustrations. 8vo. . ....". $3.00 BAUERMAN. A Treatise on the Metallurgy of Iron : Containing Outlines of the History of Iron Manufacture, Methods of Assay, and Analysis of Iron Ores, Processes of Manufacture of Iron and Steel, etc., etc. By H. BAUERMAN, F. G. S., Associate of the Royal School of Mines. Fifth Edition, Revised and Enlarged. Illustrated with numerous Wood Engravings from Drawings by J. B. JORDAN. i2mo. ........ $2.oc BRAN NT. The Metallic Alloys : A Practical Guide For the Manufacture of all kinds of Alloys, Amalgams, and Solders, used by Metal- Workers; together with their Chemical and Physical Properties and their Application in the Arts and the Industries; with an Appendix on the Coloring of Alloys and the Recovery of Waste Metals. By WILLIAM T. BRANNT. 34 Engravings. A New, Re- vised, and Enlarged Edition. 554 pages. 8vo. . . $4.50 BEANS. A Treatise on Railway Curves and Location of Railroads : By E. \V. BEANS, C. E. Illustrated. I2mo. Tucks . $1.50 BECKETT. A Rudimentary Treatise on Clocks, and Watches and Bells : By Sir EDMUND BECKETT, Bart., LL. D., Q. C. F. R. A. S. With numerous illustrations. Seventh Edition, Revised and Enlarged. I2mo. ... $22* HENRV CAREY BAIRD & CO.'S CATALOGUE. BELL. Carpentry Made Easy: Or, The Science and Art of Framing on a New and Improved System. With Specific Instructions for Building Balloon Frames, Barn Frames, Mill Frames, Warehouses, Church Spires, etc. Comprising also a System of Bridge Building, with Bills, Estimates of Cost, and valuable Tables. Illustrated by forty-four plates, comprising Dearly 200 figures. By WILLIAM E. BELL, Architect and Practical Builder. 8vo. .......... $5.00 BEMROSE. Fret-Cutting and Perforated Carving: With fifty-three practical illustrations. By W. BEMROSE, JR. i vol. quarto .......... $2.50 BEMROSE. Manual of Buhl-work and Marquetry: With Practical Instructions for Learners, and ninety colored designs. By W. BEMROSE, JR. I vol. quarto .... $3.00 BEMROSE. Manual of Wood Carving: With Practical Illustrations for Learners of the Art, ~.nd Original and Selected Designs. By WILLIAM BEMROSE, JR. With an Intro- duction by LLEWELLYN JEWITT, F. S. A., etc. With 128 illustra- tions, 410. -. #2.50 BILLINGS. Tobacco : Its History, Variety, Culture, Manufacture, Commerce, and Various Modes of Use. By E. R. BILLINGS. Illustrated by nearly 200 engravings. 8vo. . . . . . . . #3.00 BIRD. The American Practical Dyers' Companion : Comprising a Description of the Principal Dye-Stuffs and Chemicals used in Dyeing, their Natures and Uses; Mordants, and How Made; with the best American, English, French and German processes for Bleaching and Dyeing Silk, Wool, Cotton, Linen, Flannel, Felt, Dress Goods, Mixed and Hosiery Yarns, Feathers, Grass, Felt, Fur, Wool, and Straw Hats, Jute Yarn, Vegetable Ivory, Mats, Skins, Furs, Leather, etc., etc. By Wood, Aniline, and other Processes, together with Remarks on Finishing Agents, and Instructions in the Finishing of Fabrics, Substitutes for Indigo, Water-Proofing of Materials, Tests and Purification of Water, Manufacture of Aniline and other New Dye Wares, Harmonizing Colors, etc., etc. ; embrac- ing in all over 800 Receipts for Colors and Shades, accompanied by 170 Dyed Samples of Raw Materials and Fabrics. By F. J. BIRD, Practical Dyer, Author of " The Dyers' Hand-Book." 8vo. $10.00 BLINN. A Practical Workshop Companion for Tin, Sheet- Iron, and Copper-plate Workers : Containing Rules for describing various kinds of Patterns used by Tin, Sheet-Iron and Copperplate Workers; Practical Geometry; Mensuration of Surfaces and Solids ; Tables of the Weights of Metals, Lead-pipe, etc.; Tables of Areas and Circumference* of Circles; Japan, Varnishes, Lackers, Cements, Compositions, etc., etc. By LEROY J. BLINN, Master Mechanic. With One Hundred and Seventy Illustrations. I2tno. . . . . . $2.50 HENRY CAREY BAIRD & CO.'S CATALOGUE. BOOTH. Marble Worker's Manual: Containing Practical Information respecting Marbles in general, theii Cutting, Working and Polishing ; Veneering of Marble ; Mosaics ; Composition and Use of Artificial Marble, Stuccos, Cements, Receipts, Secrets, etc., etc. Translated from the French by M. L. BOOTH. With an Appendix concerning American Marbles. I2mo., cloth $1.50 BOOTH and MORFIT. The Encyclopaedia of Chemistry, Practical and Theoretical : Embracing its application to the Arts, Metallurgy, Mineralogy, Geology, Medicine and Pharmacy. By JAMES C. BOOTH, Melter and Refiner in the United States Mint, Professor of Applied Chem- istry in the Franklin Institute, etc., assisted by CAMPBELL MORFIT, author of " Chemical Manipulations," etc. Seventh Edition. Com- plete in one volume, royal 8vo., 978 pages, with numerous wood-cuts and other illustrations . . . . . . $3-5 BRAM WELL. The Wool Carder's Vade-Mecum, A Complete Manual of the Art of Carding Textile Fabrics. By W. C. BRAMWELL. Third Edition, revised and enlarged. Illustrated. Pp. 400. I2mo $2.50 BRANNT. A Practical Treatise on Animal and Vegetable Fats and Oils : Comprising both Fixed and Volatile Oils, their Physical and Chem- ical Properties and Uses, the Manner of Extracting and Refining them, and Practical Rules for Testing them ; as well as the Manufac- ture of Artificial Butter and Lubricants, etc., with lists of American Patents relating to the Extraction, Rendering, Refining, Decomposing, and Bleaching of Fats and Oils. By WILLIAM T. BRANNT, Editor of the " Techno-Chemical Receipt Book." Second Edition, Revised and in a great pi>rt Rewritten. Illustrated by 302 Engravings. In Two Volumes. 1304 pp. 8vo. ..... $10.00 BRANNT. A Practical Treatise on the Manufacture of Soap and Candles : Based upon the most Recent Experiences in the Practice and Science ; comprising the Chemistry, Raw Materials, Machine-v. and Utensils and Various Processes of Manufacture, including a great variety of formulas. Edited chiefly from the German of Dr. C. Deite, A. Engelhardt, Dr. C. Schaedler and others ; with additions and list? of American Patents relating to these subjects. By WM. T. BRANNT. Illustrated by 163 engravings. 677 pages. 8vo. . . #7.50 BRANNT. A Practical Treatise on the Raw Materials and the Distillation and Rectification of Alcohol, and the Prepara- tion of Alcoholic Liquors, Liqueurs, Cordials, Bitters, etc.: Edited chiefly from the German of Dr. K. Stammer, I)r. F. Eisner, and E. Schubert. By WM. T. BRANNT. Illustrated by thirty-one engravings. I2mo. ....... $3-5 HENRY CAREY BAIRD & CO.'S CATALOGUE. BRANNT WAHL. The Techno-Chemical Receipt Book: Containing several thousand Receipts covering the latest, most ;ra portant, and most useful discoveries in Chemical Technology, and their Practical Application in the Arts and the Industries. Edited chiefly from the German of Drs. Winckler, Eisner, Heintze, Mier- zinski, Jacobsen, Koller, and Heinzerling, with additions by WM. 1 BRANNT and WM. H. WAHL, PH. D. Illustrated by 78 engravings. I2mo. 495 pages ... ... . 552 oO 1 ROWN. Five Hundred and Seven Mechanical Movements: Embracing all those which are most important in Dynamics, Hy- draulics, Hydrostatics, Pneumatics, Steam-Engines, Mill and other Gearing, Presses, Horology and Miscellaneous Machinery; and in- cluding many movements never before published, and several of which have only recently come into use. By HENRY T. BROWN I2mo ........... $i.oc BUCKM ASTER. The Elements of Mechanical Physics : By J. C. BUCKMASTER. Illustrated with numerous engravings. I2mo ........... $1.00 BULLOCK. The American Cottage Builder : A Series of Designs, Plans and Specifications, from $200 to $20,000, for Homes for the People ; together with Warming, Ventilation, Drainage, Painting and Landscape Gardening. By JOHN BULLOCK, Architect and Editor of " The Rudiments of Architecture and Building." etc., elc. Illustrated by 75 engravings. 8vo. $ 2 -5 BULLOCK. The Rudiments of Architecture and Building: For the use of Architects, Builders, Draughtsmen, Machinists, En- gineers and Mechanics. Edited by JOHN BULLOCK, author of "The American Cottage Builder." Illustrated by 250 Engravings. 8vo. $2.50 BURGH. Practical Rules for the Proportions of Modern Engines and Boilers for Land and Marine Purposes. By N. P. BURGH, Engineer. I2mo. .... $1.50 BYLES. Sophisms of Free Trade and Popular Political Economy Examined. 13y a BARRISTER (SIR JOHN BARNARD BYLES, Judge of Common Pleas). From the Ninth English Edition, as published by ihc Manchester Reciprocity Association. I2mo. . . . $1.25 BOWMAN. The Structure of the Wool Fibre in its Relation to the Use of Wool for Technical Purposes : Being the substance, with additions, of Five Lectures, deliverea JOHN H. COOPER, M. E. 8vo CRAIK. The Practical American Millwright and M^ler. By DAVID CRAIK, Millwright. Illustrated by numerous wood en gravings and two folding plates. 8vo $3.50 HENRY CAREY BAIRD & CO.'S CATALOGUE. 