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-PILES—MAGNETO- 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<ASTY (REPRODUCTION).
What is understood by galvanoplasty; Copper the most suitable metal
for galvauoplastic purposes ......... 352
Physical properties of copper deposited by electrolysis; Smee's experi-
ments; Von Hiibl's experiments for the determination of the condi-
tions under which deposits with different physical properties are ob-
tained; Classes of processes used in galvanoplasty .... 353
I. GAIVVANOPI,ASTIC DEPOSITION IN THE CEU, APPARATUS.
The cell apparatus ........... 354
Simple apparatus for amateurs; Cell apparatus for the production of
cliches 355
Large apparatus ............ 356
French and German forms of cell apparatus . . . . . . 357
Copper bath for the cell apparatus; Table of the approximate content
of pure crystallized blue vitriol at different degrees Baume, and at
59° F 358
Method of removing an excess of acid from the bath .... 359
CONTENTS. xxiii
PAGE
2. GAI^VANOPIvASTlC DEPOSITION BY THE BATTERY AND DYNAMO-MACHINE.
Arrangement for the employment of external sources of current . . 359
Depositions with the battery; Use of the Daniell and of Bunsen elements;
Coupling of elements ... . ...... . . . 3GO
Depositions with dynamo- machines ; Copper baths for galvanoplastic
depositions with a separate source of current ..... 361
Bath for depositing with the dynamo; Bath for depositing with the bat-
tery; Von Hiibl's observations on the elasticity, strength and hardness
of galvanoplastic deposits of copper; Most suitable solution for copper
printing plates; Current-density for baths at rest and in motion . . 362
Disadvantage of the difference in composition of the upper and lower
layers of the bath . . ... . . . ... 363
Various methods of effecting the agitation of the bath .... 364
Anodes used, and their surfaces in proportion to that of the cathodes;
Determination of free acid . . . . . . • . . . 365
Determination of the content of copper according to Haen . . . 366
Preparation of moulds (matrices) in plastic material; Moulding in gutta-
percha ... ....... . -. . . . . . 367
The toggle press ... . . - . ... ... 368
Hydraulic press . . . « . . -» . . . . . 369
Moulding in wax (stearine); Various wax mixtures. . : . . . 370
Preparation of the wax mould . . . . . . .... 371
Black-leading, and black-leading machines ; Silas P. Knight's process
of black-leading . ... 372
Preliminary coating of the black-leaded surface with copper ; Gilt and
silvered black-lead . . . . . 373
Wiring the mould; The electric-connection gripper 374
Suspension of the moulds in the bath; Chief requsite for the production
of a dense, coherent and elastic deposit ; Strength of the sulphuric
acid for filling the clay cells . . . __ . . . . . 375
Most suitable current-density for the production of a good deposit;
Coupling of the elements . .'- . . . . . 376
Controlling the current by the resistance board ; Time required for a
sufficiently heavy deposit; Accumulators and their use ... 377
Electro-chemical process of forming storage batteries; Diagram showing
connections of a plant as installed by the Electro-Chemical Storage
Battery Co. , of New York . 378
Detaching the deposit from the mould; Backing the deposit or shell . 380
Finishing; The saw table; Types of power planing or shaving machines. 382
Mounting the plates ; Book plates ; Process of making a copy directly
from a metallic surface without the interposition of wax or gutta-
percha ..... . 383
Electro-etching . ....'...-... t . . . 385
Composition for etching ground; Preparation of printing plates in relief. 386
xxiv CONTENTS.
PAGE
Heliography .... 387
Galvanoplastic reproduction of busts, vases, etc.; Materials for the
moulds . . . .388
Dissection of objects; Moulding round articles in gutta-percha; Metallic
alloys for the preparation of moulds 389
Moulding with metallic alloys ; Taking casts from metallic coins and
medals in plaster of Paris ...... ... 390
Casts from large plastic objects with undercut surfaces and reliefs in
plaster of Paris 391
Making plaster of Paris moulds impervious to fluids .... 392
Making the moulds conductive; Metallization by the wet way . . 393
Parke's and various other methods of metallization by the wet way . 394
Metallization by metallic powders . . . . . . . . 395
Ivenoir's process— galvanoplastic method for originals in high relief;
Gelatine moulds, and their preparation 396
Brandley's directions for preparing gelatine moulds ; Special uses of
galvanoplasty ; Nature printing ... . . . . . 397
Philipp's process for coating laces and tissues with copper, and then sil-
vering or gilding ; Corvin's niello ........ 398
Coating grasses, leaves, flowers, etc., with copper and then silvering,
gilding or platinizing ; Plates for the production of imitations of
leather ; To coat wood, etc., with a galvanoplastic deposit of copper . 399
To protect wooden handles of surgical instruments, etc., from the attacks
of the acid copper bath ; Copper deposit for the mercury vessels of
thermometers ; Metallization of glass, porcelain, clay, terra cotta, etc. ;
Galvanoplastic operations in iron 400
Galvanoplastic operations in nickel . . . . . . . . 401
Galvanoplastic operations in silver and gold ...... 402
Bath for galvanoplastic operations with silver ; Bath for galvanoplastic
operations with gold . . . . . . . . . . 403
CHAPTER XV.
COLORING, PATINIZING ; OXIDIZING, ETC. OF METALS.— LACQUERING.
What is understood by patina and patinizing; Coloring of copper; Shades
from the pale-red of copper to a dark chestnut-brown .... 403
Brown color upon copper ; Method used in the Paris Mint ; Bronze-like
color on copper ... . . . . . . . . 404
Red-brown color on copper ; To color copper blue-black ; Cuivre fum6;
Black color on copper ; Dead-black on copper 405
Solution for obtaining a deep black color on copper; Imitation of genu-
ine patina 406
Steel-gray color upon copper ; Coloring copper dark steel-gray ; Vari-
ous colors upon massive copper, brass and nickel .... 407
CONTENTS. XXV
Coloring of brasses and bronzes; Lustrous black on brass; Steel-gray on
brass 408
Gray color with a bluish tint on brass ; Pale gold color on brass ; Straw
color, to brown, through golden yellow, and tombac color on brass ;
Color resembling gold on brass ........ 409
Brown color, called bronze Barbedienne, on brass ; Coloring bronze
articles dead-yellow or clay-yellow to dark brown .... 410
Smoke bronze ; Violet- and corn-flower blue on brass ; Ebermayer's ex-
periments in coloring brass ......... 411
Coloring zinc ; Experiments in coloring zinc black; Blue-black on zinc;
Gray coating on zinc ; Bronzing on zinc ...... 413
Red-brown color on zinc ; Yellow-brown shades on zinc ; Coloring of
iron ; Lustrous black on iron ......... 414
Meritens's process for obtaining a bright black color on iron . . . 415
Durable blue on iron ; Brown-black coating with bronze lustre on iron ;
To give iron a silvery appearance with high lustre ; Coloring of tin ;
Bronze-like patina on tin ; Durable and very warm sepia-brown tone
upon tin and its alloys ; Dark coloration on tin 416
Coloring of silver ; Lacquering ; Use of lacquers in the electro-plating
industry ; Application of lacquers ; Cellulose lacquers and varnishes ;
Zapon 417
Kristaline; Preparation of a lacquer similar to zapon or kristaline . .418
Operations of gold varnishers . . . . . . . . . 419
Varnishes at the disposal of gold varnishers ; Resinous substances and
tinctorial matters used in the manufacture of varnish ; Removal of
varnish from imperfectly varnished objects 420
CHAPTER XVI.
