ELECTRO-DEPOSITION! WORKS ZY THE SAME AUTHOR. ELECTRO -METALLURGY Practically Treated. Ninth Edition, Revised, with Additional Matter and Illustrations, including the most Recent Processes. By ALEXANDER WATT. 4s. cloth boards. " From this book both amateur and artisan may learn everything neces- sary for the successful prosecution of electro-plating." Iron. "A practical treatise for the use of those who desire to work in the art of electro-deposition as a business." English Mechanic. THE ART OF SOAP-MAKING : a Practical Handbook of the Manufacture of Hard and Soft Soaps, Toilet Soaps, &c. Including 1 many New Processes, and a Chapter on the Recovery of Glycerine from Waste Leys. By ALEXANDER WATT. With numerous Illustrations. Fourth Edition, carefully Revised and Enlarged. Crown Svo, 7s. 6d. cloth. " The work will prove very useful, not merely to the technological stu- dent, but to the practical soapboiler who wishes to understand the theory of his art." Chemical News. " Mr. Watt's book is a thoroughly practical treatise on an art which has almost no literature in our language. Nature. THE ART OF LEATHER MANUFACTURE; Being a Practical Handbook, in which the operations of Tanning, Currying, and Leather Dressing are fully described, the Principles of Tunning explained, and many Recent Processes Introduced ; as also Methods for the Estimation of Tannin, and a Description of the Arts of Glue Boiling, Gut Dressing, &c. By ALEXANDER WATT. With numerous Illustrations. Third Edition, crown Svo, 9s. cloth. "Every item of use and interest to the leather trade has been touched upon, and the descriptions and explanations of the various processes are exhaustively given." Tanners' and Curriers' Journal. "A most lucid and readable book upon difficult and intricate subjects. Every known process of tanning, from the most primitive to the most recent, is fully and accurately described." Scottish Leather Trader. THE ART OF PAPER MAKING : A Practical Handbook of the Manufacture of Paper from Rags, Esparto, Straw, and other Fibrous Materials, Including the Manufacture of Pulp from Wood Fibre, with a Description of the Machinery and Appliances used. To which are added Details of Processes for Recovering Soda from Waste Liquors. By ALEXANDER WATT. With Illustrations. Crown Svo, 7s. 6d. cloth. "This book is succinct, lucid, thoroughly practical, and includes every- thing of interest to the modem paper maker. It is the latest, most practi- cal, and most complete work on the paper-making art before the British public." Paper Record. CROSBY LOCKWOOD & SON, 7, STATIONEES' HALL COUBT, LONDON, E.G. IVTETALLO CHROMES (r fin*? 358). ELECTRO-DEPOSITION A PRACTICAL TREATISE ON THE ELECTROLYSIS OF GOLD, SILVER, COPPER, NICKEL, AND OTHER METALS, AND ALLOYS WITH DESCRIPTIONS OF VOLTAIC BATTERIES, MAGNETO AND DYNAMO-ELECTRIC MACHINES, THERMOPILES, AND OF THE MATERIALS AND PROCESSES USED IN EVERY DEPARTMENT OF THE ART AND SEVERAL CHAPTERS ON ELECTRO-METALLURGY BY ALEXANDER WATT. AUTHOR OF " ELECTRO-METALLURGY " i&& ART OF SOAP- MAKING," "THE ART OF ," ETC. ttcrxrtts v THIRD EDITION^EVISED, CORRECTED, AND ENLARGED LONDON CROSBY LOCKWOOD AND SON 7, STATIONERS' HALL COURT, LUDGATE HILL 1889 \All rights reserved'] , v LONDON : jY'' JC S. VIRTUE AND CO., LIMITED, , CITY ROAD. PREFACE. IN contemplating the present work, the Author's desire was to furnish those who are engaged in the ELECTRO- DEPOSITION OF METALS, and in the equally important department of Applied Science ELECTRO-METALLURGY, with a comprehensive treatise, embodying all the practical processes and improvements which the progress of Science has, up to the present time, placed at our command. While the long-continued success of the Author's former work upon this subject, "Electro-Metallurgy Practically Treated " now passing through its Eighth Edition testi- fies to its having filled a useful place in technical literature, the art of which it treats has during recent years attained such a high degree of development, that it was felt that a more extended and complete work was needed to represent the present advanced state of this important industry. In carrying out this project, the Author's aim has been to treat the more scientific portion of the work in such a manner that those who are not deeply learned in Science may readily comprehend the chemical and electrical prin- ciples of Electrolysis, the knowledge of which is essential to those who would practise the art of Electro-Deposition with economy and success. He has also endeavoured to render the work thoroughly practical in character in all its most 838309 VI PREFACE. important details ; and having himself worked most of the operations of the art upon a very extensive scale, he is enabled in many instances to give the results of his own practical experience. ELECTRO-METALLURGY, which is now recognised as a distinct branch of electro-chemistry, has been treated sepa- rately, and those processes which have been practically adopted, such as the electrolytic refining of crude copper} are, exhaustively given, while other processes, now only upon their trial, are described. In this section ai^o will be found a description of the new process of electric smelting, as ap- plied, more especially, to the production of aluminium and silicon bronzes. In conclusion, the author tenders his best thanks to those who kindly furnished him with information, for the readiness and promptitude with which they complied with his requests. LONDON, December, 1885. PEEFACE TO THE THIRD EDITION. IN producing a new and revised Edition of this work, the Author has been enabled to make some further additions, in the form of an Appendix, which it is hoped will be found interesting and useful He has also eliminated certain details from the body of the work which later experience has shown to be of a doubtful character, and substituted other matter which he trusts will be more useful to his readers. LONDON, November, 18S8. CONTENTS. CHAPTER I. HISTORICAL REVIEW OF VOLTAIC ELECTRICITY. Galvani's Discovery. Volta's Discovery. Simple Voltaic Circle. The Voltaic Pile. Cruickshank's Trough Battery. Dr. Babbington's Battery. Volta's Couronne des Tasses. Dr. Wollaston's Battery. Daniell's Batteiy. Smee's Battery. Grove's Battery. Compound Grove Battery. Callan's Iron Batten-. Bunsen's Battery. "Walker's Graphite Battery. Leclanche's Battery. Bichromate Battery. Marie-Davy Battery. Secondary Batteries, or Accumu- lators i CHAPTER II. ELECTRO-MAGNETISM. MAGNETO-ELECTRICITY.-* DYNAMO -ELECTRICITY. Oersted's Discovery. Electro-magnetism. The Galvanometer. Elec- tro-magnets. Magneto-electricity. Saxton's Magneto-electric Ma- chine. Woolrich's Magneto-electric Machine. Wilde's Magneto- electric Machine. Gramme's Magneto-electric Machine. Dynamo- electricity. Siemens' Dynamo-electric Machine Weston's Dynaino- electric Machine. Giilcher's Dynamo-electric Machines. Cromp- ton's Dynamo-electric Machine. Schuckert's Dynamo-electric Machine. Mather's Dynamo-electric Machine . . . .18 CHAPTER III. THERMO-ELECTRICITY. Seebeck's Discovery of Thermo-Electricity. Thermo-electric Laws. Thermo-electric Piles and Batteries. C. Watt's Thermo-electric Battery. BecquerePs Thermo-Pile. Clamond's Thermo-electric Pile. Wray's Thermo-Pile. Noe's Thermo-Battery. The Future of Thermo-Electricity 39 Vlll CONTENTS. CHAPTER IY. HISTORICAL REVIEW OF ELECTRO -DEPOSITION. PAGE Announcement of Jacobi's Discovery. Jordan's Process Published. Jordan's Process. Spencer's Paper on the Electrotype Process. Effect of Spencer's Paper. Vindication of Jordan's Claim. Mr. Dircks on Jordan's Discovery. Sir Henry Bessemer's Experiments. Dr. Golding Bird's Experiments. Origin of the Porous Cell . ^i CHAPTER V. THEORY OF ELECTROLYSIS. Chemical Powers of the Voltaic Pile. Faraday's Nomenclature of Electro-chemical Action. Direction of the Current. Decomposition of Water. Action of the Electric Current upon Compound Sub- stances. Electrolysis of Sulphate of Copper. Electrolysis of Sul- phate of Potash, fec. Electrical Transfer of Elements. Practical Illustrations of the Electrolytic Theory 70 CHAPTER VI. ELECTRICAL THEORIES IN THEIR RELATION TO THE DEPOSITION OF METALS. Conductors and Insulators. Relative Conducting Powers of Metals. Definition of Electrical Terms. Simple and Compound Voltaic Circles. Resistance : Ohm's Law. Application of Ohm's Law to Compound Voltaic Circles. Electrical Units. Electromotive Force of Batteries. Electrolytic Classification of Elements . . .80 CHAPTER VII. ELECTRO-DEPOSITION OF COPPER. Electrotyping by Single-cell Process. Copying Coins and Medals. Moulding Materials. Gutta-percha. Plastic Gutta-percha. Gutta-percha and Marine Glue. Beeswax. Sealing-wax. Stear- ine. Stearic Acid. Fusible Metal. Elastic Moulding Material- Plaster of Paris 91 CHAPTER VIII. ELECTRO -DEPOSITION OF COPPER (continued}. Moulding in Gutta-percha. Plumbagoing the Mould. Treatment of the Electrotype. Bronzing the Electrotype. Moulds of Sealing- wax. Copying Plaster of Paris Medallions. Preparing the Mould. Plumbagoing. Clearing the Mould. -Wax Moulds from Plaster Medallions. Moulds from Fusible Metal 99 C )NTENTS. IX CHAPTER IX. ELECTRO-DEPOSITION OF COPPER (continued}. PAGE Electrotyping by Separate Battery. Arrangement of the Battery. Copying Plaster Busts. Guiding Wires. Moulding in Plaster of Paris. Copying Animal Substances. Electro-coppering Flowers, Insects, &c. Copying Vegetable Substances. Depositing Copper upon Glass, Porcelain, &c. Coppering Cloth no CHAPTER X. ELECTRO-DEPOSITION OF COPPER (continued). Electrotyping Printers' Set-up Type. Plumbagoing the Forme. Preparation of the Mould. Filling the Case. Taking the Impres- sion. The Cloth. Removing the Forme. Building. Plumbago- ing the Mould. Knight's Plumbagoing Process. Wiring. Hoe's Electric Connection Gripper. Metallising the Moulds. Adams' Process of Metallising Moulds. Quicking. The Depositing Bath. Batteries. Treatment of the Electrotype. Finishing. Electro- typing Wood Engravings, &c. Tin Powder for Electrotyping . 122 CHAPTER XI. ELECTRO-DEPOSITION OF COPPER (continued). Deposition of Copper by Dynamo-electricity. Copying Statues, &c. Lenoir's Process. Deposition of Copper on Iron. Coppering Printing Rollers. Schlumberger's Process. Producing Printing Rollers by Electricity. Coppering Cast Iron. Coppering Steel Wire for Telegraphic Purposes. Coppering Solutions. Dr Eisner's Solu- tion. Walenn's Process. Gulensohn's Process. Weil's Copper- ing Process. Electro-etching. Glyphography. Making Copper Moulds by Electrolysis. Making Electrotype Plates from Drawings Coppering Steel Shot. Coppering Notes 139 CHAPTER XII. DEPOSITION OF GOLD BY SIMPLE IMMERSION. Preparation of Chloride of Gold. Water Gilding. Gilding by Immer- sion in a Solution of Chloride of Gold. Gilding by Immersion in an Ethereal Solution of Gold. Solution for Gilding Brass and Copper. Solution for Gilding Silver. Solution for Gilding Bronze. French Gilding for Cheap Jewellery. Colouring Gilt Work. Gilding Silver by Dipping, or Simple Immersion. Pre- paration of the Work for Gilding. Gilding by Contact with Zinc, Steele's Process. Gilding with the Rag 157 X CONTENTS. CHAPTER XIII. ELECTRO-DEPOSITION OF GOLD. PAQB Gilding by Direct Current, or Electro-Gilding. Preparation of Gilding Solu tions. Gilding Solutions (Becquerel's. Fizeau's. Wood's. M. de Briant's). French Gilding Solutions. Gilding Solutions made by the Battery Process (De Ruolz's). Cold Electro-Gilding Solutions. Observations on Gilding in Cold Baths. Ferrocyanide Gilding Solution. Watt's Gilding Solution. Record's Gilding Bath 165 CHAPTER XIV. ELECTRO -DEPOSITION OF GOLD (continued). General Manipulations of Electro-gilding. Preparation of the Work. Dead Gilding. Causes which affect the Colour of the Deposit. Gilding Gold Articles. Gilding Insides of Vessels. Gilding Silver Filigree Work. Gilding Army Accoutrement Work. Gilding German Silver. Gilding Steel. Gilding Watch Movements . . 177 CHAPTER XV. VARIOUS GILDING OPERATIONS. Electro-gilding Zinc Articles. Gilding Metals with Gold Leaf. Cold Gilding. Gilding Silk, Cotton, &o. Pyro-gilding. Colour of Electro-deposited Gold. Gilding in various Colours. Colouring Processes. Re-colouring Gold Articles. Wet-Colour Process. French Wet-Colouring. London Process of Wet-Colouring . .192 CHAPTER XVI. MERCURY GILDING. Preparation of the Amalgam The Mercurial Solution. Applying the Amalgam. Evaporation of the Mercury. Colouring. Bright and Dead Gilding in Parts. Gilding Bronzes with Amalgam. Ormoulu Colour. Red-Gold Colour. Ormoulu. Red Ormoulu. Yellow Ormoulu. Dead Ormoulu. Gilder's Wax. Notes on Gilding CONTENTS. XI CHAPTER XVII. ELECTRO -DEPOSITION OF SILVER. PAGE Preparation of Nitrate of Silver. Observations on Commercial Cyan- ide. Preparation of Silver Solutions. Bright Plating. Deposi- tion by Simple Immersion. Whitening Articles by Simple Immersion. Whitening Brass Clock Dials, &c 219 CHAPTER XVIII. ELECTRO-DEPOSITION OF SILVER (continued). Preparation of New Work for the Bath. Quicking Solutions, or Mercury Dips. Potash Bath. Acid Dips. Dipping. Spoon and Fork Work. Wiring the Work. Arrangement of the Plating Bath. Plating Battery. Motion given to Articles while in the Bath. Cruet Stands, &c. Tea and Coffee Services. Scratch-brushing . 