9 CROSS. The Cotton Yarn Spinner : Showing how the Preparation should be arranged for Different Counts of Yarns by a System more uniform than has hitherto been practiced ; by having a Standard Schedule from which we make all' our Changes. By RICHARD CROSS. 122 pp. I2mo. . 75 CRISTIANI. A Technical Treatise on Soap and Candles: With a Glance at the Industry of Fats and Oils. By R. S. CRIS- TIANI, Chemist. Author of " Perfumery and Kindred Arts." Illus- trated by 176 engravings. 581 pages, 8vo. . . . $15.00 COAL AND METAL MINERS' POCKET BOOK: Of Principles, Rules, Formulae, and Tables, Specially Compiled and Prepared for the Convenient Use of Mine Officials, Mining En- gineers, and Students preparing themselves for Certificates of Compe- tency as Mine Inspectors or Mine Foremen. Revised and Enlarged edition. Illustrated, 565 pages, small I2mo., cloth. ', $2.00 Pocket book form, flexible leather with flap . . #2.75 DAVIDSON. A Practical Manual of House Painting, Grain- ing, Marbling, and Sign- Writing: Containing full information on the processes of House Painting in Oil and Distemper, the Formation of Letters and Practice of Sign- Writing, the Principles of Decorative Art, a Course of Elementary Drawing for House Painters, Writers, etc., and a Collection of Useful Receipts. W 7 ith nine colored illustrations of Woods and Marbles, and numerous wood engravings. By ELLIS A. DAVIDSON. I2tno. #3 DAVIES. A Treatise on Earthy and Other Minerals and Mining: By D. C. DAVIES, F. G. S., Mining Engineer, etc. Illustrated by 76 Engravings. I2mo. . $S DAVIES. A Treatise on Metalliferous Minerals and Mining: By D. C. DAVIES, F. G. S., Mining Engineer, Examiner of Mines, Quarries and Collieries. Illustrated by 148 engravings of Geological Formations, Mining Operations and Machinery, drawn from the practice of all parts of the world. Fifth Edition, thoroughly Revised and much Enlarged by his son, E. Henry Davies. I2mo., 524 pages . . . . . . . . $$-oo DAVIES. A Treatise on Slate and Slate Quarrying: Scientific, Practical and Commercial. By D. C. DAVIES, F. G. S., Mining Engineer, etc. With numerous illustrations and folding plates. I2mo. . . $2.00 DAVIS. A Practical Treatise on the Manufacture of Brick, Tiles and Terra-Cotta : Including Stiff Clay, Dry Clay, Hand Made, Pressed or Front, and Roadway Paving Brick, Enamelled Brick, with Glazes and Colors, Fire Brick and Blocks, Silica Brick, Carbon Brick, Glass Pots, Re- 10 HENRY CAREY BAIRD & CO.'S CATALOGUE. torts, Architectural Terra-Cotta, Sewer Pipe, Drain Tile, Glazed and Unglazed Roofing Tile, Art Tile, Mosaics, and Imitation of Intnrsia ^ or Inlaid Surfaces. Comprising every product of Clay employed in Architecture, Engineering, and the Blast Furnace. With a Detailed Description of the Different Clays employed, the Most Modern Machinery, Tools, and Kilns used, and the Processes for Handling, Disintegrating, Tempering, and Moulding the Clay into Shape, Dry- ing, Setting, and Burning. By Charles Thomas Davis. Third Edi- tion, Revised and in great part rewritten. Illustrated by 261 engravings. 662 pages . . . . . . . $5 oo DAVIS. A Treatise on Steam-Boiler Incrustation and Meth- ods for Preventing Corrosion and the Formation of Scale: By CHARLES T. DAVIS. Illustrated by 65 engravings. 8vo. $2.00 DAVIS. The Manufacture of Paper: Being a Description of the various Processes for the Fabrication, Coloring and Finishing of every kind of Paper, Including the Dif- ferent Raw Materials and the Methods for Determining their Values, the Tools, Machines and Practical Details connected with an intelli- gent and a profitable prosecution of the art, -with special reference to the best American Practice. To which are added a History of Pa- per, complete Lists of Paper-Making Materials, List of American Machines, Tools and Processes used in treating the Raw Materials, and in Making, Coloring and Finishing Paper. By CHARLES T. DAVIS. Illustrated by 156 engravings. 608 pages, 8vo. $6.00 DAVIS. The Manufacture of Leather: Being a Description of all the Processes for the Tanning and Tawing with Bark, Extracts, Chrome and all Modern Tannages in General Use, and the Currying, Finishing and Dyeing of Every Kind of Leather; Including the Various Raw Materials, the Tools, Machines, and all Details of Importance Connected with an Intelligent and Profitable Prosecution of the Art, with Special Reference to the Best American Practice. To which are added Lists of American Patents ( 1884-1897) for Materials, Processes, Tools and Machines for Tanning, Currying, etc. By CHARLES THOMAS DAVIS. Second Edition, Revised.' and in great part Rewritten. Illustrated by 147 engravings and 14 Sam- ples of Quebracho Tanned and Aniline Dyed Leathers, 8vo, cloth, 712 pages. Price ........ $7-5 DAWIDOWSKY BRANNT. A Practical Treatise on the Raw Materials and Fabrication of Glue, Gelatine, Gelatine Veneers and Foils, Isinglass, Cements, Pastes, Mucilages, etc. : Based upon Actual Experience. By F. DAWIDOWSKY, Technical Chemist. Translated from the German, with extensive additions, including a description of the most Recent American Processes, by WILLIAM T. BRANNT, Graduate of the Royal Agricultural College of Eldena, Prussia. 35 Engravings. I2mo. . . . $2.50 DE GRAFF. The Geometrical Stair-Builders' Guide : being a Plain Practical System of Hand-Railing, embracing all iti necessary Details, and Geometrically Illustrated by twenty-two Steel Engravings; together with the use of the most approved principle? of Practical Geometry. By SIMON DE GRAFF, Architect 410. $2.CO HENRY CAREY BAIRD & CO.'S CATALOGUE. n DE KONINCK DIETZ. A Practical Manual of Chemical Analysis and Assaying : A.S applied to the Manufacture of Iron from its Ores, and to Cast Iron, Wrought Iron, and Steel, as found in Commerce. By L. L. DH KoNiNCK, Dr. Sc., and E. DIETZ, Engineer. Edited with Notes, by ROBERT MALLET, F. R. S., F. S. G., M. I. C. E., etc. American Edition, Edited with Notes and an Appendix on Iron Ores, by A. A. FESQUET, Chemist and Engineer. I2mo. . ; $ l ~$Q DJNCAN. Practical Surveyor's Guide: Containing the necessary information to make any person of com* n'.on capacity, a finished land surveyor without the aid of a teacher Bv ANDREW DUNCAN. Revised. 72 engravings, 214 pp. I2mo. $1.50. DUPLAIS. A Treatise on the Manufacture and Distillation of Alcoholic Liquors : Comprising Accurate and Complete Details in Regard to Alcohol from Wine, Molasses, Beets, Grnin, Rice, Potatoes, Sorghum, Aspho- del, Fitiits, etc. ; with the Distillation and Rectification of Brandy Whiskey, Rum, Gin, Swiss Absinthe, etc., the Preparation of Aro- matic Waters, Volatile Oils or Essences, Sugars, Syrups, Aromatic Tinctures, Liqueurs, Cordial Wines, Effervescing Wines, etc., the Ageing of Brandy .and the improvement of Spirits, with Copious Directions and Tables for Testing and Reducing Spirituous Liquors, etc., etc. Translated and Edited from the French of MM. DUPLAIS, Aine ft Jeune. By M. McKENNiE, M. D. To which are added the United States Internal Revenue Regulations for the Assessment and Collection of Taxes en Distilled Spirits. Illustrated by fourteen folding plates and several wood engravings. 743 pp. 8vo. $12.50 DUSSAUCE. Practical Treatise on the Fabrication of Matches, Gun Cotton, and Fulminating Powder. By Professor H DUSSAUCE. I2mo. .... DYER AND COLOR-MAKER'S COMPANION: Containing upwards of two hundred Receipts for making Colors, on the most approved princip'es, for all the various styles and fabrics now in existence; with the Scouring Process, and plain Directions for Preparing, Washing-off, and Finishing the Goods. I2mo. $1.00 EDWARDS. A Catechism of the Marine Steam-Engine, . For the use of Engineers. Firemen, and Mechanics. A Practical Work for Practical Men. By EMORY EDWARDS, Mechanical Engi- neer. Illustrated by sixty-three Engravings, including examples <>f the most modern Engines. Third edition, thoroughly revised, with much additional matter. 12 mo. 414 pages . . . $2 or. EDWARDS. Modern American Locomotive Engines, Their Design, Construction and Management. By EMORY EDWARDS. Illustrated I2mo $2.00 EDWARDS. The American Steam Engineer: Theoretical and Practical, with examples of the latest and most ap- proved American practice in the design and construction of Steam Engines and Boilers. For the use of engineers, machinists, boiler- ipikers, and engineering students. By EMORY EDWARDS. Fully illustrated, 419 pages. I2mo. . . . $2.50 12 HENRY CAREY BAIRD & CO.'S CATALOGUE. EDWARDS. Modern American Marine Engines, Boilers, an* Screw Propellers, Their Design and Construction. Showing the Present Practice ot the most Eminent Engineers and Marine Engine Builders in the United States. Illustrated by 30 large and elaborate plates. 410. $$.oc EDWARDS. The Practical Steam Engineer's Guide In the Design, Construction, and Management of American Stationary. Portable, and Steam Fire- Engines, Steam Pumps, Boilers, Injectors, Governors, Indicators, Pistons and Rings, Safety Valves and Steam Gauges. For the use of Engineers, Firemen, and Steam Users. B> EMORY EDWARDS. Illustrated by 119 engravings. 