HYGIENIC RUI,ES FOR THE WORKSHOP.
Neutralization of the action of acid upon the enamel of the teeth and
the mucuous membranes of the mouth and throat; Protection against
the corrosive effect of lime and caustic lyes; Vessels used in the estab-
lishment not to be used for drinking purposes ..... 421
Precautions in handling potassium cyanide and its solutions; Sensitive-
ness of many persons to nickel solutions; Poisoning by hydrocyanic
(prussic) acid, potassium cyanide, or cyanides ..... 422
Remedies to be applied; Poisoning by copper salts, by lead salts, by
arsenic, by alkalies, by mercury salts, sulphuretted hydrogen, and by
chlorine, sulphurous acid, nitrous and hyponitric gases, and remedies. 423
XXVI CONTENTS.
CHAPTER XVII.
CHEMICAL PRODUCTS AND VARIOUS APPARATUS AND INSTRUMENTS USED
IN ELECTRO-PLATING.
A. CHEMICAL PRODUCTS.
PAGE
I. Acids.
Sulphuric acid (oil of vitriol) and its recognition ..... 424
Nitric acid (aqua fortis, spirit of nitre); Hydrochloric acid (muriatic
acid) and their recognition ......... 425
Hydrocyanic acid (prussic acid); Citric acid; Boric acid (boracic acid),
and their recognition 426
Arsenious acid (white arsenic, arsenic, ratsbane); Chromic acid, and
their recognition 427
Hydrofluoric acid and its recognition 428
II. Alkalies and Alkaline Earths.
Potassium hydrate (caustic potash); Sodium hydrate (caustic soda) . 428
Ammonium hydrate (ammonia or spirits of hartshorn), and its recogni-
tion; Calcium hydrate (burnt or quick lime) 429
III. Sulphur Combinations.
Sulphuretted hydrogen (sulphydric acid, hydrosulphuric acid), and its
recognition ............ 429
Potassium sulphide (liver of sulphur) and its recognition; Ammonium
sulphide (sulphydrate or hydrosulphate of ammonia); Carbon disul-
phide or bisulphide; Antimony sulphide; Black sulphide of antimony
(stibium sulfuratum nigruwi}\ Red sulphide of antimony {stibium
sulfuralum aurantiacum} ......... 430
Arsenic trisulphide or arsenious sulphide (orpiment); Ferric sulphide . 431
IV. Chlorine Combinations.
Sodium chloride (common salt, rock salt) and its recognition; Ammon-
ium chloride (sal ammoniac) and its recognition; Antimony trichlor-
ide (butter of antimony) 431
Arsenious chloride; Copper chloride; Tin chloride; Stannous chloride
or tin salt, and its recognition; Stannic chloride; Zinc chloride (hydro-
chlorate or muriate of zinc, butter of zinc) and its recognition . . 432
Zinc chloride and ammonium chloride; Nickel chloride, and its recog-
nition; Cobalt chloride, and its recognition; Silver chloride (horn sil-
ver), and its recognition . ......... 433
Gold chloride (terchloride of gold, muriate of gold, auric chloride), and
its recognition; Platinic chloride or hydroplatinic chloride, and its re-
cognition ............. 434
CONTENTS. XXV11
V. Cyanides.
Potassium cyanide (white prussiate of potash) . . . . ' -. . 435
Recognition of potassium cyanide; Comparative table of potassium cya-
nide with a different content; Copper cyanides, and their recognition. 436
Zinc cyanide (hydrocyanate of zinc, prussiate of zinc), and its recogni-
tion; Silver cyanide (prussiate, or hydrocyanate of silver); Potassium
ferro-cyanide (yellow prussiate of potash), and its recognition . . 437
VI. Carbonates.
Potassium carbonate (potash) and its recognition ; Acid potassium car-
bonate or monopotassic carbonate, commonly called bicarbonate of
potash; Sodium carbonate (washing soda) ...... 438
Sodium bicarbonate (baking powder) ; Calcium carbonate (marble,
chalk); Whiting; Copper carbonate, and its recognition; Zinc car-
bonate, and its recognition ......... 439
Nickel carbonate, and its recognition; Cobalt carbonate. . . . 440
*
VII. Sulphates and Sulphites.
Sodium sulphate (Glauber's salt); Ammonium sulphate, and its recog-
nition; Aluminium-potassium sulphate (potash-alum), and its recog-
nition . . . . . . . . . . . . 440
Iron sulphate (iron protosulphate, ferrous sulphate or green vitriol), and
its recognition; Iron-ammonium sulphate; Copper sulphate (cupric
sulphate or blue vitriol), and its recognition. . . . . . 441
Cuprous sulphite ; Zinc sulphate (white vitriol), and its recognition ;
Nickel sulphate, and its recognition . . . . .. . . 442
Nickel-ammonium sulphate; Cobalt sulphate and its recognition; Cobalt-
auimoniuni sulphate; Sodium sulphite and bisulphite .... 443
VIII. Nitrates.
Potassium nitrate (saltpetre, nitre), and its recognition; Sodium nitrate
(cubic nitre or Chile saltpetre); Mercurous nitrate . . . .444
Mercuric nitrate, and its recognition; Silver nitrate (lunar caustic), and
its recognition . . . . — . ..... . . . 445
IX. Phosphates and Pyrophosphates.
Sodium phosphate, and its recognition; Sodium pyrophosphate, and its
recognition; Ammonium phosphate . . . .- . . . 446
X. Salts of the Organic Acids.
Potassium bitartrate (cream of tartar) » . 446
Potassium sodium tartrate (Rochelle or Seignette salt), and its recogni-
tion; Antimony-potassium tartrate (tartar emetic), and its recognition;
Copper acetate (verdigris); Lead acetate (sugar of lead), and its re-
cognition . . . , .r • . . . . . . . . 447
Sodium citrate . . . . « . . . . . 448
XXVlii CONTENTS.
PAGE
B. VARIOUS APPARATUS AND INSTRUMENTS.
Glass balloons and flasks; Evaporating dishes or capsules; Glass jars . 448
Crucibles ; Hydrometers . 449
Table showing readings of different hydrometers ..... 450
Filters .451
Siphons . . . . . . 452
Stirring rods ............ 453
APPENDIX.