233 CHAPTER XIX. ELECTRO -DEPOSITION OF SILVER (continued). Plating Britannia Metal, &c. Plating Zinc, Iron, &c. Eeplating Old Work. Preparation of Old Plated Ware. Stripping Silver from Old Plated Articles. Stripping Gold from Old Plated Articles. Hand Polishing. Resilvering Electro-plate. Characteristics of Electro-plate. Depositing Silver by Weight. Roseleur's Argyro- metric Scale. Solid Silver Deposits. On the Thickness of Electro-deposited Silver. Pyro-plating. Whitening Electro-plated Articles. Whitening Silver Work 250 CHAPTER XX. IMITATION ANTIQUE SILVER. Oxidised Silver. Oxidising Silver. Oxidising with Solution of Platinum. Oxidising with Sulphide of Potassium. Oxidising with the Paste. Part-gilding and Oxidising. Dr. Eisner's Process. Satin Finish. Sulphuring Silver. Niello, or Nielled Silver. Pink Tint upon Silver. Silvering Notes , 269 CHAPTER XXI. ELECTRO-DEPOSITION OF NICKEL. Application of Nickel-plating. The Depositing Tank. Conducting Rods. Preparation of the Nickel Solution. Nickel Anodes. Nickel-plating by Battery. The Twin-Carbon Battery. Observa- tions on Preparing Work for Nickel-plating. The Potash Bath. Dips, or Steeps. Dipping Acid. Pickling Bath 280 Xll CONTENTS. CHAPTER XXII, ELECTRO-DEPOSITION OF NICKEL (continued). PACK Preparation of Nickeling Solutions. Adams' Process. Unwin's Pro- cess. Weston's Process. Powell's Process. Potts' Process. Double Cyanide of Nickel and Potassium Solution. Solution for Nickeling Tin, Britannia Metal, &c. Simple Method of Preparing Nickel Salts. Desmur's Solution for Nickeling Small Articles. . 291 CHAPTER XXIII. ELECTRO -DEPOSITION OF NICKEL (continued}. Preparation of the Work for Nickel- plating. The Scouring Tray. Brass and Copper Work. Nickeling small Steel Articles. Nickel- ing small Brass and Copper Articles. Nickeling by Dynamo- electricity. Nickeling Mullers, Sausage Warmers, &c. Nickeling Bar Fittings, Sanitary Work, &c. Nickeling Long Pieces of Work. Dead Work. Nickeling Stove Fronts, &c. Nickeling Bicycles, &c. Nickeling second-hand Bicycles, &c. Nickeling Sword- scabbards, &c. Nickeling Harness Furniture, Bits, Spurs, &c. Nickeling Cast-iron Work. Nickeling Chain Work. Re-Nickeling Old Work. Nickeling Notes 301 CHAPTER XXIV. DEPOSITION AND ELECTRO -DEPOSITION OF TIN. Deposition by Simple Immersion. Tinning Iron Articles by Simple Immersion. Tinning Zinc by Simple Immersion. Tinning by Contact with Zinc. Roseleur's Tinning Solutions. Deposition of Tin by Single Cell Process. Dr. Hillier's Method of Tinning Metals. Heeren's Method of Tinning Iron Wire. Electro-deposition of Tin. Roseleur's Solution. Fearn's Process. Steele's Process. Electro-tinning Sheet Iron. Spence's Process. Recovery of Tin from Tin Scrap by Electrolysis 331 CONTENTS. X11L CHAPTER XXV. ELECTRO-DEPOSITION OF IRON AND ZINC. PAGE Electro-deposition of Iron Facing Engraved Copper-plates. Klein's Process for Depositing Iron upon Copper. Jacobi and Klein's Process. Ammonio-sulphate of Iron Solution. Boettger's Ferro- cyanide Solution. Ammonio-chloride of Iron Solution. Sulphate of Iron and Chloride of Ammonium Solution. Electro-deposi- tion of Zinc. Watt's Solution. Zincing Solutions. Person and Sire's Solution. Deposition of Zinc by Simple Immersion. Her- mann's Zinc Process . 34 CHAPTER XXVI. ELECTRO-DEPOSITION OF VARIOUS METALS. Electro-deposition of Platinum. Electro-deposition of Cobalt. Electro- deposition of Palladium. Deposition of Bismuth. Deposition of Antimony. Deposition of Lead. Metallo-Chromes. Deposition of Aluminium. Deposition of Cadmium. Deposition of Chromium. Deposition of Manganium. Deposition of Magnesium. Deposition of Silicon 348 CHAPTER XXVII. ELECTRO-DEPOSITION OF ALLOYS. Electro-deposition of Brass and Bronze. Brassing Solutions. Brunei, Bisson, and Co.'s Processes. De Salzede's Processes. Newton's Pro- cesses. Russell and Woolrich's Process. Wood's Process. Morris and Johnson's Process. Dr. Heeren's Process. Roseleur's Pro- cesses. Walenn's Processes. Bacco's Solution. Winckler's Solu- tion. American Formulae for Brassing Solutions. Thick Brass Deposits. Brass Solution prepared by Battery Process . . . 366 CHAPTER XXVIII. ELECTRO -DEPOSITION OF ALLOYS (continued). Electro-brassing Cast-iron Work. Scouring. Electro-brassingWrought- iron Work. Electro-brassing Zinc Work. Electro-brassing Lead, Pewter, and Tin Work. Observations on Electro-brassing. Bronz- ing Electro-brassed Work. French Method of Bronzing Electro- brassed Zinc Work. Green or Antique Bronze. Bronze Powders. Dipping Electro-brassed Work. Lacquering Electro-brassedWork. Electro-deposition of Bronze. Electro-deposition of German Silver. XIV CONTENTS. PAGE Morris and Johnson's Process. Deposition of an Alloy of Tin and Silver. Deposition of Alloys of Gold, Silver, &c. Deposition of Chromium Alloys. Slater's Process. Deposition of Magnesium and its Alloys. Alloy of Platinum and Silver. New White Alloys. Notes on Electro-brassing .,..,.... 379 CHAPTER XXIX. ELECTRO-METALLURGY. Application of the Term. Dechaud and Gaulticr's Process. Electro- lytic Refining of Copper by Separate Current. Elkington's Process of Refining Copper by Electrolysis. Dr. C.W. Siemens' Observations on the Electro-metallurgy of Copper. Mr. B. N. S. Keith on Refin- ing Copper by Electrolysis. M. Thenard's Experiments. Dr. Higgs' Observations. Dr. Kiliani's Observations on the Electrolytic Refining of Copper. Gramme's Experiments with Sulphate of Copper Baths 395 CHAPTER XXX. ELECTRO -METALLURGY (continued). Progress of Electrolytic Copper Refining. Copper Refining at Hamburg Copper Refining at Biache. Copper Refining at Marseilles. Electrolytic Refining at Oker. Electrolytic Refining at Birmingham. Electrolytic Refining in America. Electrolytic Treatment of Copper in Genoa. Cost of Electrolytic Refining. Arrangement of the Baths for Electrolytic Refining 416 CHAPTER XXXI. ELECTRO-METALLURGY (continued). Electrolytic Refining of Lead. Keith's Process. Electrolytic Treatment of Ores. Becquerel's Process for Treating Gold, Silver, and Copper Ores. Lambert's Process for Treating Gold and Silver Ores. Elec- tro-chlorination of Gold Ores ; Cassel's Process. Electro-metallurgy of Zinc. L6trange's Process. Luckow's Zinc Process. Electrolytic Treatment of Sulphides. MM. Bias and Meist's Process. Werder- mann's Process , , , . . , . . 428 CONTENTS. XV CHAPTER XXXII. MECHANICAL OPERATIONS CONNECTED WITH ELECTRO-DEPOSITION. TAGB Metal Tolishing.- Brass Polishing. The Polishing Lathe. Brass Finishing. Lime Finishing. Nickel Polishing and Finishing. Steel Polishing. Polishing Silver or Plated Work. Burnishing. Burnishing Silver or Plated Work. Electro-gilt Work . . . 451 CHAPTER XXXIII. RECOVERY OF GOLD AND SILVER FROM WASTE SOLUTIONS, &c. Recovery of Gold from Old Cyanide Solutions. Eecovery of Silver from Old Cyanide Solutions. Extraction of Silver by the Wet Method. Eecovery of Gold and Silver from Scratch-brush Waste. Kecovery of Gold and Silver from Old Stripping Solutions .... 461 CHAPTER XXXIV. AUXILIARY OPERATIONS CONNECTED WITH ELECTRO - DEPOSITION. Stripping Metals from each other. Stripping Solution for Silver. Cold Stripping Solution for Silver. Stripping Silver from Iron, Steel, Zinc, &c. Stripping Silver by Battery. Stripping Gold from Silver Work. Stripping Nickel -plated Articles. Stopping-off. Applying Stopping-off Varnishes. Electrolytic Soldering . . 466 CHAPTER XXXV. MATERIALS USED IN ELECTRO -DEPOSITION. Acetate of Copper. Acetate of Lead. Acetic Acid. Aqua Fortis. Aqua Eegia. Bisulphide of Carbon. Carbonate of Potash. Caustic Potash. Chloride of Gold. Chloride of Platinum. Chloride of Zinc. Cyanide of Potassium. Dipping Acid. Ferro- cyanidc of Potassium. Hydrochloric Acid. Liquid Ammonia. Mercury, or Quicksilver. Muriatic Acid. Nickel Anodes. Nickel Salts. Nitric Acid. Phosphorus. Pickles. Plumbago. Pyro- phosphate of Soda. Sal-ammoniac. Sheffield Lime. Solution of Phosphorus. Sulphate of Copper. Sulphate of Iron. Sulphuric .Acid. Trent San i . . ... . . . . . ...475 XVI CONTENTS. CHAPTER XXXYI. USEFUL INFORMATION. PAGE Driving Belts. Chatter's Dynamo-electric Machine. Quantity of Elec- tricity and Electro-motive Force. Management of Dynamo-electric Machines. Management of Batteries. Relative Power of Batteries. Constancy of Batteries. Relative Intensity of Batteries. The Resistance Coil. Speed Indicator. Binding Screws. Character- istics of Metals. Test for Free Cyanide. Oxidising Copper Sur- faces. Alloys. Soldering. Soldering Liquid. To remove Soft Solder from Gold and Silver Work. Platinising. Steel-facing Copper-plates. Antidotes and Remedies in Cases of Poisoning . 487 APPENDIX. Electro- deposition of Platinum (Thorns' Process). Electro-deposition of Aluminium and its Alloys (Burghardt and Twining's Process). Electrolytic Treatment of Zinc and its Ores (Watt's Process). Electro-deposition of Cobalt. Sulphate of Cobalt. Double Sul- phate of Cobalt and Ammonium. Chloride of Cobalt. Chlorides of Cobalt and Ammonium. Chlorides of Cobalt and Sodium. Double Sulphates of Cobalt and Ammonium, with Chloride of Sodium added, Professor Silvanus Thompson's Cobalt Process. Removing Tin from Tinned Iron. Garcia's Process. Montague's Processes. Electrolysis of Lead Salts. Phosphate of Lead in Caustic Potassa. Peroxide of Lead Colourations. Crystalline De- posits of Lead. Electro-deposition of Iron. Protosulphate of Iron Bath. Ammonio-Sulphate of Iron. Citrate of Iron. Double Sul- phate of Iron and Potassa. Persalts of Iron. Electro-deposition of Alloys: Colouration and Staining of Metals. Colouring Nickel- plated Work. Colouring or Staining of Brass Surfaces. Crystals of Metallic Tin. The Gulcher Rheostat. Seamless Metal-coated Tubes 513 USEFUL TABLES: i. Elements, their Symbols and Atomic Weights. 2. Relative Conductivity of Metals. 3. Specific Resistance of Solutions of Sulphate of Copper. 4. Specific Resistance of Solu- tions of Sulphate of Copper at 50 Fahr. 5. Table of High Tem- peratures. 6. Comparative French and English Thermometer Scales. 7. Birmingham Wire Gauge for Sheet Copper and Lead. 8. New Legal Standard Wire Gauge. 9, 10. Chemical and Elec- tro-chemical Equivalents. ii. Tables of Weights and Measures . 543 LIST OF WORKS RELATING TO ELECTRO-DEPOSITION . . '.551 ELECTRO-DEPOSITION, CHAPTER I. HISTORICAL REVIEW OF VOLTAIC ELECTRICITY. Galvani's Discovery. Volta's Discovery. Simple Voltaic Circle. The Voltaic Pile. Cruickshank's Trough Battery. Dr. Babbington's Battery. Volta's Couronne des Tasses. Dr. Wollaston's Battery. DanielPs Battery. Smee's Battery. Grove's Battery. Compound Grove Battery. Callan's Iron Battery. Bunsen's Battery. Walker's Graphite Battery. Leclanche's Battery. Bichromate Battery. Marie-Davy Battery. Secondary Batteries, or Accumulators. FEOM the date of the discovery of Voltaic Electricity, or Voltaism, in the year 1799, experimental philosophers in all parts of the world un- ceasingly devoted their labours to the investigation of the phenomena which the electric current, generated by chemical action upon metals, is capable of producing, until, step by step, the great Art of Electro - Metallurgy was called into existence, and brought to its present high state of development. Before entering into the numerous applications of current electricity in the deposition of metals upon each other, or upon other conducting surfaces, it will be interesting and instructive to consider how this remarkable force was discovered, and the various means which have been adopted to bring it under our control as an agent of practical utility. It has long been the custom to confound the terms voltaism and galvanism, voltaic battery and galvanic battery, in relation to the electric current produced or evolved by the action of chemical substances upon metals of opposite character, but we think it is quite time that the conventional error should be rectified, more especially for the advantage of those who may be entering into the study of electrical phenomena for the first time. G-alvani's discovery which was of a purely accidental nature in no respect resembles that of his equally illustrious fellow-countryman, Volta ; but since it undoubtedly led to the still more important discovery of what has been termed chemical electricity that is, electricity obtained by the action of acids, 2 HISTORICAL REVIEW OF VOLTAIC ELECTRICITY. o > n c c . 4 a o '* Fig. 6, in which the plates were let into grooves formed in a shallow wooden trough, the separate rows of plates being connected (as shown by the curved wires) by a short conducting wire, while a length of copper wire was attached to each ter- minal plate of the series, forming the positive and negative wires respectively. Fig. 7. The plates were excited by a dilute solution of sulphuric acid. This battery created considerable interest at the time, and afforded experi- mentalists the means of pursuing their investigations in current elec- tricity with greater facility than was possible with the pile. It may fairly be considered the first really practical compound circle, or battery, that had been produced up to that period. Although this was a considerable improvement upon the pile, however, there was BABBINGTON S BATTERY. 