420 pages. I2mo. $2 50 EISSLER. The Metallurgy of Gold : A Practical Treatise on the Metallurgical Treatment of Gold-Bear- ing Ores, including the Processes of Concentration and Chlorination, and the Assaying, Melting, and Refining of Gold. By M. EISSLER. With 132 Illustrations. I2mo. ..... $5.00 EISSLER. The Metallurgy of Silver : A Practical Treatise on the Amalgamation, Roasting, and Lixiviation of Silver Ores, including the Assaying, Melting, and Refining of Silver Bullion. By M. EISSLER. 124 Illustrations. 336 pp. I2mo $425 ELDER. Conversations on the Principal Subjects of Political Economy. By DR. WILLIAM ELDER. 8vo $2 50 ELDER. Questions of the Day, Economic and Social. By DR. WILLIAM ELDER. 8vo. . $3.00 ERNL Mineralogy Simplified. Easy Methods of Determining and Classifying Minerals, including Ores, by means of the Blowpipe, and by Humid Chemical Analysis, based on Professor von Kobell's Tables for the Determination of Minerals, with an Introduction to Modern Chemistry. By HENRY ERNI, A.M., M.D., Professor of Chemistry. Second Edition, rewritten, enlarged and improved. I2mo. ..... FAIRBAIRN. The Principles of Mechanism and Machinery of Transmission Comprising the Principles of Mechanism, Wheels, and Pullevs, Strength and Proportions of Shafts, Coupling of Shafts, and Engag- ing and Disengaging Gear. By SIR WILLIAM FAIRBAIRN, Bait C. E. Beautifully illustrated by over 150 wood-cuts. In one volume. I2mo . . . $2.00 FLEMING. Narrow Gauge Railways in America. A Sketch of their Rise, Progress, and Success. Valuable Statistics as to Grades, Curves, Weight of Rail, Locomotives, Cars, etc. By HOWARD FLEMING. Illustrated, 8vo $i oa FORSYTH. Book of Designs for Headstones, Mural, and oth&f Monuments : Containing 78 Designs. By JAMES FORSYTH. With an Introduction by CHARLES BCUTELL, M. A. 4 to., cloth . . HENRY CAREY BAIRD & CO.'S CATALOGUE. '3 FRANKEL HUTTER. A Practical Treatise on the Manu* facture of Starch, Glucose, Starch-Sugar, and Dextrine: Based on the German of LADISLAUS VON WAGNER, Professor in the Royal Technical High School, Buda-Pest, Hungary, and other authorities. By JULIUS FRANKEL, Graduate of the Polytechnic School of Hanover. Edited by ROBERT HUTTER, Chemist, Practical Manufacturer of Starch-Sugar. Illustrated by 58 engravings, cover- ing every branch of the subject, including examples of the most Recent and Best American Machinery. 8vo., 344 pp. . $3 50 TARDNER. The Paintev's Encyclopaedia: Containing Definitions of a.l Important Words in the Art of Plain and Artistic Painting, with Details of Practice in Coach, Carriage, Railway Car, House, Sign, and Ornamental Painting, including Graining, Marbling, Stnimng, Varnishing, Polishing, Lettering, Stenciling, Gilding, Bronzing, etc. By FRANKLIN 13. GARDNER, 158 Illustrations. I2mo. 427 pp. . . . . " . $2.00 GARDNER. Everybody's Paint Book: A Complete Guide to the Art of Outdoor and Indoor Painting, De- signed for the Special Use of those who wish to do their own work, and consisting of Practical Lessons in Plain Painting, Varnishing, Polishing, Staining, P?prr Hanging, Kalsomining, etc., as well as Directions for Renovating Furniture, and Hints on Artistic Work for Home Decoration. 38 Illustrations. I2mc., 183 pp. . ^$1.00 GEE. The Goldsmith's Handbook: Containing full instructions for the Alloying and Working of Gold, including the Art of Alloying, Melting, Reducing, Coloring, Col lecting, and Refining; the Processes of Manipulation, Recovery of Waste; Chemical and Physical Properties of Gold; with a New System of Mixing its Alloys ; Solders, Enamels, and other Useful Rules and Recipes. By GEORGE E. GEE. 121110. P . #1.25 GEE. The Silversmith's Handbook : Containing full instructions for the Alloying and Working of Silver, including the different modes of Refining -,nd Melting the Metal; its Solders; the Preparation of Imitation Alloys; Methods of Manipula- tion ; Prevention of Waste ; Instructions for Improving and Finishing the Surface of the Work ; together with other Useful Information and Memoranda. By GEORGE E. GEE. Illustrated. I2mo. 1.25 GOTHIC ALBUM FOR CABINET-MAKERS: Designs for Gothic Furniture. Twenty-three plates. Oblong $1.50 3RANT. A Handbook on the Teeth of Gears : Their Curves, Properties, and Practical Construction. By GEORGK B. GRANT. Illustrated. Third Edition, enlarged. 8vo. $i oo GREENWOOD. Steel and Iron: Comprising the Practice and Theory of the Several Methods Pur- sued in their Manufacture, and of their Treatment in the Rolling. Mills, the Forge, and the Foundry. By WILLIAM HENRY GREEN- WOOD, F. C. S. With 97 Diagrams, 536 pages. I2mo. #2.00 HENRY CAREY BAIRD & CO.'S CATALOGUE. GREGORY. Mathematics for Practical Men : Adapted to the Pursuits of Surveyors, Architects, Mechanics, and Civil Engineers. By OLINTHUS GREGORY. 8vo., plates $3.00 GRISWOLD. Railroad Engineer's Pocket Companion for th< Field : Comprising Rules for Calculating Deflection Distances and Angles, Tangential Distances and Angles, and all Necessary Tables for En gineers; also the Art of Levelling from Preliminary Survey to the Construction of Railroads, intended Expressly for the Young En- gineer, together with Numerous Valuable Rules and Examples. By W. GRISWOLU. I2mo., tucks ..... $i.$o GRUNER. Studies of Blast Furnace Phenomena: By M. L. GRUNER, President of the General Council of Mines oi France, and lately Professor of Metallurgy at the Ecole des Mines. Translated, with the author's sanction, with an Appendix, by L. I). B. GORDON, F. R. S. E., F. G. S. 8vo. . . . $2.50 Hand-Book of Useful Tables for the Lumberman, Farmei and Mechanic: Containing Accurate Tables of Logs Reduced to Inch Board Meas. ure, Plank, Scantling and Timber Measure; Wages and Rent, by Week or Month; Capacity of Granaries, Bins and Cisterns; Land Measure, Interest Tables, with Directions for Finding the Interest on any sum at 4, 5, 6, 7 and 8 per cent., and many other Useful Tables. 32 mo., boards. 186 pages .25 HASERICK. The Secrets of the Art of Dyeing Wool, Cotton, and Linen, Including Bleaching and Coloring Wool and Cotton Hosiery and Random Yarns. A Treatise based on Economy and Practice. By E. C. HASERICK. Illustrated by 323 Dyed Patterns of the Yami or fabrics. 8vo $7-5<3 HATS AND FELTING: A Practical Treatise on their Manufacture. By a Practical Hatter. Illustrated by Drawings of Machinery, etc. 8vo. . . $1.25 HOFFER. A Practical Treatise on Caoutchouc and Gulta Percha, Comprising the Properties of the Raw Materials, and the manner or Mixing and Working them ; with the Fabrication of Vulcanized and Hard Rubbers, Caoutchouc and Gutta Pescha Compositions, Water- proof Substances, Elastic Tissues, the Utilization of Waste, etc., eu. From the German of RAIMUND HOFFER. By W. T. BRANNT. Illustrated I2mo. . $2.50 HAUPT. Street Railway Motors: With Descriptions and Cost of Plants and Operation of the Various Systems how in Use. I2mo. ..... $1-75 HENRY CAREY BAIRD & CO.'S CATALOGUE. 15 HAUPT RHAWN. A Move for Better Roads: Essays on Road-making and Maintenance and Road Laws, for which Prizes or Honorable Mention were Awarded through the University of Pennsylvania by a Committee of Citizens of Philadel- phia, with a Synopsis of other Contributions and a Review by the Secretary, LEWIS M. HAUPT, A. M., C. E.; also an Introduction by WILLIAM H. RHAWN, Chairman of the Committee. 319 pages. 8vo. .......... $2.oc HUGHES. American Miller and Millwright's Assistant: By WILLIAM CARTER HUGHES. i2mo $1.50 HULME. Worked Examination Questions in Plane Geomet- rical Drawing : For the Use of Candidates for the Royal Military Academy, Wool- wich ; the Royal Military College, Sandhurst ; the Indian Civil En- gineering College, Cooper's Hill ; Indian Public Works and Tele- graph Departments ; Royal Marine Light Infantry ; the Oxford and Cambridge Local Examinations, etc. By F. EDWARD HULME, F. L. S., F. S. A., Art-Master Marlborough College. Illustrated by 300 examples. Small quarto ...... $2. so JERVIS. Railroad Property: A Treatise on the Construction and Management of Railways; designed to afford useful knowledge, in the popular style, to the holders of this class of property ; as well as Railway Managers, Offi- cers, and Agents. By JOHN B. JERVIS, late Civil Engineer of the Hudson River Railroad, Croton Aqueduct, etc. i2mo., cloth $2.oc KEENE. A Hand-Book of Practical Gauging: For the Use of Beginners, to which is added a Chapter on Distilla tion, describing the process in operation at the Custom-House for ascertaining the Strength of Wines. By JAMES B. KEENE, of H. M. Customs. 8vo. ........ $1.00 KELLEY. Speeches, Addresses, and Letters on Industrial and Financial Questions : By Hox. WILLIAM D. KELLEY, M. C. 544 pages, 8vo. . $2.50 KELLOGG. A New Monetary System : The only means of Securing the respective Rights of Labor and Property, and of Protecting the Public from Financial Revulsions. By EDWARD KELLOGG. Revised from his work on "Labor and other Capital." With numerous additions from his mnnuscript. Edited by MARY KELLOGG PUTNAM. Fifth edition. To which i* added a Biographical Sketch of the Author. One volume, I2mo. Paper cover . . jgl.oo Bound in cloth 1.25 KEMLO. Watch-Repairer's Hand-Book : Being a Complete Guide to the Young Beginner, in Taking Apart, Putting Together, and Thoroughly Cleaning the English Lever and other .Foreign Watches, and all American Watches. By F. KEMLO, Practical Watchmaker. With Illustrations. I2mo. . $1.25 i6 HENRY CAREY BAIRD & CO.'S CATALOGUE. KENTISH. A Treatise on a Box of Instruments, And the Slide Rule ; with the Theory of Trigonometry and Logs rit.hms, including Practical Geometry, Surveying, Measuring of Tim her, Cask and Malt Gauging, Heights, and Distances. By THOMA* KENTISH. In one volume. I2mo. .... $i.oc I ERL. The Assayer's Manual: An Abridged Treatise on the Docimastic Examination of Ores, and Furnace and other Artiticiil Products. By BRUNO KKRL, Professor in the Roval School of Mines. Translated from the German by WILLIAM T. BRANNT. Second American edition, edited with Ex- tensive Additions by F. LYNWOOD GARRISON, Member of the American Institute of Mining Engineers, etc. Illustrated by 87 en- gravings. 8vo $3-OC KICK. -Flour Manufacture. A Treatise on Milling Science and Practice. By FREDERICK KICK Imperial Regierungsrath, Professor of Mechanical Technology in tin. imperial German Polytechnic Institute, Prague. Translated from the second enlarged and revised edition with supplement by H. H. P. POWLES, Assoc. Memb. Institution of Civil Engineers. Illustrated with 28 Plates, and 167 Wood-cuts. 367 pages. 8vo. . #10.00 KINGZETT. The History, Products, and Processes of the Alkali Trade : Including the most Recent Improvements. By CHARLES THOMAS KINGZETT, Consulting Chemist. With 23 illustrations. 8vo. #2.50 LANDRIN. A Treatise on Steel : Comprising its Theory, Metallurgy, Properties, Practical Working, and Use. By M. H. C. LANDRIN, JR. From the French, by A. A. FESQUET. i2mo. . $2.50 LANGBEIN. A Complete Treatise on the Electro-Deposi- tion of Metals : Comprising Electro-Plating and Gnlvanoplastic Operations, the De- position of Metals by the Contact and Immersion Processes, the Color- ing of Metals, the Methods of Grinding and Polishing, as well as Descriptions of the Electric Elemenis, Dynamo-Electric Machines, Thermo- Piles and of the Materials and Processes used in Every De- partment of the Ait. From the German of DR. GEORGE LANGBEIN, with additions by WM. T. BRANNT. Third Edition, thoroughly re- vised and much enlarged. 150 Engravings. 520 pages. 8vo. $4.00 LARDNER. The Steam-Engine : Fof the Use of Beginners. Illustrated. I2mo. 75 LEHNER. The Manufacture of Ink: Comprising the Raw Materials, and the Preparation of Wiling, Copying and Hektograph Inks, Safety Inks, Ink Extracts and Pow- ders, etc. Translated from the German of SlGMUND LEHNER, with additions by WILLIAM T. BRANNT. Illustrated. 12010. HENRY CAREY BAIRD & CO.'S CATALOGUE. 17 LARKIN. The Practical Brass and Iron Founder's Guide: A Concise Treatise on Brass Founding, Moulding, the Metals and their Alloys, etc. ; to which are added Recent Improvements in th Manufacture of Iron, Steel by the Bessemer Process, etc., etc. By TAMES LARKIN, late Conductor of the Brass Foundry Department i& Reany, Neafie & Co.'s Penn Works, Philadelphia. New edition, revised, with extensive additions. I2mo. . . . $2.$& LEROUX. A Practical Treatise on the Manufacture of Worsteds and Carded Yarns : Comprising Practical Mechanics, with Rules and Calculations applied to Spinning; Sorting, Cleaning, and Scouring Wools; the English and French Methods of Combing, Drawing, and Spinning Worsteds, and Manufacturing Carded Yarns. Translated from the French of CHARLES LEROUX, Mechanical Engineer and Superintendent of a Spinning-Mill, by HORATIO PAINE, M. D., and A. A. FESQUET, Chemist and Engineer. Illustrated by twelve large Plates. To which is added an Appendix, containing Extracts from the Reports of the International Jury, and of the Artisans selected by the Committee appointed by the Council of the Society of Arts, London, on Woolen and Worsted Machinery and Fabrics, as exhibited in the Paris UnU versal Exposition, 1867. 8vo. ..... $5.00 LEFFEL. The Construction of Mill-Dams : Comprising also the Building of Race and Reservoir Embankment* and Head-Gates, the Measurement of Streams, Gauging of Water Supply, etc. By JAMES LEFFEL & Co. Illustrated by 58 engravings. 8vo. $2.50 LESLIE. Complete Cookery: Directions for Cookery in its Various Branches. By Miss LESLIE. Sixtieth thousand. Thoroughly revised, with the addition of New Receipts. I2mo. . $1.50 LE VAN. The Steam Engine and the Indicator : Their Origin and Progressive Development ; including the Most Recent Examples of Steam and Gas Motors, together with the Indi- cator, its Principles, its Utility, and its Application. By WILLIAM BARNET LE VAN. Illustrated by 205 Engravings, chiefly of Indi- cator-Cards. 469 pp. 8vo. ...... $4.00 LIEBER. Assayer's Guide : Or, Practical Directions to Assayers, Miners, and Smelters, for the Tests and Assays, by Heat and by Wet Processes, for the Ores of all the principal Metals, of Gold and Silver Coins and Alloys, and of Coal, etc. By OSCAR M. LIEBER. Revised. 283 pp. I2mo. $ 1.50 Lockwood's Dictionary of Terms : Used in the Practice of Mechanical Engineering, embracing those Current in the Drawing Office, Pattern Shop, Foundry, Fitting, Turn- ing, Smith's and Boiler Shops, etc., etc., comprising upwards of Six^ Thousand Definitions. Edited by a Foreman Pattern Maker, author tof " Pattern Making." 417 pp. I2tno. . . . $3.00 HENRY CAREY BAIRD & CO.'S CATALOGUE LUKIN. Amongst Machines: Embracing Descriptions of the various Mechanical Appliances used in the Manufacture of Wood, Metai, and other Substances. i2mo. #1.7* LUKIN. -The Boy Engineers : What They Did, and How They Did It. With 30 plates. i8mo. #i-75 LUKIN. The Young Mechanic t Practical Carpentry. Containing Directions for the Use of all kinds, of Tools, and for Construction of Steam- Engines and Mechanical Models, including the Art of Turning in Wood and Metal. By JOHN LUKIN, Author of "The Lathe and Its Uses," etc. Illustrated. I2mo. . . . . . . . . . . $i-75 MAIN and BROWN. Questions on Subjects Connected with the Marine Steam-Engine : And Examination Papers; with Hints for their Solution. By THOMAS J. MAIN, Professor of Mathematics, Royal Maval College, and THOMAS BROWN, Chief Engineer, R. N. I2mo., cloth . $1.00 MAIN and BROWN. The Indicator and Dynamometer: With their Practical Applications to the Steam-Engine. By THOMAS J. MAIN, M. A. F. R., Ass't S. Professor Royal Naval College, Portsmouth, and THOMAS BROWN, Assoc. Inst. C. E., Chief Engineei R. N., attached to the R. N. College. Illustrated. 8vo. . MAIN and BROWN. The Marine Steam-Engine. By THOMAS J. MAIN, F. R. Ass't S. Mathematical Professor at the Royal Naval College, Portsmouth, and THOMAS BROWN, Assoc. Inst. C. E., Chief Engineer R. N. Attached to the Royal Naval College. With numerous illustrations. 8vo. MAKINS. A Manual of Metallurgy: By GEORGE HOGARTH MAKINS. 100 engravings. Second edition rewritten and much enlarged. I2mo., 592 pages . . $ 3 .00 MARTIN. Screw-Cutting Tables, for the Use of Mechanica) Engineers : Showing the Proper Arrangement of Wheels for Cutting the Threads of Screws of any Required Pitch; with a Table for Making the Uni- versal Gas-Pipe Thread and Taps. By W. A. MARTIN, Engineer. 8vo ........... 50 MICHELL. Mine Drainage: Being a Complete and Practical Treatise on Direct-Acting Under* ground Steam Pumping Machinery. With a Description of a large number of the best known Engines, their General Utility and ihe Special Sphere of their Action, the Mode of their Application, and their Merits compared with other Pumping Machinery. By STEPHEN MlCHELL. Illustrated by 137 engravings. 8vo., 277 pages . &6.OG MOLESWORTH. Pocket-Book of Useful Formulae and Memoranda for Civil and Mechanical Engineers. By GUILFORD L. MOLESWORTH, Member of the Institution of Civil Engineers, Chief Resident Engineer of the Ceylon Railway. Full- in Pocket-book form ...... l.oo HENRY CAREY BAIRD & CO.'S CATALOGUE. 19 MOORE. The Universal Assistant and the Complete Me- chanic : Containing over one million Industrial Facts, Calculations, Receipts^ Processes, Trades Secrets, Rules, Business Forms, Legal Items, Etc., in every occupation, from the Household to the Manufactory. By R. MOORE. Illustrated by 500 Engravings. I2mo. . $2.50 MORRIS. Easy Rules for the Measurement of Earthworks : By means of the Prismoidal Formula. Illustrated with Numerous Wood-Cuts, Problems, and Examples, and concluded by an Exten- sive Table for finding the Solidity in cubic yards from Mean Areas. The whole being adapted for convenient use by Engineers, Surveyors, Contractors, and others needing Correct Measurements of Earthwork. By ELWOOD MORRIS, C. E. 8vo $1.50 MAUCHLINE. The Mine Foreman's Hand-Book Of Practical and Theoretical Information on the Opening, Venti- lating, and Working of Collieries. Questions and Answers on Prac- tical and Theoretical Coal Mining. Designed to Assist Students and Others in Passing Examinations for Mine Foremanships. By ROBERT MAUCHLINE, Ex-Inspector of Mrnes. A New, Revised and Enlarged Edition. Illustrated by 114 engravings. 