Check voltmeter 454
The Bossard mechano-electroplating tanks ; The long tank . . . 455
Manipulation of the long tank . . . . . . . . 456
The circular tank ........... 457
Advantages claimed for the mechano-electroplating tanks . . . 460
Useful tables ; Table of elements with their symbols, atomic weights,
and specific gravities . .... . . . . . 461
Table of chemical and electro-chemical equivalents; Explanation of the
table . . ... 462
Table showing the value of equal current volumes as expressed in am-
peres per square decimetre, per square foot and per square inch of
electrode surface . . . ... . . . . . 463
Explanation of the table ; Table showing the specific electric resistances
of different sulphuric acid solutions of various temperatures ; Table
showing the specific electric resistances of different copper sulphate
solutions at various temperatures 464
Table of electro-motive force of elements 465
Table showing the solubility of various substances ; Table showing the
composition of the most usual alloys and solders 466
Alloys . . . . 467
Solders ; Hard solder ; Silver solder . . . . . . . .468
Gold solder; Table of melting points of some metals; Table of high
temperatures ; Table of the specific gravity and content of solutions
of potassium carbonate at 57.2° F. ....... 469
Table showing the specific gravity of sulphuric acid at 59° F. . . 470
Table of specific gravity and content of nitric acid ; Table showing the
specific gravity of sal ammoniac solutions at 66.2° F. .... 471
Table showing the electrical resistance of pure copper wire of various
diameters ; Resistance and conductivity of pure copper at different
temperatures 472
Table showing actual diameters in decimal parts of an inch correspond-
ing to the numbers of various wire gauges ...... 473
CONTENTS. XXIX
PAGE
Weight of iron, copper, and brass wire and plates 474
Rules for speed ; To find speed of countershaft in accordance with main
shaft and machine; Example; To find diameter of pulley on the main
shaft ; Example ; To find diameter of pulley on counter-shaft carry-
ing belt to machine ; Example ; To find the speed of a machine . 475
Comparison of the scales of the Fahrenheit, Centigrade, and Reaumur
thermometers, and rules for converting one scale into another . . 476
Index . . . 477
ELECTRO-DEPOSITION OF METALS.
L
HISTORICAL PART.
CHAPTER I.
HISTORICAL REVIEW OF ELECTRO-METALLURGY.
IN reviewing the history of the development of electrolysis,
i. e.y the reduction of a metal or a metallic alloy from the solu-
tion of its salts by the electric current, the simple reduction
which takes place by the immersion of one metal in the solution
of another, may be omitted. This mode of reduction was well
known to the alchemist Zozimus, who described the reduction of
copper from its solutions by means of iron, while Paracelsus
speaks of coating copper and iron with silver by simple immer-
sion in a solution of silver.
Before the discovery, in 1789, of contact-electricity by Luigi
Galvani, there was nothing like a scientific reduction of metal
by electricity; and only in 1799 did Alexander Volta, of
Pavia, succeed in finding the true causes of Galvani's discovery.
Galvani observed while dissecting a frog on a table, whereon
stood an electric machine, that the limbs suddenly became con-
vulsed by one of his pupils' touching the crural nerve with the
dissecting-knife at the instant of taking a spark from the con-
ductor of the machine. The experiment was several times
repeated, and it was found to answer in all cases when a metallic
2 ELECTRO-DEPOSITION OF METALS.
conductor was connected with the nerve, but not otherwise. He
observed that muscular contractions were produced by forming
a connection between two different metals, one of which was
applied to the nerve, and the other to the muscles of the leg.
Similar phenomena having been found to arise when the leg of
the frog was connected with the electric machine, it could
scarcely be doubted that in both cases the muscular contrac-
tions were produced by the same agent. From a course of
experiments, Galvani drew the erroneous inference that these
muscular contractions were caused by a fluid having its seat in
the nerves, which through the metallic connections flowed over
upon the muscles. Everywhere, in Germany, England and
France, eminent scientists hastened to repeat Galvani's experi-
ments, in the hope of discovering in the organism a fluid which
they considered the vital principle ; but it was reserved to Volta
to throw light upon the prevailing darkness. In his repeated
experiments this eminent philosopher observed that one cir-
cumstance had been entirely overlooked, namely, that in order
to produce strong muscular contractions in the frog-leg experi-
ment it was absolutely necessary for the metallic connection to
consist of two different metals coming in contact with each
other. From this he drew the inference that the agent pro-
ducing the muscular contractions was not a nerve-fluid, but was
developed by the contact of dissimilar metals, and identical
with the electricity of the electric machine.
This discovery led to the construction of what is known as
the pile of Volta, or the voltaic pile. The same philosopher
found that the development of electricity could be increased by
building up in regular order a pile of pairs of plates of dissimi-
lar metals, each pair being separated on either side from the
adjacent pairs by pieces of moistened card-board or felt. On
account of various defects of the voltaic pile, Cruikshank soon
afterwards devised his well-known trough battery, which con-
sisted of square plates of copper and zinc soldered together,
and so arranged and fastened in parallel order in a wooden box,
that between each pair of plates a sort of trough was formed,
which was filled with acidulated water.
HISTORICAL REVIEW OF ELECTRO-METALLURGY. 3
Nicholson and Carlisle, on May 2, 1800, first decomposed
water into hydrogen and oxygen by electrolysis ; and, in 1801,
Wollaston found that if a piece of silver in connection with a
more positive metal, for instance, zinc, be put into a solution of
copper, the silver will be coated over with copper, which coat-
ing will stand the operation of burnishing.
Cruikshank, in 1803, investigated the behavior of solutions
of nitrate of silver, sulphate of copper, acetate of lead, and sev-
eral other metallic salts, towards the galvanic current, and found
that the metals were so completely reduced from their solutions
by the current as to suggest to him the analysis of minerals by
means of the electric current.
To Brugnatelli we owe the first practical results in electro-
gilding. In 1805, he gilded two silver medals by connecting
them by means of copper wire with the negative pole of the
pile, and allowing them to dip in a solution of fulminating gold
in potassium cyanide, while a piece of metal was suspended in
the solution from the positive pole. He also observed that the
positive plate, if it consisted of an oxidizable metal, was dis-
solved.
One of the greatest discoveries connected with the subject,
however, is that of Sir Humphry Davy, made October 6, 1807,
when, by the decomposition of the alkalies by means of the
electric current, he discovered the metals potassium and sodium.
Prof. Oersted, of Copenhagen, in 1820, found that the mag-
netic needle is deflected from its direction by the electric cur-
rent. It was known long before this that powerful electric dis-
charges affect the magnetic needle ; it had, for instance, been
observed that the needle of a ship's compass struck by light-
ning had lost its property of indicating the North Pole, and
several physicists, among them Franklin, had succeeded in pro-
ducing the same phenomena by heavy discharges of the elec-
trical machine, but they were satisfied with the supposition that
the electric current acted mechanically, like the blow of a
hammer. Oersted first perceived that electricity must be in a
state of motion in order to act upon magnetism. This led to
4 ELECTRO-DEPOSITION OF METALS.
the construction of the galvanoscope or galvanometer, an in-
strument which indicates whether the elements or other source
of current furnish a current or not, and by which the intensity
of the source of current may also to a certain degree be recog-
nized.
Ohm, in 1827, discovered the law named after him, that the
strength of a continuous current is directly proportional to the
difference of potential or electro-motive force in the circuit, and
inversely proportioned to the resistance of the circuit. This law
will be more fully discussed in the theoretical part.