7 some inconvenience in removing the exhausted acid solution, and this suggested a further improvement, for which we are indebted to Dr. Babbington. Dr. Babbington's Battery. This battery (Fig. 7) consists of eight or more pairs of copper and zinc plates, usually about 4 inches square, each pair being united by soldering at one point only. The trough, which contains as many cells as there are pairs of plates, is generally made of earthenware, and the plates are attached to a bar of wood, by which arrangement the plates may be withdrawn from the exciting fluid (dilute sulphuric acid, for instance) when the battery is not required for use. It is necessary that the bar of wood should be per- fectly dry, and coated with varnish in order to render it non-con- ductive of electricity. Volta's Couronne des Tasses. Still pursuing the subject, Volta afterwards invented an arrangement, to which he gave the name couronne des tasses (crown of cups) which was exceedingly simple and effective. This consisted of a row of glasses or cups, each containing Z C z c z c z c Fig. 8. dilute sulphuric acid. Zinc and copper plates, about 2 inches square, are connected by a copper conducting wire (which may be con- veniently attached by soldering), and the plates are immersed in the cups in the following order (see Fig. 8) : the zinc plate z of one pair is immersed in one of the cups, and the copper c in the next cup. Another zinc plate is then placed in this second cup, but not touching the copper plate, and its connected copper plate immersed in a third cup, in which again another zinc plate is immersed, and so on, through the whole series, the metals being arranged alternately, zinc and copper, zinc and copper, until the entire number of vessels are supplied with one pair of opposite metals. It will thus be seen that, regardless of the number of pairs, the last plate at one end will be zinc, and at the other, copper. The direction of the current is from the zinc to the copper. If the zinc plates be amalgamated, as before mentioned, by which the chemical action of the acid solution upon the zinc is prevented, except when the circuit is complete, either by contact of the terminal wires, or by being immersed in a solution which is a 8 HISTORICAL EEVIEW OF VOLTAIC ELECTK1CITY. conductor of electricity, we shall observe that the moment we bring the wires in contact, a violent effervescence occurs at each of the copper plates, which instantly ceases when the wires are again sepa- rated. If glasses are employed in this arrangement, we can readily observe the interesting excitement which is brought about in each vessel the moment contact is made between the terminal wires, and this lesson will explain to us what must and does take place in all voltaic arrangements, no matter what may be the metals or elements employed in the construction of the battery. Dr. Wollaston's Battery. An important improvement in the pre- ceding arrangements, but more directly in the battery designed by A Dr. Babbington (Fig. 7), was the ^ & 2B famous battery constructed by Dr. "Wollaston in 1815, in which the copper plates were doubled, as in Fig. 9, by which each surface of the zinc plates became opposed to a surface of copper, whereby a con- siderable increase of electric energy was obtained. The original form of this battery, as shown in the en- graving, consisted of a bar of wood A, to which the plates are screwed. B B are the zinc plates, connected as usual with the copper plates, c c, which are doubled over the zinc Fig. 9. plates, and opposed to them in every direction ; but the contact of their surfaces is prevented by pieces of wood or cork placed between them. When in use, the plates are lowered into a wooden trough con- taining a solution of sulphuric and nitric acids one part of each acid to sixty parts of water. This important improvement in voltaic batteries led to the discovery, by its gifted inventor, that by increasing the copper surface, the quantity of electricity was greatly augmented one of the most valuable facts that had yet been made known in connection with voltaism. Daniell's Battery. Another remarkable advance in the construction of voltaic circles was due to Professor Daniell, who, in 1836, contrived his celebrated Constant flattery, a description of which appears in the Philoso- phical Transactions, 1836, p. 117, and runs as follows: "A cell of this battery (Fig. 10) consists of a cylinder of copper 3 1 inches in diameter, which experience has proved to afford the most advantageous distance between the generating and conducting Fig. 10. SMEE S BATTERY. surfaces, but which may vary in height according to the power it is wished to obtain. A membranous tube, formed of the gullet of an ox, is hung in the centre by a collar and circular copper plate resting upon a rim placed near the top of the cylinder ; and in this is sus- pended, by a wooden cross-bar, a cylindrical rod of amalgamated zinc, half an inch in diameter.* The cell is charged with a mixture of 8 parts of water and I part of oil of vitriol, which has been saturated with sulphate of copper ; and portions of the solid salt [crystals] are placed upon the upper copper-plate, which is perforated like a colander, for the purpose of keeping the solution always in a state of saturation. The internal tube is filled with the same acid mixture, without the copper. A tube of porous earthenware may be substituted for the membrane, with great convenience, but probably with some little loss of power. A number of such cells admit of being connected together very readily into a compound circle, and will maintain a perfectly equal and steady current for many hours to- gether, with a power far beyond that which can be produced by any other arrangement of a similar quantity of metals." The introduction of this remarkable, voltaic battery established an important era in electro- chemical history, not only on account of its practical merit as a generator of current elec- tricity of great constancy, but from the possi- bility, if not probability, of its having indirectly led to the discovery of the electrotype process, upon which, as we have shown elsewhere, the whole art of electro -deposition is founded. Smee's Battery. Another valuable addition to the series of voltaic circles or batteries already known was invented by Mr. Alfred Smee, to whom, more than any other, the early electro -metallurgists were indebted for a clear exposition of the principles of the art, at a time when, being in its infancy, effects, rather than causes, occupied the * In this battery the local action of the sulphuric acid on the zinc is prevented by its amalgamation, which causes a film of hydrogen to adhere to it so long as the circuit is incomplete. When complete this hydrogen goes over to the copper, and by adhering to it interferes with the passage of the electricity ; but the presence of the oxide of copper of the sulphate [of copper] tends by secondary action to get rid of this hydrogen, which is employed in reducing the oxide ; and successive films of metallic copper are thus thrown down upon the copper, and a clean metallic surface always preserved ; while the deposition of copper upon the zinc plate (which would cause numerous secondary circles) is prevented by the diaphragms [ox gullets]. Fig. ii. 10 HISTORICAL REVIEW OF VOLTAIC ELECTRICITY. attention of its practical followers. Smee's battery, Fig. n, consists of a pair of amalgamated zinc plates, with a plate of thin sheet- silver coated with black deposit of platinum (by which a permanent rough surface is obtained, which favours the escape of the hydrogen). The plates are supported by a bar of wood, and are furnished with binding- screws for connecting the conducting wires. The parts of the battery may be thus described : i, an earthenware or glass vessel containing dilute sulphuric acid (i part acid to 7 parts of water) ; 2, the bar of wood to which the platinised silver plate is attached ; 3, the two plates of amalgamated zinc, secured to the wooden bar by the binding -screw or clamp ; 4, a second binding -screw connected by means of solder to the silver plates. Grove's Battery. In the year 1839, Professor Grove (the present eminent judge), invented the most powerful voltaic battery known, in Fig. 12. which the elements are zinc and platinum, excited, respectively, by sulphuric acid and nitric acid. This famous battery, which is commonly known as the " Nitric Acid Battery," or " Grove's Battery," consists of a flat cell of glazed porcelain, inside which is another cell of similar shape but smaller and thinner, composed of porous (that is unglazed) BUNSEN S BATTERY. II earthenware. A flat plate of zinc is bent in such a form that the porous cell may be placed within its folds, by which a surface of zinc is exposed to each side of the inner cell. A plate of thick platinum foil is inserted in the porous cell, and is of sufficient length to be attached to the projecting end of the zinc plate by means of a binding - screw or clamp. The inner porous cell is charged with strong nitric acid, and the outer vessel with a mixture composed of I part of oil of vitriol to 6 parts water. The zinc plate is well amalgamated. Compound Grove Battery. In the accompanying engraving, Fig. 12, is shown a single and also a compound arrangement of four cells of the battery. A a is the bent zinc plate, B the platinum plate in the porous cell. At c is another platinum plate to show how it is to be connected to a second zinc plate when more than one cell of the battery is to be employed. D is a glazed porcelain vessel containing a series of four pairs of metals connected by clamps and binding- screws ; the two latter (furnished with copper conducting wires) are connected, one to the terminal zinc plate at E, and the other to the platinum element at the opposite end of the series. Although an exceedingly powerful battery and admirably suited for exhibiting the effects of voltaic or current electricity, Grove's battery is not well adapted to the purposes of electro -deposition, owing to its costliness both in construction and use; its importance in scientific research, however, cannot be over- estimated. Callan's Iron Battery. Another remarkable battery was invented by Dr. Callan, and termed by him the Maynooth battery. This con- sisted of a cast-iron cell charged with a mixture composed of twelve parts of concentrated nitric acid and eleven and a half parts of strong oil of vitriol. A porous cell, containing a plate of zinc and a solution of nitric and sulphuric acids, was placed in the centre of the iron cell, and a binding screw was attached to the iron cell, as also one to the zinc plate, when the battery was complete. Dr. Callan constructed a series of such circles consisting of 557 pairs, containing 96 square feet of zinc and about 200 square feet of cast-iron. The discharge of this powerful battery through a very large turkey in- stantly killed it, and a luminous flame (or arc] was produced 5 inches in length. The iron battery, though very interesting and useful for experimental purposes, is not suited for electro -deposition. Bunsen's Battery. One of the most useful batteries for the practical purposes of the electro -metallurgist was invented by the gifted Chevalier Bunsen, the 'elements of which are zinc and carbon (graphite). As in the case of Grove's battery the exciting fluids are, for the zinc, dilute sulphuric acid (oil of vitriol), and for the carbon strong nitric acid. The modern form of the battery is shown hi Fig. 13. The outer vessel is a cylindrical stoneware jar capable of 12 HISTORICAL REVIEW OF VOLTAIC ELECTRICITY. holding about 4 gallons (though, of course, smaller cells maybe used). A plate of stout sheet zinc is turned up in the form of a cylinder, A, and this is well amalgamated with mercury. A suitable binding screw is attached to this cylinder to receive the conducting wire. A porous cell, about 3 J inches in diameter, is placed within the zinc, and in this a block of gas carbon (obtained from the linings of old and much -used gas retorts) is furnished with a suitable clamp B for attaching a conducting wire, and the block is then gently deposited in the porous Fig. 13. Bunsen's Battery. cell. This cell is then nearly filled with strong nitric acid, and the outer vessel is next filled to the same height as the nitric acid in the porous cell, with dilute sulphuric acid about i part acid to 10 parts water, when the arrangement is complete. This battery is ex- ceedingly powerful, and is much employed in many of the processes of electro-deposition. In the original form of Bunsen battery a cylindrical block of carbon was employed, but, since it was difficult to obtain these cylinders from gas carbon, Bunsen adopted the following method of preparing them WALKER S BATTERY. 