8vo. 337 Pages $3-75 NAPIER. A System of Chemistry Applied to Dyeing. By JAMES NAPIER, F. C. S. A New and Thoroughly Revised Edi tion. Completely brought up to the present state of the Science, including the Chemistry of Coal Tar Colors, by A. A. FESQUET, Chemist and Engineer. With an Appendix on Dyeing and Calicq Printing, as shown at the Universal Exposition, Paris, 1867. Illus- trated. 8vo. 422 pages $3.00 NEVILLE. Hydraulic Tables, Coefficients, and Formulae, foi finding the Discharge of Water from Orifices, Notches, Weirs, Pipes, and Rivers : Third Edition, with Additions, consisting of New Formulae for the Discharge from Tidal and Flood Sluices and Siphons; general infor- mation on Rainfall, Catchment-Basins, Drainage, Sewerage, Water Supply for Towns and Mill Power. By TOHN NEVILLE, C. E. M. R I. A. ; Fellow of the Royal Geological Society of Ireland. Thicfc I2mo $5.50 NEWBERY. Gleanings from Ornamental Art of every style : Drawn from Examples in the British, South Kensington, Indian, Crystal Palace, and other Museums, the Exhibitions of 1851 and 1862, and the best English and Foreign works. In a series of IOQ exquisitely drawn Plates, containing many hundred examples. B* ROBERT NEWBERY. 410. . . . . . . $12.50 NICHOLLS. The Theoretical and Practical Boiler-Maker and Engineer's Reference Book: Containing a variety of Useful Information for Employers of Labor Foremen and Working Boiler- Makers, Iron, Copper, and Tinsmith* 20 HENRY CAREY BAIRD & CO.'S CATALOGUE. Oranghismen, Engineers, the General Steam-using Public, and for th Use of Science Schools and Classes. By SAMUEL NICHOLLS. Illus- trated by sixteen plates, I2mo. $2.50 NICHOLSON. A Manual of the Art of Bookbinding : Containing full instructions in the different Branches of Forwarding, Gilding, and Finishing. Also, the Art of Marbling Book-edges and Paper. By JAMES B. NICHOLSON. Illustrated. I2mo., cloth $2.25 NICOLLS. The Railway Builder: A Hand-Book for Estimating the Probable Cost of American Rail- way Construction and Equipment. By WILLIAM J. NICOLLS, Civil Engineer. Illustrated, full bound, pocket-book form NORM ANDY. The Commercial Handbook of Chemical An- alysis : Or Practical Instructions for the Determination of the Intrinsic oi Commercial Value of Substances used in Manufactures, in Trades, and in the Arts. By A. NORMANDY. New Edition, Enlarged, and to a great extent rewritten. By HENRY M. NOAD, Ph.D., F.R.S., thick I2mo. . $5.00 N ORRIS. A Handbook for Locomotive Engineers and Ma- chinists : Comprising the Proportions and Calculations for Constructing Loco- motives; Manner of Setting Valves; Tables cf Squares, Cubes, Areas, etc., etc. By SEPTIMUS NORRIS, M. E. New edition. Illustrated, I2mo 1.50 NYSTROM. A New Treatise on Elements of Mechanics : Establishing Strict Precision in the Meaning of Dynamical Terms : accompanied with an Appendix on Duodenal Arithmetic and Me trology. By JOHN W. NYSTROM, C. E. Illustrated. 8vo. $3.00 NYSTROM. On Technological Education and the Construc- tion of Ships and Screw Propellers : For Naval and Marine Engineers. By JOHN W. NYSTROM, Inte Acting Chief Engineer, U. S. N. Second edition, revised, with addi- tional matter. Illustrated by seven engravings. I2mo. . $1-25 O'NEILL. A Dictionary of Dyeing and Calico Printing: Containing a brief account of all the Substances and Processes in use in the Art of Dyeing and Printing Textile Fabrics ; with Practical Receipts and Scientific Information. By CHARLES O'NEILL, Analy- tical Chemist. To which is added an Essay on Coal Tar Colors and their application to Dyeing and Calico Printing. By A. A. FESQUET, Chemist and Engineer. With an appendix on Dyeing and Calico Printing, as shown at the Universal Exposition, Paris, 1867- 8vo.. 491 pages $3.00 ORTON. Underground Treasures'. How and Where to P'ind Them. A Key for the Ready Determination of all the Useful Minerals within the United States. By JAMES ORTON, A.M., Late Professor of Natural History in Vassar College, AJ. Y.; Cor. Mem. of the Academy of Natural Sciences, Philadelphia, and of the Lyceum of Natural History, New York ; author of the "'Andes and the Amazon," etc. A New Edition, with Additions, illustrated $1.59 HENRY CAREY BAIRD & CO.'S CATALOGUE. 21 OSBORN. The Prospector's Field Book and Guide. In the Search For and the Easy Determination of Ores and Other Useful Minerals. By Prof. H. S. OSBORN, LL. D. Illustrated by 58 Engravings. I2mo. Third Edition. Revised ami Enlarged (1897). #1.50 OSBORN A Practical Manual of Minerals, Mines and Min- ing : Comprising the Physical Properties, Geologic Positions, Local Occur- rence and Associations of the Useful Minerals; their Methods of Chemical Analysis and Assay ; together with Various Systems of Ex- cavating and limbering, Brick and Masonry Work, during Driving, Lining, Bracing and other Operations, etc. By Prof. H. S. OSBORN, LL. D., Author of " The Prospector's Field- Book and Guide." 171 engravings. Second Edition, revised. 8vo. . ' . . $4.50 OVERMAN. The Manufacture of Steel: Containing the Practice and Principles of Working and Making Steel. A Handbook for Blacksmiths and Workers in Steel and Iron, Wagon Makers, Die Sinkers, Cutlers, and Manufacturers of Files and Hard- ware, of Slcel and Iron, and for Men of Science and Art. By FREDERICK OVERMAN, Mining Engineer, Author of the " Manu- facture of Lon," etc. A new, enlarged, and revised Edition. By A. A. FESQL,T, Chemist and Engineer. I2mo. . . $1.50 OVERMAN. -The Moulder's and Founder's Pocket Guide : A Treatise or. Moulding and founding in Green-sand, Dry -sand, Loam, and Cement; the Moulding of Machine Frames, Mill-gear, Hollow- ware, Ornaments, Trinkets, Bells, and Statues; Description of Moulds for Iron, Bronze, Brass, and other Metals; Plaster of Paris, Sulphur, Wax, etc. ; the Construction of Melting Furnaces, the Melting and Founding of Metals ; the Composition of Alloys and their Nature, etc., etc. By FREDERICK OVERMAN, M. E. A new Edition, to which is added a Supplement on Statuary and Ornamental Moulding, Ordnance, Malleable Iron Castings, etc. By A. A. FESQUET, Chem- ist and Engineer. Illustrated by 44 engravings. I2mo. . $2.OO PAINTER, GILDER, AND VARNISHER'S COMPANION. Comprising the Manufacture and Test of Pigments, the Arts of Paint- ing, Graining, Marbling, Staining, Sign- writing, Varnishing, Glass- staining, and Gilding on Glass; together with Coach Painting and Varnishing, and the Principles of the Harmony and Contrast of Colors. Twenty-seventh Edition. Revised, Enlarged, and in great part Rewritten. By WILLIAM T. BRANNT, Editor of "Varnishes, Lacquers, Printing Inks and Sealing Waxes." Illustrated. 395 pp. I2mo. .......... $i 50 PALLETT. The Miller's, Millwright's, and Engineer's Guide. By HENRY PALLETT. Illustrated. i2mo. . . . #2.00 22 HENRY CAREY BAIRD & CO.'S CATALOGUE. PERCY. The Manufacture of Russian Sheet-Iron. By JOHN PERCY, M. D., F. R. S., Lecturer on Metallurgy at the Royal School of Mines, and to The Advance Class of Artillery Officers at the Royal Artillery Institution, Woolwich ; Author of " Metallurgy." With Illustrations. 8vo., paper . . 25 cts. PERKINS. Gas and Ventilation : Practical Treatise on Gas and Ventilation. With Special Relation to Illuminating, Heating, and Cooking by Gas. Including Scientific Helps to Engineer-students and others. With Illustrated Diagrams. By E. E. PERKINS. I2mo., cloth $1.25 PERKINS AND STOWE. A New Guide to the Sheet-iron and Boiler Plate Roller : Containing a Series of Tables showing the Weight of Slabs and Pilei to Produce Boiler Plates, and of the Weight of Piles and the Sizes of Bars to produce Sheet-iron; the Thickness of the Bar Gauge in decimals ; the Weight per foot, and the Thickness, on the Bar or Wire Gauge of the fractional parts of an inch; the Weight per sheet, and the Thickness on the Wire Gauge of Sheet-iron of various dimensions to weigh 112 Ibs. per bundle; and the conversion of Short Weight into. Long Weight, and Long Weight into Short. Estimated and collected by G. H. PERKINS and J. G. STOWE. $1.50 POWELL-CHANCE HARRIS The Principles of Glass Making. By HARRY J. POWELL, B. A. Together with Treatises on Crown and Sheet Glass; by HENRY CHANCE, M. A. And Plate Glass, by H. G. HARRIS, Asso. M. Inst. C. E. Illustrated i8mo. . $1.50 PROCTOR. A Pocket-Book of Useful Tables and Formulas for Marine Engineers : By FRANK PROCTOR. Second Edition, Revised and Enlarged. Full -bound pocket-book form ...... $1.50 REGNAULT. Elements of Chemistry: By M. V. REGNAULT. Translated from the French by T. FORREST BETTON, M. D., and edited, with Notes, by JAMES C. BOOTH, Melter and Refiner U. S. Mint, and WILLIAM L. FABER, Metallurgist and Mining Engineer. Illustrated by nearly 700 wood-engravings. Com- prising nearly 1,500 pages. In two volumes, 8vo., cloth . 