Ohm's discovery was succeeded, in 1831, by the important
discovery of electric induction by Faraday. By induction is un-
derstood the production of an electric current in a closed circuit
which is in the immediate neighborhood of a current-carrying
wire. Faraday further found that the current induced in the
neighboring wire is not constant, because after a few oscilia-
tions the magnetic needle returned to the position occupied by
it before a current was passed through the current-carrying
wire ; whilst when the current was broken the needle deflected
in the opposite direction.
In the year following the discovery of Faraday, Pixii, of
Paris, constructed the first electro-magnetic induction machine.
Faraday's electrolytic law of the proportionality of the cur-
rent-strength and its chemical action, and that the quantities of
the various substances which are reduced from their combina-
tions by the same current are proportional to their chemical
equivalents, was laid down and proved in 1833, and upon this
Faraday based the measurement of the current-strength by
chemical deposition, as, for instance, that of water, in the
voltmeter.
Of the practical electro-chemical discoveries there remain to
be mentioned the production of iridescent colors, in 1826, by
Nobili, and the production of the amalgams of potassium and
sodium, in 1853, by Bird.
The actual galvanoplastic process, however, dates from the
year 1838. In the spring of 1838, Prof. Jacoby announced to
HISTORICAL REVIEW OF ELECTRO-METALLURGY. 5
the Academy of Sciences of St. Petersburg, a description of his
discovery of the utility of galvanic electricity as a means of re-
producing objects of metal. Hence Jacoby must be considered
the father of galvanoplasty in as far as he was the first to utilize
and give practical form to the discoveries made up to that time.
Though Jacoby's process was published in the English periodi-
cal, "The Athenaeum/' of May 4, 1839, Mr. T. Spencer, who
read a paper on the same subject, September 13,1 839, before the
Liverpool Polytechnic Society, claimed priority of invention, as
was also done by Mr. C. J. Jordan, who, on May 22, 1839, sent
a letter to the " London Mechanical Magazine," which was pub-
lished on June 8, 1839.
From this time forward the galvanoplastic art made rapid
progress, and by the skill and enterprise of such men as the
Elkingtons, of Birmingham, and De Ruolz, of Paris, it was
speedily added to the industrial arts.
Though copies of a metallic object by means of galvanoplasty
could now be made, the employment of the process was re-
stricted to metallic objects of a form suitable for the purpose,
until, in 1840, Murray succeeded in making non-metallic sur-
faces conductive by the application of graphite (black lead,
plumbago), which rendered the production of galvanoplastic
copies of wood-cuts, plaster-of-Paris casts, etc., possible.
Dr. Montgomery, in 1843, sent to England samples of gutta-
percha, which was soon found to be a suitable material for the
production of negatives of the original models to be reproduced
by galvanoplasty.
Though it was now understood how to produce heavy de-
posits of copper, those of gold and silver could only be obtained
in very thin layers, Scheele's observations on the solubility of
the cyynide combinations of gold and silver in potassium
cyanide, led Wright, a co-worker of the Elkingtons, to employ,
in 1840, such solutions for the deposition of gold and silver,
and it was found that deposits produced from these solutions
could be developed to any desired thickness. The use of solu-
tions of metallic cyanides in potassium cyanide prevails at the
6 ELECTRO-DEPOSITION OF METALS.
present time, and the results obtained thereby have not been
surpassed by any other practice.
From the same year also dates the patent for the deposition
of nickel from solution of nitrate of nickel, which, however, did
not attract any special attention. This may have been chiefly
due to the fact that the deposition of nickel from its nitrate
solution is the most imperfect and the least suitable for the
practice.
To Mr. Alfred Smee we owe many discoveries in the deposi-
tion of antimony, platinum, gold, silver, iron, lead, copper, and
zinc. In publishing his experiments, in 1841, he originated
the very appropriate term "electro-metallurgy" for the process
of working in metals by means of electrolysis.
Prof. Bcettger, in 1842, pointed out that dense and lustrous
depositions of nickel could be obtained from its double salt,
sulphate of nickel with sulphate of ammonium, as well as from
ammoniacal solution of sulphate of nickel ; and that such de-
posits, on account of their slight oxidability, great hardness,
and elegant appearance, were capable of many applications.
However, Bcettger' s statements fell into oblivion, and only in
later years, when the execution of nickeling was practically
taken up in the United States, his labors in this department
were remembered in Germany. To Bcettger we are also in-
debted for directions for coating metals with iron, cobalt,
platinum, and various patinas.
In the same year, De Ruolz first succeeded in depositing
metallic alloys — for instance, brass — from the solutions of the
mixed metallic salts. In 1843 the first use of thermo-electricity
appears to have been made by Moses Poole, who took out a
patent for the use of a thermo-electric pile instead of a voltaic
battery for depositing purposes.
From this time forward innumerable improvements in exist-
ing processes were made ; and also the first endeavors to apply
Faraday's discoveries to practical purposes.
The invention of depositing metals by means of a permanent
current of electricity obtained from steel magnets was perfected
.
HISTORICAL REVIEW OF ELECTRO-METALLURGY. *]
and first successfully worked by Messrs. Prime & Son, at their
large silverware works, Birmingham, England, and the original
machine, constructed by Woolrych in 1844 — the first magnetic
machine that ever deposited silver on a practical scale — is still
preserved at their works in its original position as a valuable and
interesting relic. The Woolrych machine stands 5 feet high, 5
feet long, and 2^ feet wide. An illustration of this original
electro-plating machine, kindly furnished us by the Hanson &
Van Winkle Co., of Newark, N. J., is given in Fig. I.
FIG. i.
As early as 1854, Christofle & Co. endeavored to replace their
batteries by magneto-electrical machines, and used the Holmes
type, better known as the Alliance Machine, which, however, did
not prove satisfactory ; and besides, the prices of these machines
were in comparison with their efficacy exorbitant. The ma-
8 ELECTRO-DEPOSITION OF METALS.
chine constructed by Wilde proved objectionable on account of
its heating while working, and the consequent frequent inter-
ruptions in the operations.
In 1860 Dr. Antonie Pacinotti, of Pisa, suggested the use of
an iron ring wound round with insulated wire, in place of the
cylinder. This ring, named after its inventor, has, with more or
less modifications, become typical of many machines of modern
construction. In the construction of all older machines, steel
magnets had been used, and their magnetism not being con-
stant, the effect of the machine was consequently also not
constant. Furthermore, they generated alternately negative
and positive currents, which, by means of commutators, had to
be converted into currents of the same direction ; and this, in
consequence of the vigorous formation of sparks, caused the
rapid wearing out of the commutators.
These defects led to the employment of continuous mag-
netism in the iron cores of the electro-magnets, the first
machine based upon this principle being introduced in 1866,
by Siemens, which, in 1867, was succeeded by Wheatstone's.