13 artificially : A quantity of well-baked coke and pit coal was ground to a fine powder and the mixture heated over a low charcoal fire, in sheet-iron moulds, or in the form of hollow cylinders, by introducing into the iron mould a cylindrical wooden box and filling with the mixture the space between the two walls of the mould. To render the porous mass compact it was plunged into a concentrated solution of sugar, and then dried until the sugar had acquired a solid con- sistence. It was then exposed, for several hours, to a very intense white heat in a covered vessel, and afterwards allowed to cool gradually. The original form of this battery and its dissected parts are shown in Fig. 14. The carbon cylinder carries a collar at its upper part, upon which may be deposited a stout coating of copper in the electro typing bath, and to this a strip or band of sheet copper may be attached, by means of soldering, to form the conducting medium, a similar strip of copper being connected to the zinc cylinder Fig. 14. of the battery. The copper deposited upon the carbon should be well varnished with black japan varnish, so as to protect it from the action of the nitric acid used as the exciting fluid in the porous cell. The outer vessel being nearly filled with dilute sulphuric acid, and the porous cell with nitric acid both exactly at the same level the battery is then ready for work, and is undoubtedly one of the most useful of all voltaic circles. Walker's Graphite Battery. The late Mr. C. V. Walker intro- duced a modification of Smee's battery (page 9), in which he substi- tuted plates of platinised graphite (carbon) for platinised silver, by which an exceedingly effective battery is produced. These batteries have been very extensively used in working the telegraph system of the South-Eastern Railway, and may be advantageously employed in electrotyping. The carbon plates are either cut from the graphite obtained from exhausted gas retorts (the best material for the purpose), or they may be substituted by artificially prepared carbon 14 HISTORICAL REVIEW OF VOLTAIC ELECTRICITY, which is now being sold for this and other similar purposes. Mr. Walker thus describes his graphite battery : Having obtained the plates, the first operation is to prepare a mixture of one part sul- phuric acid, and four parts water, and to let the plates lie in this for at least a couple of days and nights. This operation will clean them from all foreign matter that is soluble in sulphuric acid. They are now to be rinsed in plain water, and set to dry. Each plate is then to have a hole drilled in it, in order to receive a rivet. The top of the plate is now to be protected with varnish on either side of the rivet hole, and on both sides of the plate. An unvarnished part of about an inch in width, and on both sides, is to be left in the middle, having the rivet-hole in the centre. Electrotype copper is now to be de- posited upon the part that is left unvarnished (by any of the processes hereafter described). The object of coppering this part of the plate is to enable a strip of copper to be soldered to it, which could not be effected upon the graphite surface. A strip of copper, about 6 inches long, is then tinned, by moistening it with a solution of chloride of zinc (zinc dissolved in muriatic acid), and applying pewter solder by means of a soldering iron. The object in tinning the surface of the copper is to prevent the acid from acting upon it. The copper de- posited upon the graphite is also tinned in the same manner. The next operation is to attach the slip of copper to the graphite plate. This is done by means of a copper rivet, previously tinned, and then by means of a soldering iron. A strong and perfect connection is thus obtained. The plate is next to be platinised by the process given in another chapter, after which the top of the plate and the copper strip are to be thoroughly coated with varnish. Fig. 15 represents three cells of the graphite battery, as employed for telegraph pur- poses. The cells are stone jars, holding a pint or a quart ; the zinc plates, which are well amalgamated, are placed with their foot in a "slipper" made of gutta-percha, in which mercury is placed, the BICHROMATE BATTERY. 15 object of which is to keep the plates constantly amalgamated. The reader will observe how closely the arrangement of the plates re- sembles Volta's couronne des tasses. The exciting fluid, as in the Smee battery, is dilute sulphuric acid. Besides the more important voltaic batteries referred to, numerous other arrangements have been devised, but since most of these are of little applicability in electro-deposition, a mere passing reference to some of the more striking modifications will be sufficient to show how varied are the means by which voltaic electricity may be generated. It had been proved, as we have shown, that water alone was capable of generating a current of intensity electricity, and this led to the con- struction of a battery which received the name of the water battery. Mr. Pepys had such a battery constructed of 2,000 pairs, which was capable of giving a shock resembling that from the Ley den jar employed in receiving electricity from an electrical machine. Mr. Crosse and Mr. Gassiot constructed a still more extensive water battery, consisting of 3,520 pairs, which were cylinders of zinc and copper, separated by string. The exciting liquid was distilled water. In this arrangement, sparks were found to pass before contact of the terminal wires, or poles, was made, which proves that the current more resembles that obtained by friction (as from an electrical machine"; than from a voltaic circle. It is in fact an intensity current, with buf little of the quality termed quantity, and therefore represents current electricity in its weakest form. Leclanche's Battery. A battery which has been extensively adopted for electric bells, and is now being much used as a substitute for the Daniell battery and for telegraphic purposes, is the Leclanche battery. It consists of an outer glass vessel in which the zinc element (a rod of zinc) is immersed in a solution of sal ammoniac (chloride of ammonium], A porous cell stands in the centre of the vessel, and in this is placed a plate of carbon, surrounded by a mixture of peroxide of manganese and carbon in coarse grains. This battery is very con- stant in its action. Its inventor, M. Leclanche, of Paris, lays great stress upon the importance of employing very pure peroxide of man- ganese. Tfce Bichromate Battery, for experimental purposes, is a very energetic and agreeable voltaic arrangement, and, unlike the batteries in which nitric acid is used, it gives off no pungent fumes. The battery, which is represented in Fig. 16, consists of a glass wide- mouthed bottle, filled nearly up to its neck with a solution of bichro- mate of potash, to which sulphuric acid is added. The solution is thus prepared : A saturated solution of the bichromate is first pre- pared, by dissolving about 3 ozs. of bichromate of potash in a pint of boiling water. When quite cold, add about i^ ozs. of oil of vitriol. i6 HISTORICAL REVIEW OF VOLTAIC ELECTRICITY. when the liquid will acquire a considerable degree of heat. The liquid must be again allowed to cool, when it is ready to be poured into the bottle. The mechanical arrangement of the battery consists of a wooden cap, turned so as to fit into the bottle, like a cork, but not too tightly. Two plates of carbon are connected by a couple of binding - screws to the cap, and between this pair of plates a square plate of zinc, connected by a rod to the centre binding- screw, is placed, the rod passing through a round hole in the centre of the cap, so that the zinc plate may be raised out of the liquid into the empty neck of the bottle when the battery is not required for use. Marie-Davy Battery. An ingenious modifica- tion of several of the voltaic circles before named is that known as the Marie-Davy battery ; but its employment is chiefly in connection with tele- graphy. The elements are zinc and carbon (gra- phite plates), and these excited by moistened bisulphide of mercury, the zinc plates being amalgamated, and the graphite plate platinised, as in Walker's battery. A section of this battery is shown in Fig. 17, in which a is the platinised graphite, b b the bisulphide of mercury, c a circular zinc plate, and d a porous cell. Secondary Batteries or Accumulators. Volta ob- served that when a piece of moistened paper was placed upon a strip of glass, and caused to complete the circuit of a vol- taic battery, that it was found to become electro-polar, that is to say, that half which was in contact with the positive ex- tremity of the battery became positive, while the portion at the negative end became negative ; and this electrical condition of the paper continued for some lg ' I7 * time after its separation from the poles of the battery, provided that the insulation were maintained. This is termed polarisation . The sub j ect was afterwards further invest gated, but no practical application of the fact seems to have taiep SECONDARY BATTERIES. I 7 place until Plante formed his now famous " secondary battery," in 1860, based upon the powerful affinity which exists between peroxide of lead and hydrogen, a fact first noticed by De la Rive. Plante's battery is constructed as follows : It consists of nine elements, presenting a total surface of ten square metres, each element being formed of two large lead plates rolled into a spiral, and separated by coarse cloth, and immersed in water acidu- lated with one -tenth of sulphuric acid. The kind of current used to excite this battery depends on the manner in which the secondary couples are arranged. If they are arranged so as to give three ele- ments of triple surface, five small Bunsen cells, the zincs of which are immersed to a depth of seven centimetres, are sufficient to give, after a few minutes' action, a spark of extraordinary intensity when the current is closed. The apparatus, in fact, plays the part of a con- denser, for by its means the work performed by the battery, after the lapse of a certain time, may be collected in an instant. This secondary battery has since been greatly improved by Faure, Sellon, and others, and during the past few years secondary batteries have been very extensively adopted in connection with electric lighting, and even for the purposes of electro -deposition. When it is desired to keep the baths at work during the night, as when depositing thick coatings of copper, without running the dynamo, accompanied by the necessary attendance, the secondary batteries are charged, and being put in connection with the work and anodes in the tanks, are left to quietly yield up their current and continue the deposition until the following morning. Secondary batteries are extensively manufactured by the Electric Storage Company, London, and will doubtless be adopted by many electro-depositors to perform useful night work. In the preceding pages we have directed attention more especially to the principal modifications of voltaic couples or circles, to which Volta's splendid discovery gave rise ; we may state, however, that many other more or less ingenious batteries have been devised, but since most of these are ill-suited to the purposes of electro-depo- sition, a detailed description of them may be conveniently omitted. Indeed, we may say, as regards those voltaic couples to which we have referred, that for all practical purposes of the electro-depositor of metals or, if we may so designate him, electrolysist the voltaic batteries of Daniell, Smee, Wollaston, Grove, and Bunsen will fulfil all his requirements. CHAPTER II. ELECTRO-MAGNETISM. MAGNETO -ELECTRICITY. DYNAMO-ELECTRICITY. Oersted's Discovery. Electro-magnetism. The Galvanometer. Electro- magnets. Magneto-electricity. Saxton's Magneto-electric Machine. Woolrich's Magneto-electric Machine. Wilde's Magneto-electric Ma- chine. Gramme's Magneto-electric Machine. Dynamo-electricity. Siemens' Dynamo-electric Machine. Weston's Dynamo-electric Ma- chine. Gulcher Dynamo-electric Machine. Crompton's Dynamo- electric Machine. Schuckert's Dynamo-electric Machine. Mather's Dynamo-electric Machine. Oersted's Discovery. In the year 1819, Professor Oersted, of Copen- hagen, made the important discovery that magnetism cotildbe produced by electricity, and it will be necessary to give a brief resume of the prin- cipal facts connected with this great discovery before treating of other discoveries to which, in course of time, it gave rise. It had never been believed that an electrified wire that is, the wire which conveys the current from a voltaic battery and a magnetised needle (as the needle of an ordinary mariners' compass) had any mutual influence ; it was considered merely the means of conveying, or conducting, the voltaic current, and nothing more. Oersted proved, however, that while a voltaic current is passing through the conducting wire, it has the power of attracting and repelling a magnetic needle placed beneath it. Electro -Magnetism. If the needle be allowed to assume its natural direction, and a straight portion of the electrified wire then held above and parallel to it, the pole of the needle which is next to the negative end of the battery (the wire connected to the zinc) moves towards the west; if it be below the conducting wire the same pole moves towards the east. This striking phenomenon may be illus- trated by taking a piece of copper wire (ordinary bell- wire, for ex- ample) about eighteen inches long, and connecting one end of it, by means of solder, to a strip of amalgamated zinc, the other end being connected in the same way to a strip of platinum or silver. The wire must be bent in the form indicated in Fig. 18. If the plates be now placed in a small glass or jar, and a magnetic needle (a pocket compass will do) placed beneath the lower bend of the wire and exactly parallel to it, no change will be observable ; if, however, we now pour water Fig. 18. THE GALVANOMETER. 