6.00 RICHARDS. Aluminium : Its History, Occurrence, Properties, Metallurgy and Applications, including its Alloys. By JOSEPH W. RICHARDS, A. C., Chemist and Practical Metallurgist, Member of the Deutsche Chemische Gesell- schaft. Illust. Third edition, enlarged and revised (1895) #6.00 RIFFAULT, VERGNAUD, and TOUSSAINT. A Practical Treatise on the Manufacture of Colors for Painting : Comprising the Origin, Definition, and Classification of Colors; the Treatment of the Raw Materials ; the best Formulae and the Newest Processes for the Preparation of every description of Pigment, and the Necessary Apparatus and Directions for its Use ; Dryers ; thd Testing, Application, and Qualities of Paints, etc., etc. By MM. RIFFAULT, VERGNAUD, and TOUSSAINT. Revised and Edited by M. HENRY CAREY BAIRD & CO.'S CATALOGUE. 23 F. MALEPEYRE. Translated from the French, by A. A. FESQtnriy Chemist and Engineer. Illustrated by Eighty engravings. In one vol., 8vo., 659 pages $$&* ROPER. A Catechism of High- Pressure, or Non-Condensing Steam -Engines : Including the Modelling, Constructing, and Management of Steam- Engines and Steam Boilers. With valuable illustrations. By STE- PHEN ROPER, Engineer. Sixteenth edition, revised and enlarged. i8mo., tucks, gilt edge ....... $2.00 ROPER. Engineer's Handy-Book: Containing a full Explanation of the Steam-Engine Indicator, and its Use and Advantages to Engineers and Steam Users. With Formulae /or Estimating the Power of all Classes of Steam-Engines ; also, Facts, Figures, Questions, and Tables for Engineers who wish to qualify Chemselves for the United States Navy, the Revenue Service, the Mercantile Marine, or to take charge of the Better Class of Sta- tionary Steam-Engines. Sixth edition. l6mo., 690 pages, tucks, gilt edge .......... $3-5 ROPER. Hand-Book of Land and Marine Engines : Including the Modelling, Construction, Running, and Management of Lane* and Marine Engines and Boilers. With frustrations. By STEPHEN ROPER, Engineer. Sixth edition. I2mo.,tx'cks, gilt edge. $3-50 ROPER. Hand-Book of the Locomotive : Including the Construction of Engines and Boilers, and theConstruc- ti ) i, Management, and Running of Locomotives. By STEPHEN ROPER. Eleventh edition. l8mo., tucks, gilt edge . $2.50 ROPER. Hand-Book of Modern Steam Fire-Engines. With illustrations. By STEPHEN ROPER, Engineer. Fourth edition, 1 2ino., tucks, gilt edge ....... $3'$<3 ROPER. Questions and Answers for Engineers. This little book contains all the Questions that Engineers will be asked when undergoing an Examination for the purpose of procuring Licenses, and they are so plain that any Engineer or Fireman of or dinary intelligence may commit them to memory in a short time.. By STEPHEN ROPER, Engineer. Third edition . . . $2.00 ROPER. Use and Abuse of the Steam Boiler. By STEPHEN ROPER, Engineer. Eighth edition, with illustrations. i8mo., tucks, gilt edge $2.00 ROSE. The Complete Practical Machinist : Embracing Lathe Work, Vise Work, Drills and Drilling, Taps and Dies, Hardening and Tempering, the Making and Use of Tools. Tool Grinding, Marking out Work, Machine Tools, etc. By JOSHUA ROSE. 39^ Engravings. Nineteenth Edition, greatly Enlarged with New and Valuable Matter. I2mo., 504 pages. . . $2.50 ROSE. Mechanical Drawing Self-Taught: Comprising Instructions in the Selection and Preparation of Drawing Instruments, Elemental v Instruction in Practical Mechanical Draw- 24 HENRY CAREY BAIRD & CO.'S CATALOGUE. ing, together with Examples in Simple Geometry and Elementary Mechanism, including Screw Threads, Gear Wheels, Mechanical Motions, Engines and Boilers. By JOSHUA ROSE, M. E. Illustrated by 330 engravings. 8vo., 313 pages .... #4.00 ROSE. The Slide- Valve Practically Explained: Embracing simple and complete Practical Demonstrations of th, operation of each element in a Slide-valve Movement, and illustrat- ing the effects of Variations in their Proportions by examples care- fully selected from the most recent and successful practice. By JOSHUA ROSE, M. E. Illustrated by 35 engravings . $1.00 ROSS. The Blowpipe in Chemistry, Mineralogy and Geology : Containing all Known Methods of Anhydrous Analysis, many Work- ing Examples, and Instructions for Making Apparatus. By LIEUT.- COLONEL W. A. Ross, R. A., F. G. S. With 120 Illustrations. I2mo $2.00 SHAW. Civil Architecture : Being a Complete Theoretical and Practical System of Building, con. taining the Fundamental Principles of the Art. By EDWARD SHAW, Architect. To which is added a Treatise on Gothic Architecture, etc. By THOMAS W. SILLOWAY and GEORGE M. HARDING, Architects. The whole illustrated by 102 quarto plates finely engraved on copper. Eleventh edition. 4to. ....... #6.00 SHUNK. A Practical Treatise on Railway Curves and Loca- tion, for Young Engineers. By W. F. SHUNK, C. E. I2mo. Full bound pocket-book form $2.00 SLATER. The Manual of Colors and Dye Wares. By J. W. SLATER. I2mo $3.00 SLOAN. American Houses : A variety of Original Designs for Rural Buildings. Illustrated by 26 colored engravings, with descriptive references. By SAMUEL SLOAN, Architect. 8vo. . . . . . . $ i.oo SLOAN. Homestead Architecture: Containing Forty Designs for Villas, Cottages, and Farm-houses, with Essays on Style, Construction, Landscape Gardening, Furniture, etc., etc. Illustrated by upwards of 200 engravings. By SAMUEL SLOAN, Architect. 8vo $3.00 SLOANE. Hoir>e Experiments m Science. By T. O'CoNOR SLOANE, E. M., A. M., Fh. D. Illustrated by 91 engravings. I2mo. ....... $l.oo SMEATON. Builder's Pocket-Companion : Containing the Elements of Building, Surveying, and Architecture; with Practical Rules and Instructions connected with the subject. By A. C. SMEATON, Civil Engineer, etc. 12010. . 75 cts. SMITH. A Manual of Political Economy. By E. PESHINE SMITH. A New Edition, to which is added a full Index. i2mo. . . $125 HENRY CAREY BAIRD & CO.'S CATALOGUE. 25 SMITH. Parks and Pleasure -Grounds : Or Practical Notes on Country Residences, Villas, Public Parks, and Gardens. By CHARLES H. J. SMITH, Landscape Gardener and Garden Architect, etc., etc. I2mo. .... $2.oa SMITH. The Dyer's Instructor : Comprising Practical Instructions in the Art of Dyeing Silk, Cotton^ Wool, and Worsted, and Woolen Goods; containing nearly 800 Receipts. To which is added a Treatise on the Art of Padding; anc} the Printing of Silk Warps, Skeins, and Handkerchiefs, and the various Mordants and Colors for the different styles of such work. By DAVID SMITH, Pattern Dyer. I2mo. . . . $1.50 SMYTH. A Rudimentary Treatise on Coal and Coal-Mining. By WARRINGTON W. SMYTH, M. A., F. R. G., President R. G. S, of Cornwall. Fifth edition, revised and corrected. With numer- ous illustrations. I2mo. ...... $i7$ SNIVELY. Tables for Systematic Qualitative Chemical AnaK ysis. By JOHN H. SNIVELY, Phr. D. 8vo. . . " . . $1.00 SNIVELY. The Elements of Systematic Qualitative chemical Analysis : A Hand-book for Beginners. By JOHN H. SNIVELY, Phr. D. i6mo. $2.00 STOKES. The Cabinet Maker and Upholsterer's Companion: Comprising the Art of Drawing, as applicable to Cabinet Work; Veneering, Inlaying, and Buhl- Work; the Art of Dyeing and Stain- ing Wood, Ivory, Bone, Tortoise-Shell, etc. Directions for Lacker- ing, Japanning, and Vanishing; to make French Polish, Glues, Cements, and Compos-l.Fns; with numerous Receipts, useful to work men generally. Bv STOKES. Illustrated. A New Edition, with an Appendix upor ,ench Polishing, Staining, Imitating, Varnishing, etc., etc. I2mo ........ $1.25 STRENGTH AND OTHER PROPERTIES OF METALS; Reports of Experiments on the Strength and other Properties of Metals for Cannon. With a Description of the Machines for Testing Metals, and of the Classification of Cannon in service. By Officers of the Ordnance Department, U. S. Army. By authority of the Secre- tary of War. Illustrated by 25 large steel plates. Quarto . $5.00 BULLIVAN. Protection to Native Industry. By Sir EDWARD SULLIVAN, Baronet, author of " Ten Chapters on Social Reforms." 8vo #1.00 BULZ. A Treatise on Beverages : Or the Complete Practical Bottler. Full instructions for Laboratory Work,. with Original Practical Recipes for all kinds of Carbonated Drinks, Mineral Waters, Flavorings, Extracts, Syrups, etc. By CHAS. HERMAN SULZ, Techhical Chemist ana Practical Bottler Illustrated by 428 Engraving*. 8ttf pp. vo . * $10.00 26 HENRY CAREY BAIRb & CO.'S CATALOGUE. SYME. Outlines of an Industrial Science. By DAVID SYME. i2mo. . ... $2.00 TABLES SHOWING THE WEIGHT OF ROUND, SQUARE, AND FLAT BAR IRON, STEEL, ETC., By Measurement. Cloth ...... 