However, the first useful machine was introduced in 1871,
by Zenobe Gramme, who in its construction made use of Paci-
notti's ring. This machine was, in 1872, succeeded by Hefner-
Alteneck's, of Berlin. In both machines the poles of the elec-
tro-magnet exert an inducing action only upon the outer wire
wrappings of the revolving ring, the other portions being
scarcely utilized, which increases the resistance and causes a
useless production of heat. This defect led to the construction
of flat- ring machines, in which the cylindrical ring is replaced
by one of a flat shape, and of larger diameter, thus permitting
the induction of both flat sides. Such a machine was, in 1884,
built by Siemens & Halske, of Berlin ; and in the same year by
S. Schuckert, of Niirenberg. In Schuckert's modern machines
nearly three-quarters of all the wire wrappings are under the
inducing influence of both of the large pole shoes of the electro-
magnets.
Of other constructions of dynamo-electrical machines maybe
HISTORICAL REVIEW OF ELECTRO-METALLURGY. 9
mentioned Mather's, Elmore's, Fein's, Mohring's, Krottlinger's,
and Lahmeyer's, the latter especially being at the present time
much employed in Germany for electro-plating purposes. In
this country Weston's machine and the dynamos manufactured
by the Hanson & Van Winkle Co., of Newark, N. J., the Zucker
& Levett Chemical Co., of New York, and others are largely
used for electro-plating purposes.
For the sake of completeness, there may be mentioned the
investigators and practitioners who during the last twenty years
have contributed much to the improvement of the electro-
chemical processes and the perfection of galvanoplasty. Be-
sides those already named, they are: Elkington, Becquerel,
Heeren, Roseleur, Eisner, von Leuchtenberg, Meidinger, Weil,
Goode, Christofle, Klein, von Kress, Thompson, Adams, Giaffe,
and others.
II.
THEORETICAL PART,
CHAPTER II.
MAGNETISM AND ELECTRICITY.
i. MAGNETISM.
FOR the better understanding of the electrolytic laws it will
be necessary to commence with the phenomena presented by
magnetism, and to consider them more closely.
A particular species of iron ore is remarkable for its property
of attracting small pieces of iron and causing them to adhere to
its surface. This iron ore is a combination of ferric oxide with
ferrous oxide (Fe3O4), and is called loadstone or magnetic iron
ore. Its properties were known to the ancients, who called it
magnesian stone after Magnesia, a city in Thessaly, in the
neighborhood of which it was found. If a natural loadstone be
rubbed over a bar of steel, its characteristic properties will be
communicated to the bar, which will then be found to attract
iron filings like the loadstone itself. The bar of steel thus
treated is said to be magnetized, or to constitute an artificial
magnet. The artificial magnets thus produced may be straight
in the shape of a horseshoe, or annular ; but no matter what
their form, the attractive force will appear to be greatest at two
points situated near the extremities of the bar, and least of all
towards the middle. The points of the magnet showing the
greatest attractive force are called the magnetic poles, whilst the
line between them, possessing little or no attractive force, is
termed the neutral line or neutral zone. In a closed magnet the
(10)
MAGNETISM AND ELECTRICITY. I I
poles are situated on the ends of one and the same diameter,
while the neutral zones are located on the ends of a diameter
standing perpendicular to the first.
When a magnetized bar or natural magnet is suspended at
its centre in any convenient manner, so as to be free to move
in a horizontal plane, it is always found to assume a particular
direction with regard to the earth, one end pointing nearly
north and the other nearly south. If the bar be removed from
this position it will tend to reassume it, and after a few oscilla-
tions, settle at rest as before. The direction of the magnetic
bar, i. e., that of its longitudinal axis, is called the magnetic me-
ridian, while the pole pointing towards the north is usually dis-
tinguished as the north pole of the bar, and that which points
southward as the south pole.
A magnet, either natural or artificial, of symmetrical form,
suspended in the presence of a second magnet, serves to ex-
hibit certain phenomena of attraction and repulsion, which
deserve particular attention. When a north pole is presented
to a south pole, or a south pole to a north, attraction ensues
between them ; the ends of the bar approach each other, and,
if permitted, adhere with considerable force. When, on the
other hand, a north pole is brought near a second north pole,
or a south pole near another south pole, mutual repulsion is
observed, and the ends of the bar recede from each other as far
as possible. Poles of an opposite name attract, and poles of a
similar name repel each other.
According to the theory or hypothesis proposed by Ampere,
magnetism is caused by the presence of electric currents in the
ultimate particles of matter. This theory assumes —
1. That the ultimate particles of all magnetizable bodies
have closed electric circuits in which electric currents are con-
tinually flowing.
2. That in an unmagnetized body these circuits neutralize
one another, because they have different directions.
3. That the act of magnetization consists in such a polariza-
tion of the particles as will cause these currents to flow in
12 ELECTRO-DEPOSITION OF METALS.
one and the same direction, magnetic saturation being reached
when all the separate circuits are parallel to one another.
4. That coercive force is due to the resistance these circuits
offer to a change in the direction of their planes.
Guided by these considerations, Ampere produced a coil of
wire, called a solenoid, which is the equivalent of the magnetiz-
ing circuit assumed by his theory. It therefore follows that an
electric current sent through a coil of insulated wire surround-
ing a rod or bar of soft iron, or other readily magnetizable ma-
terial, will make the same a magnet. A magnet so produced
is called an electro-magnet; the magnetizing coil is called a
helix, or solenoid. The polarity of the magnet depends on the
direction of the current, or on the direction of winding of the
helix or solenoid. The improbability of an electric current
continually flowing in a circuit without the expenditure of en-
ergy, has led many scientific men to reject Ampere's theory of
magnetism.
If an iron or steel needle be suspended free in the neighbor-
hood of a magnet, it assumes a determined direction according
to its greater or smaller distance from the poles or from the
neutral zone ; however, before the needle assumes this direction
it swings quickly with a shorter stroke, or slowly with a longer
stroke, according to the greater or smaller attractive force ex-
erted upon it. The space within which the magnetic action of
a magnet is exercised is called the magnetic field, and the mag-
netic as well as the electric attractions and repulsions are, ac-
according to Coulomb, as the densities of the fluids acting upon
each other and inversely as the square of their distance.
2. ELECTRICITY.
In an ordinary state solid bodies exhibit no attractive effect
upon small light particles, such as strips of paper, balls of elder-
pith, etc ; but by rubbing many solid bodies with a piece of dry
cloth or fur they acquire the property of attracting such light
bodies as mentioned above. The cause of this phenomenon is
called electricity, and the bodies which possess this property of
MAGNETISM AND ELECTRICITY. 13
becoming electric by friction are termed idio-electrics, and those
which do not appear to possess it, non- electrics. Gray, in 1727,
found that all non-electric bodies conduct electricity, and hence
are conductors, while those which become electric by friction
are non-conductors of electricity. Strictly speaking, there are
no non-conductors, because the resins, silk, glass, etc., conduct
electricity, though only very slightly. It is therefore better to
distinguish good and bad conductors. To test whether a body
belongs to the idio-electrics, the so-called electroscope is used,
which in its simplest form consists of a glass rod mounted on a
stand, and bent at the top into a hook, from which hangs by a
silken thread or hair a pith ball. If, on bringing the rubbed
body near the pith ball, the latter is attracted, the body is elec-
tric ; whilst if the ball is not attracted, the body is either non-
electric or its electricity is too slight to produce an attractive
effect.