1 9 acidulated with sulphuric acid into the glass, the needle will be at once deflected, or turned from its course, and exhibit a tremulous motion, .as though under some irritating influence, j There is not stronger evi- I dence of the development V. of an invisible force, by the chemical action which takes place in the cell, than is produced by the motion of the needle under the influence of the copper wire through which that force is passing. The Galvanometer. The above important fact led to the construc- tion of a most valuable instrument for detecting the presence of voltaic or current electricity and measuring its intensity, and is termed a galvanometer. These instruments are manufactured with great delicacy and are constantly employed by electricians and telegraphists. When the voltaic current passes above and below the needle at the same time and in opposite directions, the deflection of the needle is more powerful, for the current passing through the wire above the needle conspires, equally with the current passing along the wire below, to deflect the needle from its normal position and to bring it into a new position nearer at right angles to the plane of the wire. Taking advantage of these facts, Schweigger first conceived the idea of utilising them as a means of detecting the presence of current elec- tricity. The simplest form of galvanometer is shown in Fig. 19. It consists of a magnetised needle so poised as to be affected by the cur- rent passing above and be- neath it. N s indicate the north and south poles of the needle, and the darts explain the direction of the current, from its first entry at P to its Fig. 19. exit at N. The two small copper or brass cups are for the reception of mercury for the purpose of connecting the wire with the voltaic battery or other source of the electric current. Another important fact in connection with Oersted's fundamental discovery, is that an electrified wire not only possesses the power of turning the magnetic needle from its natural position, but it can also ELECTRO-MAGNETISM. affect contiguous wires ; moreover, the effects above described can be multiplied by multiplying the convolutions of the wire, and if the wire be insulated so as to prevent the escape of the current laterally, by covering it with silk, the delicacy of the arrangement in detecting weak traces of the current is greatly increased. If, in- stead of the needle being supported upon a pivot, as in Fig. 19, it be suspended by a thread of fine silk or filament of spun glass, as suggested by Eitchie, its sensi- bility is further increased. The sensibility of the instrument is still further augmented by employing two needles, one above and one within the coil, and placed parallel, but with their poles reversed, whereby the magnetic influence of the earth is neutralised. There are many forms of the galvanometer, but they all consist essentially of a compass needle, with one or more strands of covered, that is insulated, copper wire surrounding it, and arranged in the 13 Fig. 22. Fig. 21. same direction as the needle, the two ends of the wire being connected to two binding -screws, to which the terminals of the battery, or other source of the electric current, are attached when the instrument is in use. A common form of galvanometer is shown in Fig. 20, and a still more convenient instrument in Fig. 2 1 . Having thus shown how the electric current, traversing copper wire, influences the position of a magnetic needle, let us now see what effect it will have upon iron. To illustrate this, we will take the same simple voltaic circle as before (Fig. 18), but in place of the naked straight wire employed in the former case, we will take a length of covered copper wire and form it into a helix, or coil, as in the accom- panying cut, Fig. 22. Now, if we pass a small rod of iron through MAGNETO-ELECTRICITY. 2 1 the coil, and then pour dilute sulphuric acid into the glass cell, we shall find, on bringing an ordinary steel needle, or iron filings near the projecting end of the iron rod, that they will be attracted by it, showing that the iron has become magnetic. On removing the rod, however, the iron will be found at once to lose its magnetic property , for the filings will instantly fall from it. If the rod be replaced in the helix it will again become magnetic. From this it is evident that an insulated wire through which an electric current passes acquires a temporary magnetic property ; and the fact may be more fully demonstrated in the following way. Electro-Magnets. A bar of soft iron is bent in the form of a horse- shoe, as in Fig. 23. Covered copper wire is now twisted round the bar, as in the illustration, and the two ends of the wire are connected to a voltaic battery, as a Smee or Daniell battery, for example. If, now, a bar of iron be brought near the two poles of the artificial magnet thus formed it will be at once attracted to them ; and if the current have sufficient power, this will be capable of sustaining an additional weight. Indeed, such electro-magnets, as they are termed, have been con- structed which were capable of sustaining many hundreds of pounds weight. The magnetic state established in the way described is termed indttced magnetism, to distinguish it from the permanent magnetic condition of steel bar or horse-shoe magnets with which all are familiar. We J &' 2 3- thus see how Oersted's fundamental discovery led up to the invention of the galvanometer and the construction of electro-magnets. Magneto-Electricity. In the year 1831, Michael Faraday one of the most brilliant observers of the present century had been en- gaged in investigating the phenomena above referred to, when it occurred to him, since magnetism could be produced by electricity, that magnetism in motion ought to produce an electric current, and in order to verify his conclusion, he adopted the following device : A long spiral coil of covered copper wire was connected by its ends to a galvanometer, which would, of course, indicate a current of electricity in the helix and wires connected with it ; he found that in the act of introducing the pole of a powerful bar magnet within the coils of the spiral, a deflection of the galvanometer needle took place, in one direction, and in the act of withdrawing it, took place in the opposite direction ; so that each time the conducting wire cut the magnetic curves, a current of electricity was for the moment produced in it. He subsequently had a copper disc (Fig. 24) mounted so that it could be made to revolve upon its own axis between the poles of a powerful horse-shoe magnet ; a conducting wire w was placed in contact with the axis of the copper disc, and a second wire w' was put in contact 22 MAGNETO-ELECTRICITY. with the circumference of the disc. The terminals of the wires are shown dipping into the mercury cups of a galvanometer g, and the darts indicate the direction of the current. N s represent the north and south poles of the magnet. When the copper disc is made to revolve from right to left, a current of electricity is produced in the direction of the darts, and the galvanometer needle is at once de- flected ; if, however, the disc is made to revolve in the opposite direc- tion, or if the poles of the magnet are reversed, the electric current moves in an opposite direction. Not only did Faraday obtain indications of an electric current by the galvanometer under the above conditions, but by another modifi- cation of the arrangement, in which the current was induced by an electro-magnet, he succeeded in obtaining an electric spark. Subse- quently, Nobili and Antinori, and in this country Professor Forbes, Fig. 24. obtained a spark from a permanent magnet. For this purpose a helix of insulated copper wire was formed round the middle of the soft iron keeper (or armature) of a powerful horse-shoe magnet ; on making and breaking contact between the keeper and the magnet, magnetism was alternately created and destroyed within it, and at these periods of transition, electric currents were induced in the helix, and on so arranging the conducting wires as at these moments to make and break contact with mercury, a brilliant spark was observed at each motion of the keeper. It was afterwards found that by causing the poles of a powerful horse -shoe magnet to revolve rapidly before a soft iron armature covered with insulated wire, or by a still better arrangement to make the armature revolve before the poles of the SAXTON S MAGNETO-MACHINE. 23 magnet, an electric current was obtained possessing sufficient power to render iron wire red hot. Thus the foundation was laid for the con- struction of still more powerful contrivances, which, in due course, were produced, the first of which was invented by Pixii, of Paris, and first made known at a meeting of the Academy of Sciences on September 3rd, 1832. In June of the following year, Mr. Saxton introduced an improvement on Pixii's machine, which, in 1835, he further improved by adding to the machine a double armatiire. With this machine he could not only produce brilliant sparks and give powerful shocks, but it was found very effective in chemical decomposition. The following description of this machine is thus given by Professor Daniell, and since it was the first really practical magneto -electric machine, its introduction here will be both interesting and instructive. Saxton 's Magneto-electric Machine. A very powerful horse- shoe magnet, formed of numerous steel plates [a compound magnet] closely applied together, or an electro -magnet of soft iron of the same form, is placed in a horizontal position. An armature or bar of the purest soft iron has each of its ends bent at a right angle, and is mounted in such a way that the surfaces of those ends are directly opposed and close to the poles of the magnet ; in this position it may be made to rotate rapidly in a vertical direction by means of multiply- ing wheels and an endless band. Two series of copper wires, covered with silk, are wound round either end of this bar as compound helices. The extremities of these wires, having the same direction, are con- nected together and with a small circular disc, rotating with the armature in a cup of mercury, with which it is, therefore, in metallic communication in every position of the disc. The other extremities of the wires are united together, and, passing without metallic con- tact through the spindle upon which the apparatus turns, terminate in a small slip of copper with two opposite points placed at right angles to the axis. These, in the act of rotation, alternately dip into and rise above the mercury in another cup, which may be connected with the first at pleasure by means of a copper wire. By the laws of magnetic induction the armature becomes a temporary magnet when- ever its bent ends are opposite the poles of the magnet, and ceases to be magnetic when they are at right angles to them. The momentary generation and destruction of the magnetic force, which will be oppositely directed in the bar as its opposite ends become opposed to the same poles in the act of rotation, must, by the laws of magneto - electric induction, induce corresponding opposite electric currents in the copper wire, if the circuit be complete, by the immersion of the points at the moment of their passage. The points are so arranged that, standing nearly at right angles to the revolving bar, they just rise from the mercury as its ends become opposed to the poles of the 24 MAGNETO-ELECTRICITY. magnet, and, the circuit being thus suddenly broken at the moment of the electric wave, the current passes in the form of a brilliant spark. An illustration of Saxton's magneto -electric machine is shown in Fig. 25, of which the following description is given in Noad's " Text-Book of Electricity" : * "A is a compound horse -shoe magnet, composed of six or more bars, and supported on the rests b e, which are screwed firmly on the board B D ; into the rest e is screwed the brass pillar c, carrying the wheel/, having a groove in its circumference and a handle by which it can readily be revolved on its axis. A spindle passes from one end Fig. 25. Saxton's Magneto-Electric Machine. of the magnet to the other, between the polc.-> and projects beyond them about three inches, where it terminates in a screw at k, to which the armatures, to be described immediately, are attached ; at the farther extremity is a small pulley, over which a gut band passes, by means of which, and the multiplying wheel /, the armatures can be revolved with great rapidity. " The armatures, or inductors, as seen at F, are nothing more than electro-magnets. Two pieces of round iron are attached to a cross- piece, into the centre of which the spindle h screws. Round each of these bars is wound, in a continuous circuit, a quantity of insulated * " The Student's Text-book of Electricity. Ac. Edited by W. H. Preece, M.I.C.E. By Henry M. Noad, F.R.S., WILDE S MAGNETO-MACHINE. 