63 TAYLOR. Statistics of Coal : Including Mineral Bituminous Substances employed in Arts and Manufactures; with their Geographical, Geological, and Commercial Distribution and Amount of Production and Consumption on the American Continent. With Incidental Statistics of the Iron Manu- facture. By R. C. TAYLOR. Second edition, revised by S. S. HALDE- MAN. Illustrated by five Maps and many wood engravings. 8vo., cloth $6.00 TEMPLETON. The Practical Examinator on Steam and the Steam -Engine : With Instructive References relative thereto, arranged for the Use of Engineers, Students, and others. By WILLIAM TEMPLETON, En- gineer. I2mo. ........ $1.00 THAU SING. The Theory and Practice of the Preparation of Malt and the Fabrication of Beer : With especial reference to the Vienna Process of Brewing. Elab- orated from personal experience by JULIUS E. THAUSING, Professor at the School for Brewers, and at the Agricultural Institute, Modling, near Vienna. Translated from the German by WILLIAM T. BRANNT, Thoroughly and elaborately edited, with much American matter, and according to the latest and most Scientific Practice, by A. SCHWARZ and DR. A. II. BAUER. Illustrated by 140 Engravings. 8vo., 815 pages .......... $10.00 THOMAS. The Modern Practice of Photography: By R. W. THOMAS, F. C. S. 8vo. .... 25 THOMPSON. Political Economy. With Especial Reference f o the Industrial History of Nations : By ROBERT E. THOMPSON, M. A., Professor of Social Science in the University of Pennsylvania. I2mo. . . . . $1.50 THOMSON. Freight Charges Calculator: By ANDREW THOMSON, Freight Agent. 24010. . . $1.25 TURNER'S (THE) COMPANION: Containing Instructions in Concentric, Elliptic, and Eccentric Turn, hig; also various Plates of Chucks, Tools, and Instruments; and Directions for using the Eccentric Cutter, Drill, Vertical Cutter, and Circular Rest; with Patterns and Instructions for working them I2mo. #I.oo TURNING : Specimens of Fancy Turning Executed on the Hand or Foot- Lathe : With Geometric, Oval, and Eccentric Chucks, and Elliptical Cutting Frame. By an Amateur. Illustrated by 30 exquisite Photographs. 4*o. $2.50 HENRY CAREY BAIRD & CO.'S CATALOGUE. VAILE. Galvanized- Iron Cornice-Worker's Manual: Containing Instructions in Laying out the Different Mitres, and Making Patterns for all kinds of Plain and Circular Work. Also Tables of Weights, Areas and Circumferences of Circles, and other Matter calculated to Benefit the Trade. By CHARLES A. VAILE. Illustrated by twenty-one plates. 4to. . . V ' . $S- VILLE. On Artificial Manures : Their Chemical Selection and Scientific Application to Agriculture. A series of Lectures given at the Experimental Farm at Vincennes, during 1867 and 1874-75. By M. GEORGES VILLE. Translated and Edited by WILLIAM CROOKES, F. R. S. Illustrated by thirty-one engravings. 8vo., 450 pages . . ... . : $6.00 VILLE. The School of Chemical Manures : Or, Elementary Principles in the Use of Fertilizing Agents. From the French of M. GEO. VILLE, by A. A. FESQUET, Chemist and En- gineer. With Illustrations. I2mo. .... $1.25 VOGDES. The Architect's and Builder's Pocket- Companion and Price-Book : Consisting of a Shoit but Comprehensive Epitome of Decimals, Duo- decimals, Geometry and Mensuration ; with Tables of United States Measures, Sizes, Weights, Strengths, etc., of Iron, Wood, Stone, Brick, Cement and Concretes, Quantities of Materials in given Sizes and Dimensions of Wood, Brick and Stone; and full and complete Bills of Prices for Carpenter's Work and Painting ; also, Rules for Computing and Valuing Brick and Brick Work, Stone Work, Paint- ing, Plastering, with a Vocabulary of Technical Terms, etc. By FRANK W. VOGDES, Architect, Indianapolis, Ind. Enlarged, revised, and corrected. In one volume, 368 pages, full-bound, pocket-book form, gilt edges $2.00 Cloth . 1.50 VAN CLEVE. The English and American Mechanic : Comprising a Collection of Over Three Thousand Receipts, Rules, and Tables, designed for the Use of every Mechanic and Manufac- turer. By B. FRANK VAN CLEVE. Illustrated. 500 pp. 121110. $2.00 WAHNSCHAFFE. A Guide to the Scientific Examination of Soils : Comprising Select Methods of Mechanical and Chemical Analysii and Physical Investigation. Translated from the German of Dr. F. WAHNSCHAFFE. With additions by WILLIAM T. BRANNT. Illus. trated by 25 engravings. I2mo. 177 pages . . . $1.50 WALL. Practical Graining : With Descriptions of Colors Employed and Tools Used. Illustrated by 47 Colored Plates, Representing the Various Woods Used JK Interior Finishing. By WILLIAM E. WALL. 8vo. . $2.$o WALTON. Coal-Mining Described and Illustrated: By THOMAS H. WALTON, Mining Engineer. Illustrated by 24 large and elaborate Plates, after Actual Workings and Apparatus. #5.oc a8 HENRY CAREY BAIRD & CO.'S CATALOGUE. WARE. The Sugar Beet. Including a History of the Beet Sugar Industry in Europe, Varietier of the Sugar Beet, Examination, Soils, Tillage, Seeds and Sowing Yield and Cost of Cultivation, Harvesting, Transportation, Conserva- tion, Feeding Qualities of the Beet and of the Pulp, etc. By LEWII S. WARE, C. E., M. E. Illustrated by ninety engravings. 8vo. $4.09 WARN. The Sheet-Metal Worker's Instructor: For Zinc, Sheet-Iron, Copper, and Tin-Plate Workers, etc. Contain- ing a selection of Geometrical Problems ; also, Practical and Simple- Rules for Describing the various Patterns required in the different branches of the above Trades. By REUBEN H. WARN, Practical Tin-Plate Worker. To which is added an Appendix, containing Instructions for Boiler-Making, Mensuration of Surfaces and Solids, Rules for Calculating the Weights of different Figures of Iron and" Steel, Tables of the Weights of Iron, Steel, etc. Illustrated by thirty- two Plates and thirty-seven Wood Engravings. 8vo. . $3.00 WARNER. New Theorems, Tables, and Diagrams, for the* Computation of Earth-work : Designed for the use of Engineers in Preliminary and Final Estimates of Students in Engineering, and of Contractors and other non-profes- sional Computers. In two parts, with an Appendix. Part I. A Prac- tical Treatise ; Part II. A Theoretical Treatise, and the Appendix. Containing Notes to the Rules and Examples of Part I.; Explana- tions of the Construction of Scales, Tables, and Diagrams, and a. Treatise upon Equivalent Square Bases and Equivalent Level Heights. The whole illustrated by numerous original engravings, comprising, explanatory cuts for Definitions and Problems, Stereometric Scales and Diagrams, and a series of Lithographic Drawings from Models i Showing all the Combinations of Solid Forms which occur in Railroad Excavations and Embankments. By JOHN WARNER, A. M., Mining- and Mechanical Engineer. Illustrated by 14 Plates. A new, revised and improved edition. 8vo. $4OC WATSON. A Manual of the Hand-Lathe : Comprising Concise Directions for Working Metals of all kinds, Ivory, Bone and Precious Woods; Dyeing, Coloring, and French Polishing; Inlaying by Veneers, and various methods practised to produce Elaborate work with Dispatch, and at Small Expense. By EGBERT P. WATSON, Author of " The Modern Practice of American Machinists and Engineers." Illustrated by 78 engravings. $1.50 WATSON. The Modern Practice of American Machinists and Engineers Including the Construction, Application, and Use of Drills, Lathe Tools, Cutters for Boring Cylinders, and Hollow-work generally , with the most Economical Speed for the same ; the Results verified bj, Actual Practice at the Lathe, the Vise, and on the Floor. Together HENRY CAREY BAIRD & CO.'S CATALOGUE. 29 \vith Workshop Management, Economy of Manufacture, the Steam Engine, Boilers, Gears, Belting, etc., etc. By EGBERT P. WATSON. 1 1 lustra 1 ed by eighty-six engravings. I2mo. . . . $2.50 WATT. The Art of Soap Making : A Practical Hand-Book ot the Manufacture of Hard and Soft Soaps, Toilet Soaps, etc. Fifth Edition, Revised, to which is added an Appendix on Modern Candle Making. By ALEXANDER WATT. 111. I2mo. ......... $3.00 WEATHERLY. Treatise on the Art of Boiling Sugar, Crys- tallizing, Lozenge-making, Comfits, Gum Goods, And other processes for Confectionery, etc., in which are, explained, in an easy and familiar manner, the various Methods of Manufactur- ing every Description of Raw and Refined Sugar Goods, as sold by Confectioners and others. I2mo. ..... $1.50 \\' ILL. Tables of Qualitative Chemical Analysis : \\ uh an Introductory Chapter on the Course of analysis. By Pro- fessor HEINRICH WILL, of Giessen, Germany. Third American, from the eleventh German edition. Edited by CHARLES F. HIMES, Ph. D., Professor of Natural Science, Dickinson College, Carlisle, Pa. 8vo #1.50 'WILLIAMS. On Heat and Steam : Embracing New Views of Vaporization, Condensation and Explo- .sion. By CHARLES WYE \Vn LIAMS, A. I. C. E. Illustrated. 8vo. $2.50 "WILSON. First Principles of Political Economy: With Reference to Statesmanship and the Progress of Civilization. By Professor W. D. WILSON, of the Cornell University. A new and revised edition. I2mo. . . . . . . . $l-S 'WILSON. The Practical Tool Maker and Designer: Comprising a Full Description of the Latest Construction of Tools and Fixtures for Modern Machine Tools. By H. S. WILSON. Illus- trated by about 250 Engravings. 