From the following experiments it was found that there exist
two kinds of electricity: When a rubbed rod of glass or shellac
is brought near the ball of elder-pith suspended to a silk thread,
the ball is attracted, touches the rod, adheres for a few moments
and is then repulsed. This repulsion is due to the fact that the
ball by coming in contact with the rod becomes itself electric,
and its electricity must first be withdrawn by touching with the
hand before it can again be attracted by the rod. By now
taking two such balls, one of which has been made electric by
touching with a glass rod, which had been rubbed with silk,
and the other by touching with a shellac rod rubbed with cloth,
it will be observed that the ball, which is repulsed by the glass
rod, is attracted by the shellac rod, and vice versa. These two
kinds of electricity are called vitreous or positive, and resinous
or negative electricity, and it has been found that electricities of
a similar name attract, and electricities of an opposite name re-
pel, each other.
For want of a concrete knowledge of the electric agent which
produces the electric phenomena, various theories or hypotheses
have been advanced to explain these phenomena and the action
14 ELECTRO-DEPOSITION OF METALS.
of the electric forces. Only two of the best known theories or
hypotheses, shall here be mentioned.
Double fluid hypothesis of electricity. By this hypothesis it
is endeavored to explain the causes of electric phenomena by
the assumption of the existence of two different electric fluids.
The double fluid hypothesis assumes: —
1. That the phenomena of electricity are due to two tenuous
and imponderable fluids, the positive and the negative.
2. That the particles of the positive fluid repel one another,
as do also the particles of the negative fluid ; but that the par-
ticles of the positive fluid attract the particles of the negative,
and vice versa.
3. That the two fluids are strongly attracted by matter, and
when present in it produce electrification.
4. That the two fluids attract one another and unite, thus
masking the properties of each.
5. That the act of friction separates these fluids, one going
to the rubber and the other to the thing rubbed.
Single fluid hypothesis of electricity. By this hypothesis it is
endeavored to explain the cause of electric phenomena by the
assumption of the existence of a single electric fluid.
The single fluid hypothesis assumes: —
1. That the phenomena of electricity are due to the presence
of a single, tenuous, imponderable fluid.
2. That the particles of this fluid mutually repel one another,
but are attracted by all matter.
3. That every substance possesses a definite capacity for
holding the assumed electric fluid, and that when this capacity
is just satisfied, no effects of electrification are manifest.
4. That when the body has less than this quantity present, it
becomes negatively excited, and when it has more, positively
excited.
5. That the act of friction causes a redistribution of the fluid,
part of it going to one of the bodies, giving it a surplus, thus
positively electrifying it, and leaving the other with a deficit,
thus negatively electrifying it.
MAGNETISM AND ELECTRICITY. 15
However, the epoch-making investigations of Prof. Herz, of
Bonn (1889), have led to different views regarding the nature
of electricity. Herz has shown by experiments that electricity
is transmitted in space by waves like heat and light, and he has
determined the length and velocity of electrical waves. From
this it has been ascertained that electricity is founded upon
motion, and that the current appearing in a conductor has to
be referred to vibrations of the molecules forming the conduc-
tor, relatively to vibrations of the ether enveloping the mole-
cules. By the term ether is designated the imponderable
medium pervading all space. Hence electricity is an energy,
just the same as light and heat are manifestations of energy.
According to Coulomb, the electric attractions and repulsions
are as the densities of the fluids acting upon each other, and in-
versely as the square of the distance.
However, a current of electricity is created not only by fric-
tion, but also by the contact of various metals. In the same
manner as the copper and iron in Galvani's experiments with
the frog -leg, other metals and conductors of electricity also be-
come electric by contact, the electric charges being, however,
stronger or weaker, according to the nature of the metals. If
zinc be brought in contact with platinum, it becomes more
strongly positively electric than when in contact with copper ;
whilst, however, copper in contact with zinc is negatively ex-
cited, in contact with platinum it becomes positively electric.
By now arranging the metals in a series, so that each preceding
metal becomes positively electric in contact with the succeed-
ing one, a series of electro-motive force or tension is obtained, in
which the metals or conductors of electricity sland as follows :
+ Zinc, cadium, tin, iron, lead, copper, nickel,
Silver, antimony, gold, platinum, carbon — .
While two metals of the series of electro-motive force or tension
touching each other become electrically excited in such a manner
that one becomes positively and the other negatively electric, an
exchange of the opposite electricities takes place by introducing
1 6 ELECTRO-DEPOSITION OF METALS.
a conducting fluid between the metals. Thus, if a plate of zinc
and a plate of copper connected by a metallic wire are immersed
in a conducting fluid, for instance, dilute sulphuric acid, the
electricity of the positive zinc passes through the fluid to the
negative copper, and returns through the wire — the closing cir-
cuit— to the zinc. However, in the same degree with which the
electricities equalize themselves, new quantities of them are
constantly formed on the points of contact of the metals with
the conducting fluid ; and, hence, the flow of electricity is con-
tinuous. This electric current generated by the contact of
metals and fluids is called the galvanic current', or, since it is
generated by the intervention of fluid conductors, hydro- electric
current. A combination of conductors which yields such a
galvanic current, is called a galvanic element or galvanic chain.
It would here be the place to discuss the various galvanic
elements, but it is thought better to describe them in a separate
chapter, and first to explain the laws and the actions of the gal-
vanic current.
Electrical potential. — The property of electricity correspond-
ing to head or pressure, as applied in speaking of gas or water-
power, is termed the electrical potential. Two bodies have the
same electrical potential when, connected by a metallic wire,
they develop no electricity.
Electro-motive force. — If, however, two bodies connected by a
metallic wire possess unequal electrical potentials, a movement
of the electricity takes place, and the force which produces this
movement or current is called the electro- motive force or ten-
sion. It, therefore, corresponds to the difference of the poten-
tials ; and the magnitude of this difference of the potentials is
the measure for the electro-motive force.
Resistance. — All conductors offer a certain amount of resist-
ance to the forward movement of the electric current. By con-
necting, for instance, two bodies charged with electricity and
possessing a difference of potentials, by a metallic conductor, a
certain time is required for the compensation of the difference
of potentials, or, in other words, before the electrical equilibrium
MAGNETISM AND ELECTRICITY. I/
is established. By now keeping the difference of potentials
constant, the quantity of electricity which passes through the
closing conductor — the closing circuit — depends on the resist-
ance which the latter offers to the passage of the current.
The resistance of a conductor is proportional to its length and
inversely to its cross-section and its conducting capacity ; i. e., the
longer the conducting circuit the greater the resistance, and the
greater its cross-sections the smaller the resistance. Wires of
small diameter will, therefore, offer greater resistance to the
current than those with larger diameter, and wires with good
conducting capacity will produce less resistance than those with
poor conducting capacity. According to Lazere Weiler, the
conductivity of metals is as follows: —
Name of Metal.