25 copper wire, one end being soldered to the disc i, the other connected to the copper wire passing through but insulated from it by an ivory ring. By means of the wheel and spindle each pole of the armature is brought in rapid succession opposite each pole of the magnet, and that, as near as possible, without touching. The two armatures differ from one another ; the one termed the quantity armature is constructed of stout iron, and covered with thick insulated wire ; the other, termed the intensity armature, is constructed of slighter iron, and covered with from 1,000 to 2,000 yards, according to the size of the instru- ment, of fine insulated wire. The illustration exhibits the machine with its quantity armature." In the year 1847, the author's brother, Mr. Charles Watt, Chemist to the Australian Government, had such a machine constructed by the late Mr. Henley, in which the driving-wheel, with spindle attached, was fixed beneath the table, and the rotary motion given by means of a treadle, as in an ordinary lathe. Considering the early period at which it was made, the machine gave very satisfactory results in electro -chemical experiments upon a moderate scale, but for any really practical purpose it was quite unsuitable. Woolrich's Magneto-electric Machine. The first practical application of magneto -electricity to the electro -deposition of metals was made by Mr. J. S. "Woolrich, who, on August 1st, 1842, obtained a patent for a magneto -electric machine which was adopted in several large electro -plating establishments the first of these machines having been adopted, we believe, by Messrs. Prime and Son, of Birmingham, and which those gentlemen, a few years since, exhibited to the author as a disused relic, the functions of which had been transferred to a more effective contrivance. "We lately recognised this machine, which had long done duty for this firm as a substitute for voltaic batteries, at an establishment in London. Wilde's Magneto-electric Machine. This important machine, for which Mr. Henry Wilde obtained a patent in the year 1865, has proved of immense service to those who required to deposit large quantities of silver and other metals from their solutions. The machines have also been largely used at the copper works of Messrs. Elkington and Co., at Pembrey, near Swansea, for refining copper from crude slabs of the unrefined metal. For a long time after its introduction the Wilde machine remained without a competitor, and was the means of greatly extending the usefulness of the art of electro - deposition, more especially in the towns of Sheffield and Birmingham, where they have been very extensively employed. We may state, however, that the original form of machine has since been considerably improved, and we are enabled, through the courtesy of the Electric Engineering Company, of Manchester, successors to Messrs. H. Wilde 26 MAGNETO-ELECTRICITY. and Co., to furnish the following particulars of the new machines, which will doubtless prove interesting to those who deposit metals by electrolysis upon a large scale. Fig. 26 represents a 3 2 -magnet machine embodying Mr. "Wilde's latest improvements. This machine is capable of depositing, in a series of 130 vats, each having 40 square feet of positive and the same nega- tive surface, an aggregate weight of over 900 pounds of copper per Fig. 26. Wilde's Magneto-electric Machine. day of 24 hours, with an expenditure of 13 horse -power. The same firm manufacture a 12 -magnet machine of the same type as the fore- going, for the purposes of electro -plating, which has been adopted by many firms in Sheffield and Birmingham. This machine deposits about 30 ounces of silver per hour, with an expenditure of ^ to 2 horse- power. The action of these machines is thus described by the Electric Engineering Company in a communication to the author: "These machines (unlike the earlier ones of Mr. Wilde's invention, which GKAMME S MAGNETO-MACHINE. 2 7 are excited by a separate machine), are self -exciting, but at the same time are double -circuit machines ; that is, while the current from one or two of the coils in the revolving armature disc is used for exciting the series of electro -magnets, the current from the remainder of the coils is used for external work. This arrangement is free from the objectionable feature, common to single -circuit machines, of revers- ing the current whenever the speed is from any cause reduced below the usual amount, as the current from the polarised electrodes in the depositing vats is then at liberty to return, and reverse the magnetism of the machine while the speed is reduced, and is often a source of much inconvenience and loss to the electro -plater." We are in a position to corroborate this statement, having frequently known dynamo-machines, otherwise exceedingly effective and regular in their action, which have suddenly reversed while the bath was full of work, causing the whole of the deposited coating to disappear, and necessitating the recleaning of the articles. This untoward event has usually occurred in establishments which derived their steam-power from adjacent premises, the regularity of which could not be depended upon, owing to the variety of purposes to which the power was applied outside the plating works. It is within our own knowledge that many nickel-platers, who had adopted dynamo -electric machines in substitution for voltaic batteries, suffered much inconvenience from the irregularity of hired steam-power, and in not a few instances they have wisely purchased a gas-engine, with incalculable advantage to their daily work, and far greater economy. We understand that the Wilde machines have been successfully adopted by electrotypers, in which field there will doubtless be great extension of usefulness when our large printing firms recognise the full importance of the American system of substituting electro - typing for stereotyping, over which it has advantages which cannot long remain open to doubt. These machines are also extensively used in producing copper rollers for calico printing. Gramme's Magneto-electric Machine. This machine, which has attained a high rank as an electric -light machine, has not been much adopted in this country for the purposes of electro -deposition. It is, however, extensively applied on the Continent for these purposes, and notably at the electro -plating works of MM. Cristofle, in Paris. We lately observed one of these machines at work at the well-known establishment of the Nickel-plating Company, Greek Street, Soho, London, where it is employed in nickel-plating, and in depositing copper upon steel shot for the Nordenfelt gun. The author's friend and former pupil, Mr. Charles Blaker, chemist to the above firm, expresses himself much pleased with his Gramme, which appears to do excellent work, and to give no trouble whatever. 2 8 MAGNETO-ELE CTRICITY. The Gramme machine, Fig. 27, consists essentially of a ring of soft iron, covered with a large number of coils of insulated copper wire, the respective ends of which are connected with the separate sections of two commutators fixed upon the axis of the machine. This ring, with its coils and commutators fixed upon its axis, revolves between the poles of an electro-magnet. The capabilities of the machine are thus described : Fig. 27. Gramme's Magneto-electric Machine. " To deposit 600 grammes of silver requires one horse -power, and a speed of 300 turns per minute ; the tension (electromotive force) of the current being equal to that of two of Bunsen's cells, and its quantity equal to thirty-two such cells of ordinary size. At a speed of 275 revolutions per minute it has deposited 525 grammes of silver per hour ; at 300 turns, 605 grammes ; and at 325 turns, 675 grammes.* * When worked at so high a speed, the machine is liable to become heated and its effectiveness thereby considerably impaired. DYNAMO-ELECTRICITY. 2 9 The weight of the copper wire on the fixed electro -magnets was 135, and on the movable ones 40 kilogrammes.* The present form of the machine, as used for electro - deposition, is composed as follows : t Total weight 117-5 kilogrammes. Copper coils 47 o Total height '6 metre. Total width -55 Deposits silver per hour 6oo 4 grammes. Required power to work it 50' kilogramrnetres. Dynamo-Electricity. After the introduction of Wilde's Magneto- electric Machine in 1 866, and its subsequent exhibition before the Royal Society, where its capabilities were fully demonstrated, the late Sir Charles Wheatstone and Dr. Werner Siemens, experimenting quite independently of each other, produced, almost simultaneously, two machines, which were identical in principle, and involved a new feature in magneto -electricity the conversion of dynamic or mechanical force into electric force without the aid of permanent magnetism. The principle of this machine was explained by the late Sir C. W. Siemens, in a paper submitted to the Royal Society in February, 1867,]; from which we extract the following : " Since the great discovery of magnetic electricity by Faraday, in 1830, electricians have had recourse to mechanical force for the production of their most powerful effects ; but the power of the magneto -electric machine seems to depend in an equal measure upon the force expended on the one hand, and upon permanent magnetism on the other. An experiment, how- ever, has been lately suggested to me by my brother, Dr. Werner Siemens, of Berlin, which proves that permanent magnetism is not requisite in order to convert mechanical into electrical force ; and the result obtained by this experiment is remarkable, not only because it demonstrates this hitherto unrecognised fact, but also because it pro- vides a simple means of producing very powerful electrical effects. The apparatus employed in this experiment is an electro -magnetic machine, consisting of one or more horse-shoes of soft iron, surrounded with insu- lated wire in the usual manner of a rotating keeper [armature] of soft iron, surrounded also with an insulated wire, and of a commutator con- necting the respective coils in the manner of a magneto - electric machine . If a galvanic battery were connected with this arrangement, rotation of the keeper in a given direction would ensue. If the battery were * Telegraphic Journal, vol. i. p. 54. t Ibid., vol. iii. p. 198. I Proceedings of the Royal Society, vol. xv. p. 397 30 DYNAMO-ELECTRICITY. excluded from the circuit, and rotation imparted to the keeper in the opposite direction to that resulting- from the galvanic current, there would be no electrical effect produced, supposing the electro -magnet were absolutely free of magnetism ; but by inserting a battery of a single cell in the circuit, a certain magnetic condition would be set up, causing similar electro -magnetic poles to be forcibly approached to each other, and dissimilar poles to be severed, alternatively, the rotation being contrary in direction to that which would be produced by the exciting current. "Each forcible approach of similar poles must augment the mag- netic tension and increase, consequently, the power of the circulating current ; the resistance of the keeper to the rotation must also increase at every step until it reaches a maximum, imposed by the available force and the conductivity of the wires employed. The co-operation of the battery is only necessary for a moment of time after the rotation has commenced, in order to introduce the magnetic action, which will thereupon continue to accumulate without its aid. With the rotation the current ceases ; and if, upon restarting the machine, the battery is connected with the circuit for a moment of time with its poles reversed, then the direction of the continuous current produced by the machine will also be the reverse of what it was before. Instead of employing a battery to commence the accumulative action of the ma'chine, it suffices to touch the soft iron bars employed with a permanent magnet, or dip the former into a position parallel to the magnetic axis of the earth, in order to produce the same phenomenon as before. Practically it is not even necessary to give any external impulse upon restarting the machine, the residuary magnetism of the electro -magnetic arrangements employed being found sufficient for that purpose."* The principle of the dynamo -electric machine is thus further described by Dr. Siemens: "Induced currents are directed through the coils of the electro -magnets which produce them, in- creasing their magnetic intensity, which in its turn strengthens the induced currents, and so on, accumulating by mutual action until a limit is reached. . . . The name dynamo- electric machine is given to it because the electric current is not induced by a permanent mag- net, but is accumulated by the mutual action of electro -magnets and a revolving wire cylinder or armature. It is found that as the dynamic force required to drive the machine increases, so also does the electric current ; it is, therefore, called a dynamo- electric machine." Siemens' Dynamo-electric Machine. This remarkably effective * In wrought iron there is always some residual magnetism ; there is, therefore, no necessity to start the magnetism with a permanent magnet. Dr. Siemens. SIEMENS DYNAMO-MACHINE. 3 1 apparatus (Fig. 28), which, in its application to electric lighting has attained the highest rank, and from its great power, uniform action, and reliability has done much to establish the practicability and use- fulness of electric lighting, is also manufactured by Messrs. Siemens Brothers, at their extensive works at Charlton Pier, Woolwich, specially for the purposes of electro -deposition and the refining Fig. 28. Siemens' Dynamo-electric Machine. of copper by electrolysis. One of these machines, suitable for electro- typing, works up to 4 baths arranged in series, and deposits in each cell up to 7 ozs. of copper per hour, the cathode surface of each cell being 21 square feet. The electromotive force is equal to 3 to 6 Daniell batteries, and the power absorbed i J horse-power. A machine suitable for silver-plating, coppering iron, &c., works through a 32 DYNAMO-ELECTKICITY. single bath or more, placed parallel, and deposits 1 1 ozs. of silver per hour, with an absorption of ^ to I horse-power. A third type, suit- able for nickeling, brassing, &c., deposits if ozs. of nickel per hour, producing " a good deposit of nickel in three minutes over a surface of 10 square feet. Difference of potential at the terminals, 6 to 12 Daniells; absorption of horse -power to I." The larger type of these machines, " C 12," is constructed for the purposes of refining copper from the crude metal, and is capable of depositing 5 cwt. of copper per twenty-four hours, with 7^ horse-power, provided the anodes do not contain more than 4 per cent, impurities. For this machine forty baths are required. Western's Dynamo-electric Machine. The introduction of this clever machine from the United States, in 1874, by Mr. A. Van Fig. 29. Western's Dynamo-electric Machine. Winkle, of the firm of Condit, Hanson, and Van Winkle, gave an ex- traordinary impetus to the nickel-plating industry throughout the whole country. Being of small dimensions, of compact form, and yielding an abundant current, it became readily adopted by a large number of firms. It was at the author's suggestion and recommenda- tion that the first of these machines was tried and adopted by the Plating Company, Limited, of Kirby Street, London, in that year, and though he had some difficulty in overcoming the prejudices of the foreman of that establishment, by insisting upon a fair trial being given GULCHER DYNAMO- ELECTRIC MACHINE. 