8vo. . . . . $2 50 The work is designed to be an exnos6 of the latest methods for the manufacture of metal goods; and a treatise on fitting the proper tools to modern metal-working machinery for the uniform production of interchangeable work. It includes, among others, the following subjects: Use and abuse of files; Die making for the punching and cutting press, with illustrations of dies for completing complicate i pieces at one stroke of the press ; Tools for making buttons with as- sembling attachments; Coining; Embossing; Cartridge making; Hol- lowware ; Screw Machines; Bolt and rivet headers; Tapping machines; System of making gauges; Drop forging; Manufacture of wire; The drawing of brazed and seamless tubing, and the possibilities of the draw bench; The Fox lathe; Brazing fixtures; Pickling and cleaning conveniences; Reamers; Taps; Dies; Jigs; Milling machine fixtures; Shop secrets, etc. 'WOODS. Compound Locomotives: By ARTHUR TANNATT WOODS. Second edition, revised and enlarged by DAVID LEONARD BARNES, A. M., C. E. 8vo. 330 pp. $3.00 30 HENRY CAREY BAIRD & CO.'S CATALOGUE. WOHLER. A Hand-Bookof Mineral Analysis: By F. WOHLER, Professor of Chemistry in the University of Gottin- gen. Edited by HENRY B. NASON, Professor of Chemistry in the Renssalaer Polytechnic Institute, Troy, New York. Illustrated. I2mo $2.50 WORSSAM. On Mechanical Saws: From the Transactions of the Society of Engineers, 1869. By S. W. WORSSAM, JR. Illustrated by eighteen large plates. 8vo. $1.50 RECENT ADDITIONS. BRANNT. Varnishes, Lacquers, Printing Inks and Sealing - Waxes : Their Raw Materials and their Manufacture, to which is added the Art of Varnishing and Lacquering, including the Preparation of Put- ties and of Stains for Wood, Ivory, Bone, Horn, and Leather. By WILLIAM T. BRANNT. Illustrated by 39 Engravings, 338 pages. I2tno $3.00 BRANNT The Practical Scourer and Garment Dyer: Comprising Dry or Chemical Cleaning ; the Art of Removing Stains , Fine Washing; Bleaching and Dyeing of Straw Hats, Gloves, and Feathers of all kinds; Dyeing of Worn Clothes of all fabrics, in- cluding Mixed Goods, by One Dip; and the Manufacture of Soaps and Fluids for Cleansing Purposes. Edited by WILLIAM T. BRANNT, Editor of "The Techno-Chemical Receipt Book." Illustrated. 203 pages. I2mo. .,.....' $2.00 BRANNT. Petroleum . Its History, Origin, Occurrence, Production, Physical and Chemical Constitution, Technology, Examination and Uses; Together with the Occurrence and Uses of Natural Gas. Edited chiefly from the German of Prof. Hans Hoefer and Dr. Alexander Veith, by WM. T. BRANNT. Illustrated by 3 Plates and 284 Engravings. 743 pp. 8vo. #7-50 BRANNT. A Practical Treatise on the Manufacture of Vine- gar and Acetates, Cider, and Fruit- Wines : Preservation of Fruits and Vegetables by Canning and Evaporation ; Preparation of Fruit-Butters, Jellies, Marmalades, Catchups, Pickles, Mustards, etc. ' Edited from various sources. By WILLIAM T. BRANNT. Illustrated by 79 Engravings. 479 pp. 8vo. $5.00 BRANNT. The Metal Worker's Handy-Book of Receipts and Processes : Being a Collection of Cliemical Formulas and Practical Manipula- tions for the working of all Metals; including the Decoration and Beautifying of Articles Manufactured therefrom, as well as their Preservation. Edited from various sources. By WILLIAM T. BRANNT. Illustrated. I2mo. $2.50 HENRY CAREY BAIRD & CO.'S CATALOGUE. 3I DEITE. A Practical Treatise on the Manufacture cf Per* fumery : Comprising directions for making all kinds of Perfumes, Sachet Powders, Fumigating Materials, Dentifrices, Cosmetics, etc., with a full account of the Volatile Oils, Balsams, Resins, and other Natural and Artificial Perfume-substances, including the Manufacture of Fruit Ethers, and tests of their purity. By Dr. C. DEITE, assisted by L. BORCHERT, F. EICHBAUM, E. KUGLER, H. TOEFFNER, and other experts. From the German, by WM. T. BRANNT. 28 Engrav- ings. 358 pages. 8vo. 13-00 EDWARDS. American Marine Engineer, Theoretical and Practical : With Examples of the latest and most approved American Practice. By EMORY EDWARDS. 85 illustrations. I2mo. . . $2.50 EDWARDS. 900 Examination Questions and Answers: For Engineers and Firemen (Land and Marine) who desire to ob- tain a United States Government or State License. Pocket-book form, gilt edge * . . $1.5 POSSELT. Technology of Textile Design : Being a Practical Treatise on the Construction and Application of Weaves for all Textile Fabrics, with minute reference to the latest Inventions for Weaving. Containing also an Appendix, showing the Analysis and giving the Calculations necessary for the Manufac. tuie of the various Textile Fabrics. By . A. POSSELT, Head Master Textile Department, Pennsylvania Museum and School of Industrial Art, Philadelphia, with over looo illustrations. 292 pages. 410 $5oc POSSELT. The Jacquard Machine Analysed and Explained: With an Appendix on the Preparation of Jacquard Cards, and Practical Hints to Learners of Jacquard Designing. By E. A. POSSELT. With 230 illustrations and numerous diagrams. 127 pp. 4to #3-00 POSSELT. The Structure of Fibres, Yarns and Fabrics: Being a Practical Treatise for the Use of all Persons Employed in the Manufacture of Textile Fabrics, containing a Description of the Growth and Manipulation of Cotton, Wool, Worsted, Silk. Flax, Jute, Ramie, China Grass and Hemp, and Dealing with all Manu- facturers' Calculations for Every Class of Material, also Giving Minute Details for the Structure of all kinds of Textile Fabrics, and an Appendix of Arithmetic, specially adapted for Textile Purposes. ByE. A. POSSELT. Over 400 Illustrations, quarto. . '$$.00 RICH. Artistic Horse-Shoeing: A Practical and Scientific Treatise, giving Improved Methods of Shoeing, with Special Directions for Shaping Shoes to Cure Different Diseases of the Foot, and for the Correction of Faulty Action in Trotters. By GEORGE E. RICH. 62 Illustrations. 153 pages. . I2mo 32 HENRY CAREY BAIRD & CO.'S CATALOGUE. RICH ARDSON. Practical Blacksmithing : A Collection of Articles Contributed at Different Times by Skilled Workmen to the columns of " The Blacksmith and Wheelwright," and Covering nearly the Whole Range of Blacksmithing, from the Simplest Job of Work to some of the Most Complex Forging*. Compiled and Edited by M. T. RICHARDSON. Vol.1. 210 Illustrations. 224 pages. I2mo. . . $1.00 Vol. IT. 230 Illustrations. 262 pages. I2mo. . . $1.00 Vol. III. 390 Illustrations. 307 pages. I2mo. , . $i .00 Vol. IV. 226 Illustrations. 276 pages. lamo. . . $1.00 RICHARDSON. The Practical Horseshoer: Being a Collection of Articles on Horseshoeing in all its Branchei which have appeared from time to time in the columns of " 1 he Blacksmith and Wheelwright," etc. Compiled and edited by M. T. RICHARDSON. 174 illustrations. $1.00 ROPER. Instructions and Suggestions for Engineers and Firemen : By STEPHEN ROPER, Engineer. i8mo. Morocco . #2.00 ROPER. The Steam Boiler: Its Care and Management: By STEPHEN ROPER, Engineer. I2mo., tuck, gilt edges. $2.00 ROPER. The Young Engineer's Own Book: Containing an Explanation of the Principle and Theories on which the Steam Engine as a Prime Mover is Based. By STEPHEN ROPER, Engineer. 160 illustrations, 363 pages. i8mo., tuck . $3.00 ROSE. Modern Steam -Engines: An Elementary Treatise upon the Steam-Engine, written in Plain language ; for Use in the Workshop as well as in the Drawing Office. Giving Full Explanations of the Construction of Modern Steanv Engines : Including Diagrams showing their Actual operation. To- gether with Complete but Simple Explanations of the operations of Various Kinds of Valves, Valve Motions, and Link Motions, etc., thereby Enabling the Ordinary Engineer to clearly Understand the Principles Involved in their Construction and Use, and to Plot out their Movements upon the Drawing Board. By JOSHUA ROSE. M. E. Illustrated by 422 engravings. Revised. 358 pp. . . #6.00 ROSE. Steam Boilers: A Practical Treatise on Boiler Construction and Examination, for the Use of Practical Boiler Makers, Boiler Users, and Inspectors; and embracing in plain figures all the calculations necessary in Designing or Classifying Steam Boilers. By JOSHUA ROSE, M. E. Illustrated by 73 engravings. 250 pages. 8vo $2. 50 6CHRIBER. The Complete Carriage and Wagon Painter: A Concise Compendium of the Art of Painting Carriages, Wagons, and Sleighs, embracing Full Directions in all the Various Branches, including Lettering, Scrolling, Ornamenting, Striping, Varnishing, and Coloring, with numerous Recipes for Mixing Colors. 73 Illus- trations. 177 pp. I2mo 1.00 f*y?M- v / $Hr RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2- month loans may be renewed by calling (510)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date iSl DUE AS STAMPED BELOW OCT 1 6 120,000 (4/94)