Mean
Conductivity.-
Alloys, etc.
Mean
Conductivity.
Si
7C O
Cu "12 "
Si
75-°
Gold
80 6
p
•7
C C I
y
Cu " 10 "
Pb,
100
Cu 10 "
Al.
126
16.7
Cu 10 "
As,
Q.I
. 1
16 d.
Cu 20 "
Sn
8 A
Tin
Zn
211
Lead
8*8
^u OD
86 6
Nickel
A^'
16 i
Antimony >
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 = ney 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.
24
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 TV 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 O°C. The ohm is equal to io9 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 io8 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 io9 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 tofconstitute 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 y2 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- 5200 = °-29 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.
69
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 M1 (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 Bf. 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 y2 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- FIG. 51-
sition that the needle in the north position,
which it occupies, points to o° wrhen 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
96
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
98
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 Rv
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 Rl ; the screw marked " weak " of the resist-
ance board R1 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 R2, 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 R3 and R4 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. NN1 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
D£S/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.
I24
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 42
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.
I58
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 ^y2 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 yt 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-
strings—might 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 dy 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 Per 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-
ingconsists 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 TV 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 \y2 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, il/&
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 \y2
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 : IQ8 = 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 at 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. jn 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 yT 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-S2 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, and 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 y2 pint of water, and the potas-
sium cyanide in I y2 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 KK1 to the friction-pulley Ft 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, PtCl4. 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 Ty 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 \y2 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 anodesT 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 uLa 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 I3OO°F. 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 TV 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
352 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 y2 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
.I76
5 per cent.
ii
13 "
17 "
18 "
19
20
21
23
24
25
10°
12°
I cO
16° ..
17° •
18° :::::::::::::::.:::
IQo .
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 y2
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 24-9 = 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
398 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, \y2 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 y2 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 y2 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 Part =
= 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
442 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- I39-
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
32
—
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
I30
I.OOO
o° or 10
0°
1.700
—
I40
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
78
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
—
J9-5°
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
31
197.4
39-1
104.4
854
1044
794
28
108
23
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.50
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
^•D1 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
Lea(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-uy/.)
Tin
Sn
1UO
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 y1^ 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,
y2 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
-<L> 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
0 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
0-5555
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
IS-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 Per 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
•25
•31
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°
60.8C
64.4°
68°
75.2°
82.4C
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 !-I07
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.
At3^4
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.
&«o«5
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.
<u
a
3
<J
d
N
.S
-d
5
TJ
-3
£
Bismuth.
Antimony.
Arsenic.
|
PARTS.
Armenian elastic
574
70
66
60
75
4
10
80
78
42
21
100
100
90
93
84
84
82
80
5°
53
4
55
11.9
ICO
86.6
IOO
80
76
88
84
25
30
32
40
25
6
ii
10.5
3-5
31-25
3-5
i
J7
24.9
12
12.6
20
24
12
16
7°-5
22
20
22
58
25
2O
25
10
16
4
18
8
4
3
2
2
1.2
2.4
50
2
4
5
3
O.2
1.2
13
i —
25-5
62
—
9
Brass for articles worked with the
" for sheet
Britannia •
<(
" for clocks
" for medals
" for large ordnance
" for small ordnance
—
—
—
—
—
« «
« «
4
'5-75
3
23
8
8
5
—
i
3
Darcet's fusible alloy
« « «
«( « «
« «
«« «
« «
Potin (French yellow brass) ....
Talmi gold
Telescope mirrors (reflectors)
Tombac
« pale
« red
* For a full description of alloys and amalgams see "The Metallic Alloys," edited
by W. T. Brannt. Philadelphia. Henry Carey Baird & Co. 1896.
468
APPENDIX.
2. Solders.
a. Soft Solder.
Tin.
Lead.
Tin.
Lead.
Melts
Melts
PARTS.
at degrees F.
PARTS.
at degrees F.
25
558°
l&
334°
10
541
2
340
5
5"
3
356
3
482
4
2
441
5
378
I
37°
6
38i
b. Hard Solder.
Brass.
Zinc.
Tin.
PARTS.
gc 42
12 ?8
« «
_
((
j
2
u
Half white
12
/Id.
2O
2
"White
4O
2
g
u
22
2
«
18
12
78 2S
17 2C
ou
•/••3
c. Silver Solder.
Silver.
Copper.
Brass.
Tin.
Zinc.
PARTS.
A.O
JO
AQ
AQ
10
•72
J"
20
32
Silver solder for steel
3
*
APPENDIX,
d. Gold Solder.
469
Gold.
Silver.
Copper. I Zinc.
PARTS.
9
12
3
2
I
I
I
11.94
10
2
7
2
o-5
2
2
54-74
5
I
3
i
0-5
2
28.17
5.01
I
Soft « " " 750
" « « ,-g,.
" " " less than 583
« « a <t « «
Solder readily fusible «
« « ' « for yellow gold
of the melting-points of some metals.
Metals.
Degrees
Fahrenheit.
Metals.
Degrees
Fahrenheit.
Tin
86
Gold
2372
Lead ....
CO
Zinc
773 6
Nickel
2912
Antimony
809 6
Steel . . .
3OQ2 to 3AC2
Brass
rgCQ
IOOA
3452 o 3 12
of high temperatures.
Description.
Degrees
Fahrenheit.
Description.
Degrees
Fahrenheit.
Incipient red heat «... . .
977
A red heat
77
080
1877
A dull red heat visible in
10/j
1006
IOOO
-jOOO
Heat of a common fire ....
1140
I2OO
Heat of a good blast
33OO
Dull red heat
I7IO
oov-"-<
specific gravity and content of solutions of potassium
carbonate at 57.2° Fahrenheit, according to Gerlach.
Potassium
carbonate,
per cent.
Specific gravity.
Potassium
carbonate,
per cent.
Specific gravity.
Potassium
carbonate,
per cent.
Specific gravity.
2
1.01829
20
I.I9286
38
1.39476
4
1.03658
22
I.2I402
40
1.41870
6
i^>5513
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
S03.
H2S04.
SO3.
H2S04.
S03.
H2SO4.
SO3.
H2S04.
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
56-9
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
56
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
25-3
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
31
.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
™-
HN03.
N2O5.
HN03. N20S.
F
HN03.
N20S.
HN03.
N205.
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
1.052
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
I5-1
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
ll
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
27.8
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
—
—
25
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
S1-0} -549
97-3
83.4
—
—
27
I.23I
34-6
29.7
37-Q
31.7
5J-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
25
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
25
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
J3-5
ii
0.000739 1352.5
31
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.
0°
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
25
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
J3
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
0
.307
.32495
.340
.324
••34
i
.283
.2893
•3
•3
•3
2
.263
.25763
.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
.083
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
25
.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
•OI55
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
I7-25
17.48
20.838
19.688
oooT
.40964
444.68 448-88
5°7-95
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
I77-55
200.91
189.82
9.6611
9.7899
11.671
11.027
3
.22942
13948
140.80
I59-32
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
43-751
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 3J-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
J7
•045257
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-53I5
.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
•95051
.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
27 •
.014195
0.5340
0-5391
.6099
0.5763
.53231
•53941
•64303
•60755
28
.012641
0.4235
0-4275
.4837
0.4570
•474°4
.48036
•57264
•54103
29
.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
•2543i
.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
Barb£dienne 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
484
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.cmann 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 wayt
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, 0
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,
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10 HENRY CAREY BAIRD & CO.'S CATALOGUE.