33 and taking care that no obstacle should be thrown in the way, he suc- ceeded in securing not only a fair trial of its capabilities, but its ready adoption by the company. The Weston machine was subsequently adopted by a great number of firms, amongst which were many that would probably never have embarked in nickel-plating but for the facil- ity which this machine offered in generating the requisite electric cur- rent at the cost of less than one horse-power. There can be no doubt whatever that the remarkable development of nickel-plating in this country and in America, as also the substitution of electro typing for the stereotype process in American printing establishments, are greatly, if not chiefly, due to the introduction of the "Weston dynamo -electric machine. Quicker Dynamo -Electric Machine. This machine, which is manufactured by the Gulcher Electric Light Company, at Battersea, is specially constructed to suit the requirements of electro -metallurgists and electro-platers, and has been successfully adopted, at Swansea, by Messrs. Vivian, and Messrs. Lambert and Co., for the electrolytic refining of copper. The machine has also been adopted by Mr. W. H. Hills, of Chester, for the same purpose, and by Mr. Bown, of Birmingham and others for nickel-plating. Several large firms are also using this machine for electro -pickling sheet-iron plates previous to tinning them. These machines work at low speed, and have ample bearing surfaces, so that while steadiness and regularity of current are insured, with absence of sparking, the wear and tear are greatly reduced. Having used one of the improved Gulcher machines during a period of many months, we may say that it enabled us to carry out a long series of practical trials with perfect ease and certainty, and in no instance did it fail to yield what was required a perfectly steady and regular current. The following description explaining the construction of the Gulcher machine has been forwarded at our request by Mr. W. C. Mountain, the manager of the Gulcher Works : This dynamo may be described as of the Paccinoti type, i.e. the armature of the machine is in the form of a fly-wheel, and the copper conductors in which the current is induced are wound on the rim at right angles to the circumference. This armature, when finished, is mounted upon a steel spindle, and revolves between electro -magnets having alternate north and south polarity grouped round its circum- ference. The engraving, Fig. 30, represents a Gulcher dynamo with four poles, that is, two north and two south. It has been recently found, in making the ordinary sizes of this dynamo, that it is not advisable to increase the number of the poles beyond four or six, the most economical plan being to make the magnets heavy, that is, large in section, on account of the increased efficiency thus obtained, D 34 DYNAMO-ELECTRICITY. GULCHER DYNAMO-ELECTRIC MACHINE. 35 Upon examination of the woodcut it will be noticed that as the arma- ture revolves in the bearings it passes between the pole-shoes grouped round the circumference, the result being that lines of magnetic force, which may be said to sprout out from the magnets, are cut at right angles by the armature coils, which sets up an E.M.F. and current. The current from the armature then passes by connecting- wires to the commutator, which is placed between the outside bearing and the frame of the machine. The commutator is composed of a number of wedge-shaped copper bars, cramped together by a gun-metal sleeve, each section being carefully insulated with mica ; the number of sec- tions corresponds with those on the armature, and varies from sixty to one hundred and eighty, according to the size of the dynamo. On the end bearing a revolving strap is fixed carrying two spindles, upon which the collecting brushes are placed. The strap is made so that it will revolve backwards or forwards, in order that the brushes may be placed in any desired position upon the commutator. The brush-holders are made of gun-metal, and are never less than two, and sometimes as many as six in number, according to the output of the dynamo. These are arranged with a throw-off catch and tension- adjusting screw, so that the brushes may be thrown back, and held off the commutator when desired ; or the tension of the brush upon the surface of the commutator can be accurately adjusted. Flexible connecting-cables are attached to each brush-holder, and led to ter- minals on each side of the machine, from which points the current generated by the dynamo passes by main cables to the depositing or plating tanks, or to the arc and incandescent lamps, according to the purpose for which the dynamo is required. The magnets used in these machines are constructed of the softest wrought iron obtainable, which is carefully annealed before using ; the inside ends of the mag- nets are connected by a cast-iron pole-shoe ; the outside ends of the bars are turned down slightly, and are secured by nuts into the two cast-iron circular frames of the machine ; this method of construction gives ample magnetic contact. The magnet coils are wound on loose bobbins made of charcoal iron, the object being to enable the coils to be taken off and readily replaced in case of accident. The armature hub, which is in the form of a pulley, is made of the finest quality of phosphor bronze, and the run wound up with char- coal-iron wire of rectangular section ; when finished it has the form of a fly-wheel. This construction of the armature totally avoids all heating, and consequent loss of efficiency. Special attention is also paid to the construction of the bearings, a point of vital importance in any class of machinery constructed to run at high speeds for a lengthened period. The cast-iron brackets or pedestals are bolted to the bedplate of the machine, each bracket being fitted with a cast-iron DYNAMO-ELECTRICITY. Fig. 31. cap, which affords means of adjustment. The bed for the phos- phor bronze bearing is then carefully bored and faced to a stan- dard size and length, and bushes of the same material, which are also of standard sizes, and in halves, are fitted. The side frames of the machine are made in halves, and secured by four turned bolts, so that by simply removing them, and taking off the bearing caps, the top of the machine can be lifted off, and the armature and spindle lifted out of the dynamo. The Giilcher Company also manufacture a 2 -pole vertical type dynamo, specially for electro-plating purposes. This machine, which is shown in Fig. 3 1 , is made in four sizes, and from the moderate prices charged, from 25 to 40, are well suited for small plating works. The smallest of these machines is constructed to give a current of 100 amperes, and the larger machine 300 amperes, with an E M.F. of 5 volts. The speed required is about 1,500 revolutions. We recently saw some of these machines in course of construction, and were much pleased with the evident care that was bestowed upon them. Crompton's Dynamo -Electric Machine. This machine (Fig. 32), which is manufactured by Messrs. R. E. Crompton & Co., of Chelmsford and London, has been extensively adopted for electric lighting, both for public and private use, and has also been applied to the refining of copper by electrolysis, several of the machines having been supplied to Messrs. Vivian & Sons, and Messrs. "Williams; Foster & Co., of Swansea. The special advantages claimed for the Crompton dynamo have been described to us as follows : The machines have a very strong magnetic field ; the armature, which in large machines has to stand so severe a strain, is a thoroughly good mechanical job, as the core is carried on radial bars made of the hardest and toughest aluminium bronze, fitted to the spindle by a dove-tailed joint, so that the whole of the twisting strains are trans- mitted direct from the spindle to the winding, and thus many of the old breakdowns arising from the slipping of the core, or the rising of the core, are entirely done away with. The efficiency of these machines is remarkably high, 94 per cent, appearing as useful electrical power at the terminals of the dynamo. The machines for electro -deposition are in three standard sizes, namely : 50 volts, 500 amperes ; 50 volts, 750 amperes ; and 50 volts, rooo amperes : the horse-power required CROMPTON S DYNAMO-ELECTRIC MACHINE. 37 being respectively 35^, 53, and 71. The same firm have recently constructed the largest dynamo in the world for the Cowles Electric Fig. 32. Crompton's Dynamo-electric Machine. Smelting Furnaces at Stoke-on-Trent, to which reference is made in another part of this work. Scliuckert's Dynamo -electric Machine. This machine, which is extensively used in Germany, is said to be very successful, more especially in its larger types. We have, however, seen one of the smaller machines employed for electrotyping, at Messrs. Cassell and Co.'s, Ludgate Hill, London, which we were informed gave perfect satisfaction. Whilst almost noiseless in action, it presented the ap- pearance of being an exceedingly well -constructed machine. "We understand that the more closely the maker follows the original 38 DYNAMO-ELECTRICITY. design of the inventor, the greater is the practical value of the machines. The larger type of this dynamo is shown in Fig. 33. By winding the bobbin and the coils of the electro-magnets with a finer wire, the number of volts may be increased two, three, or fourfold, without altering the power or the speed of the machine. 33- Schuckert's Dynamo-electric Machine. Mather's Dynamo -electric Machine. This is an American machine, designed by Mr. Mather, of New York, in which the Siemens armature plays an important part. It is said to be a very strongly constructed machine, and well combined as regards the magnetism and the access of the brushes. One type of this machine, which runs at a speed of 800 revolutions per minute, is said to deposit 10 kilogrammes of copper at an expenditure of 7 horse -power. CHAPTER III. THERMO-ELECTRICITY. Seebeck's Discovery of Thermo-Electricity. Thermo-electric Laws. Ther- mo-electric Piles and Batteries. C. Watt's Thermo-electric Battery. Becquerel's Thermo-Pile. Clamond's Thermo-electric Pile. Wray's Thermo-Pile. Noe's Thermo-Battery. The Future of Thermo-Elec- tricity. Seebeck's Discovery of Thermo-Electricity. In the year 1821 Professor Seebeck, of Berlin, made the remarkable discovery that when a bar of antimony, a, Fig. 34, with a piece of brass wire coiled round it, i, and attached to the other end in the form of a loop, c, was heated by the flame of a spirit lamp at b, where the two metals were in contact, that this caused the deflection of a magnetic needle placed at d. The discovery established the fact that electricity could be generated by the action of heat upon two different metals. A more effective arrangement for producing a current in this way is obtained Fig. 34- Fig. 35- by means of antimony and bismuth united, as in Fig. 35, so as to form a hollow parallelogram, A representing the bar of antimony, and B, a bar of bismuth ; on applying heat to one of the junctions, by a spirit lamp, a quantitative current of electricity is put in motion through the metals, which is immediately indicated by the deflection of a magnetic needle, and this effect is considerably increased if the opposite junction of the metallic bars be at the same time cooled, by the application of ice, or a freezing, mixture (or blotting-paper saturated with ether). It is not necessary, however, that two metals should be employed to produce the above result, for although a platinum wire, connected to a galvanometer, and heated, produces no 4O THERMO-ELECTRICITY. effect upon the needle, if it be knotted or twisted a deflection is noticed, showing, when heat is applied on the right of the knot, that the direction of the current is towards the left ; this effect is ascribed to the unequal rate at which the heat travels on the two sides of the obstruction ; and again, if the wire be divided, one end of it being cooled, and the other heated, the needle will deviate when the metals are brought into contact, indicating a current from the hot to the cool surface. If a bar of bismuth be soldered to one end of the galvanometer wire, and a bar of antimony to the other, no effect is produced on bringing the two bars into contact when they are both of the same temperature ; but if one of them be either heated or cooled, and then made to touch the other, the flowing of an electric current is immediately indicated. Brande. Sir William Thomson proved, in 1856, that if portions of a metallic wire be stretched by weights, and connected with other portions of the same wire not so stretched, that, on applying heat to their junctions, a current is determined from the stretched to the unstretched wire through the heated point. All metals, as also some other bodies, are capable of yielding thermo- electric currents, and it has been shown that this property has no connection with their voltaic relations to each other or with their con- ductibility, either as regards heat or electricity. In arranging a thermo-electric series, the greatest effects are obtained when the most positive is connected with the most negative metal. . When any two metals in the subjoined series are heated at their point of junction, electricity is developed in such a manner that each metal becomes positive to all below, and negative to all above it in the list, the reverse order being observed when the point of junction is cooled : THFRMO-ELECTfilC SERIES. Galena. Bismuth. Mercury) Nickel 3 Platinum. Palladium. Cobalt | Manganese/ Tin. Lead. Brass. Rhodium. Gold. Copper. Silver. Zinc. Cadmium. Charcoal. Plumbago. Iron. Arsenic. Antimony. Dr. Matthiessen arranged the following order and electric energy of various bodies for temperatures usually ranging between about 40 and 100. In the table the electromotive force of the thermo- current THERMO-ELECTRIC LAWS. 4! excited between silver arid copper is taken as equal to i , the current passing from the silver to the copper at the heated end. The numbers represent the force of the current between silver and each metal in succession, heated at the same point. Where the positive sign -|- is prefixed the current is from the silver to the other metal at the point of junction ; and where the negative sign is prefixed, the current is from the other metal at the heated point towards the silver. The asterisks signify that the metal specified is supposed to be chemically pure. THERMO-ELECTRIC ORDER OF METALS. 