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DAVIS. — The Manufacture of Leather:
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DE GRAFF. — The Geometrical Stair-Builders' Guide :
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HENRY CAREY BAIRD & CO.'S CATALOGUE. n
DE KONINCK— DIETZ.— A Practical Manual of Chemical
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A.S applied to the Manufacture of Iron from its Ores, and to Cast Iron,
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DJNCAN.— Practical Surveyor's Guide:
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DUPLAIS. — A Treatise on the Manufacture and Distillation
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DUSSAUCE.— Practical Treatise on the Fabrication of Matches,
Gun Cotton, and Fulminating Powder.
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DYER AND COLOR-MAKER'S COMPANION:
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EDWARDS. — Modern American Locomotive Engines,
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12 HENRY CAREY BAIRD & CO.'S CATALOGUE.
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EDWARDS.— The Practical Steam Engineer's Guide
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EISSLER.— The Metallurgy of Gold :
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and the Assaying, Melting, and Refining of Gold. By M. EISSLER.
With 132 Illustrations. I2mo. ..... $5.00
EISSLER.— The Metallurgy of Silver :
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FAIRBAIRN.— The Principles of Mechanism and Machinery
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GRUNER.— Studies of Blast Furnace Phenomena:
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HASERICK.— The Secrets of the Art of Dyeing Wool, Cotton,
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HOFFER. — A Practical Treatise on Caoutchouc and Gulta
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HULME. — Worked Examination Questions in Plane Geomet-
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KEENE. — A Hand-Book of Practical Gauging:
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KEMLO.— Watch-Repairer's Hand-Book :
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i6 HENRY CAREY BAIRD & CO.'S CATALOGUE.
KENTISH.— A Treatise on a Box of Instruments,
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I ERL.— The Assayer's Manual:
An Abridged Treatise on the Docimastic Examination of Ores, and
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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
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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-
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Comprising Electro-Plating and Gnlvanoplastic Operations, the De-
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ing of Metals, the Methods of Grinding and Polishing, as well as
Descriptions of the Electric Elemenis, Dynamo-Electric Machines,
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with additions by WM. T. BRANNT. Third Edition, thoroughly re-
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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-
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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
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Comprising Practical Mechanics, with Rules and Calculations applied
to Spinning; Sorting, Cleaning, and Scouring Wools; the English
and French Methods of Combing, Drawing, and Spinning Worsteds,
and Manufacturing Carded Yarns. Translated from the French of
CHARLES LEROUX, Mechanical Engineer and Superintendent of a
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Chemist and Engineer. Illustrated by twelve large Plates. To which
is added an Appendix, containing Extracts from the Reports of the
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:
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Sixtieth thousand. Thoroughly revised, with the addition of New
Receipts. I2mo. . $1.50
LE VAN. — The Steam Engine and the Indicator :
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BARNET LE VAN. Illustrated by 205 Engravings, chiefly of Indi-
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LIEBER. — Assayer's Guide :
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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
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HENRY CAREY BAIRD & CO.'S CATALOGUE
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LUKIN.— The Young Mechanic t
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I2mo. . . . . . . . . . . $i-75
MAIN and BROWN. — Questions on Subjects Connected with
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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
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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
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MAKINS.— A Manual of Metallurgy:
By GEORGE HOGARTH MAKINS. 100 engravings. Second edition
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MARTIN. — Screw-Cutting Tables, for the Use of Mechanica)
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Showing the Proper Arrangement of Wheels for Cutting the Threads
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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
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By GUILFORD L. MOLESWORTH, Member of the Institution of Civil
Engineers, Chief Resident Engineer of the Ceylon Railway. Full-
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MOORE.— The Universal Assistant and the Complete Me-
chanic :
Containing over one million Industrial Facts, Calculations, Receipts^
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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-
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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-
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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
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NEVILLE.— Hydraulic Tables, Coefficients, and Formulae, foi
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Weirs, Pipes, and Rivers :
Third Edition, with Additions, consisting of New Formulae for the
Discharge from Tidal and Flood Sluices and Siphons; general infor-
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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«
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NICHOLSON.— A Manual of the Art of Bookbinding :
Containing full instructions in the different Branches of Forwarding,
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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
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NORM ANDY.— The Commercial Handbook of Chemical An-
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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-
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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,
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etc., etc. By FREDERICK OVERMAN, M. E. A new Edition, to
which is added a Supplement on Statuary and Ornamental Moulding,
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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
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PROCTOR. — A Pocket-Book of Useful Tables and Formulas
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REGNAULT. — Elements of Chemistry:
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HENRY CAREY BAIRD & CO.'S CATALOGUE. 23
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24 HENRY CAREY BAIRD & CO.'S CATALOGUE.
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WAHNSCHAFFE.— A Guide to the Scientific Examination
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WARNER. — New Theorems, Tables, and Diagrams, for the*
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WATSON.— A Manual of the Hand-Lathe :
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WATSON. — The Modern Practice of American Machinists and
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HENRY CAREY BAIRD & CO.'S CATALOGUE. 29
\vith Workshop Management, Economy of Manufacture, the Steam
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WATT.— The Art of Soap Making :
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WEATHERLY. — Treatise on the Art of Boiling Sugar, Crys-
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"WILSON. — First Principles of Political Economy:
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'WOODS. — Compound Locomotives:
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30 HENRY CAREY BAIRD & CO.'S CATALOGUE.
WOHLER.— A Hand-Bookof Mineral Analysis:
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WORSSAM.— On Mechanical Saws:
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RECENT ADDITIONS.
BRANNT. — Varnishes, Lacquers, Printing Inks and Sealing -
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BRANNT — The Practical Scourer and Garment Dyer:
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203 pages. I2mo. .,.....' $2.00
BRANNT.— Petroleum .
Its History, Origin, Occurrence, Production, Physical and Chemical
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German of Prof. Hans Hoefer and Dr. Alexander Veith, by WM.
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BRANNT. — A Practical Treatise on the Manufacture of Vine-
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BRANNT.— The Metal Worker's Handy-Book of Receipts
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DEITE. — A Practical Treatise on the Manufacture cf Per*
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EDWARDS. — American Marine Engineer, Theoretical and
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EDWARDS. — 900 Examination Questions and Answers:
For Engineers and Firemen (Land and Marine) who desire to ob-
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POSSELT.— Technology of Textile Design :
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POSSELT. — The Jacquard Machine Analysed and Explained:
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POSSELT. With 230 illustrations and numerous diagrams. 127 pp.
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POSSELT. — The Structure of Fibres, Yarns and Fabrics:
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Growth and Manipulation of Cotton, Wool, Worsted, Silk. Flax,
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