'j 13-670 Bismuth, commercial pressed wire. 35-81 *Bismuth, pressed wire . . 32*91 *Bismuth, cast 24-96 Crystallised Bismuth, axial 24-59 Crystal of Bismuth, equato- rial I 7' I 7 Cobalt 8-97 Potassium 5*49 Nickel . 5-02 Palladium 3-56 Sodium 3'94 ^Mercury 2*524 Aluminium 1*283 Magnesium ^-'^75 *Lead, pressed wire . . . 1*029 *Tin, pressed wire .... rooo Copper wire rooo Platinum 0-723 Iridium 0-163 * Antimony, pressed wire . . 0-036 *Silver o-ooo Thermo-electric Laws. According to Becquerel, the following laws govern the development of electricity in thermo-electric pairs: 1. In a thermo-electric couple, so long as the difference in tempera- ture between the two junctions remains the same, the current is rigorously constant. 2. In a thermo-electric pile the intensity of the current, all else being equal, is proportional to the number of couples. 3. The intensity of thermo-electric currents increases with the difference of temperature between the junctions ; and if one be at zero, this intensity is proportional, within the limit of 40 to 45, to Gas coke, hard '57 *Zinc, pressed wire .... 0-208 *Copper, voltaic * .... 0*244 ^Cadmium 0*332 Antimony, pressed wire . . 1-897 Strontium 2-028 Lithium 3'?68 *Arsenic 3-828 Calcium 5-260 Iron, piano wire 5*218 Antimony, axial 6-965 Antimony, equatorial . . . 9*435 *Red Phosphorus .... 9 600 * Antimony, cast 9*871 Alloy, 12 bismuth i tin, cast Alloy, 2 antimony . ) i zinc, cast . . .} 22 ' 7 ^Tellurium 179-80 ^Selenium 290-0 Electrolytic Copper. 42 THERMO-ELECTRICITY. the temperature of the other junction. In this law the limit of 45 is applicable to a copper-antimony couple, but it varies with the metals. For iron and copper it extends as far as 300, and as much above that for iron and palladium. Thermo-electric Files and Batteries. Since Seebeck's dis- covery was made known, many attempts have been made to design thermo-electric apparatus capable of being utilised as an economical source of electric power. The arguments adopted, when the first efforts were made in this direction, some forty years ago, when elec- tricity, for practical purposes, was chiefly derived from voltaic batteries, was this : " There will be no consumption of zinc, acids, and mercury ; no attention necessary after the thermo-battery is once set in action ; only moderate heat required to excite electric action in the metals ; so we shall get our electricity for next thing to nothing." That was the impression in the minds of many at the time we refer to, and it will certainly not astonish us if at some future period thermo- electricity realises the hopes and aspirations then expressed. The splendid results obtained by means of magneto and dynamo -electric machines may have diverted the attention of electricians from a closer study of thermo-electricity than we believe the subject demands, but we are inclined to think that at no distant date the conversion of heat into electric energy will receive more attention than has hitherto been accorded to it. The first practical application of Seebeck's discovery was made by Moses Poole, who, in 1843, obtained a patent for the use of a thermo- pile, which, however, did not meet with much success. Many sub- sequent efforts were made to bring thermo-electricity into practical use, amongst which may be mentioned a thermo-electric battery devised by the author's brother, Mr. Charles Watt, in 1851, and re- constructed by the author two years later. This battery was originally designed to consist of two thousand pairs of bismuth and antimony plates, but a difficulty arose in its construction owing to the very fragile nature of the metals, when combined in an extended series. Each pair of plates having to be united by pewter solder, it was found to be exceedingly difficult to complete even a single row of couples without an accidental fracture, or fusion of the bismuth while soldering the junctions, and after many futile attempts the construction of the battery had to be abandoned. In 1853, however, the author determined to make an attempt to reconstruct the battery, which he succeeded in doing, unaided, in about six or eight weeks. This thermo-battery was constructed as follows : C. Watt's Thermo-electric Battery. The elements employed were bismuth and antimony, and the plates were of the form shown in Fig. 36, being about 3 inches in length, and about one-eighth of WATT S THERMO-ELECTRIC BATTERY. 43 an inch in thickness, the different metals "being cast in moulds of uniform size and form. Fig. 37 represents a single pair of elements united by solder at their lower extremity, a being the antimony and b the bismuth plate. Two conducting wires (P and N) indicate the poles or electrodes. To construct the battery in such a way that it would not be liable to injury, even from trifling accidental causes, was by no means an easy task ; the solder employed, owing to the ready fusibility of bismuth as compared with antimony, was the most " easy running" solder that could be procured, and if great care were not exercised in heating and applying the soldering iron, the bismuth, uniting with the solder and forming fusible metal, would run, or melt, before the solder could be made to attach itself to the antimony. To prevent these mishaps^ which had been greatly the cause of failure in constructing the battery originally, it was deter- mined in the first instance to " tin," that is spread, the solder upon those edges of each of the antimony plates which were to be united to the bismuth, and, by so doing, a very delicate application of the soldering-iron, well supplied with the molten alloy, soon united the metals at their extremities with little or no acci- dental melting of the bismuth. In fact, the soldering-iron was simply drawn along the points of junction with a steady Fig- 36- and uniform sweep, by which the respec- Fig. 37. tive couples were securely and perfectly united with little or no accident when the hand had become accus- tomed to the manipulation. It may be mentioned as a fact that many different workmen had endeavoured to solder the bismuth and antimony couples, but had been compelled to give up the task as hopeless owing to the frequent melting of the bismuth when the soldering-iron was applied, and the snapping of the fragile plates when but a few of them were united. In order to prevent the breaking of the plates by their own weight when a large number were united in a series, a bar of well- seasoned beech, smoothly planed on all sides, and nearly two inches in thickness, being perforated at the ends to receive screw bolts, was laid across a trestle ; one or two pairs of the metals were then laid edge- wise across the bar, with their projecting surfaces overlapping the two vertical surfaces of the wooden bar ; a second wooden bar was then placed over the couples in the same way, a half-inch wooden wedge being placed between the two bars, at the opposite end, cor- responding with the narrower parts of the plates, the two ends of the bars nearest the plates were then securely tied together, and those at the opposite end temporarily fastened in the same way. Being thus secured, the soldering-iron was applied first to the lower end of the first 44 THEBMO-ELECTKICITY. couple, then to the upper ends of the second and third plate, and next to the lower end of the second couple ; these being secured, other couples were introduced by carefully untying the cord at the opposite end of the wooden bars, removing the wedge, and passing the pairs of metals between the wooden bars until the whole series were intro- duced. The cord was again applied and made rigidly secure, and the soldering-iron again applied until the entire series of couples had been soldered on one side ; when this was effected the bars were turned over and the bottom surfaces of each couple carefully soldered ; by shifting the position of the wooden bars the three angles of each pair, alternately top and bottom, were united by soldering until the whole row or series of plates had been connected. The ends of the wooden bars were next made secure by means of screwed bolts, when the Fig. 38. C. Watt's Thermo-electric Battery. arrangement of the first series was complete. The end plates of each series were, respectively, bismuth and antimony. Five such groups were constructed, and these were afterwards formed into a compound battery in the following way : A wrought-iron chamber A, Fig. 38, fitted with a pipe b, was fur- nished with an inner flange at each end, upon which the bars carry- ing the soldered couples rested ; each row of plates was connected at its positive end with the negative plate of the next row by a bent wire, as in the engraving, and the terminal wires N and p then con- nected by soldering. The chamber was supplied with oil to the depth of about three inches, heated, when the battery was required for use, by means of gas jets from a perforated pipe placed beneath the chamber. The upper surfaces of the plates were cooled by means of CLAMOND'S THERMOPILE. 45 a four-winged fan (c) of simple construction, set in motion by a pulley (fl) connected by a strap to a revolving shaft above. This fan, the frame-work of which was of wood, was covered with calico coated with a thin mixture of size and whiting. When the fan was in motion the cold produced was considerable, and, by carefully regu- lating the heat of the oil in the chamber beneath, an uniform action of heat and cold on the opposite surfaces of the couples could be readily maintained. Becquerel's Thermo-File. As far back as 1827 M. Becquerel, sen. , had noticed that a copper wire, coupled with a wire of the same metal sulphuretted on its surface, formed, by raising the temperature of one of the junctions from 200 to 300, a thermo-electric couple more energetic than could be obtained with other metals. In 1865 M. Ed. Becquerel conducted a series of experiments to determine the thermo-electric power of artificial sulphuret of copper, and found that this substance, heated to 200 or 300, was strongly positive, and that a couple composed of this sulphuret and copper had an electro- motive force nearly ten times greater than that of a bismuth -copper couple. Native sulphuret of copper, on the contrary, is highly negative. The melting point of the artificial sulphuret being about 1,035 this substance may be employed at very high temperatures. In constructing a thermo-pile with this sulphuret it is united to an alloy composed of copper 90, nickel 10 parts. Clamond's Thermo-electric Pile. This thermo-pile, which has been much adopted on the continent, and has also been used to some extent by electro -plating firms in Birmingham and Sheffield, though with variable success, owing, probably, to the conventional distaste which some English workmen have for recognising merit or advantage in anything novel. Since Clamond's pile, regardless of all prejudice, has been proved to be an exceedingly effective generator of thermo- electricity, the following description of the contrivance, by Mr. Latimer Clark, will be read with interest* : 11 The mixture employed by Clamond consists of an alloy of 2 parts antimony and I of zinc for the negative metal, and for the positive element he employs ordinary tinned sheet-iron, the current flowing through the hot junction from the iron to the alloy. The combina- tion is one of great power. Each element consists of a flat bar of the alloy from 2 inches to 2| inches in length, and from f to I inch in thickness. Their form is shown in Fig. 39, by which it will be seen that, looking at the plan, they are spindle-shaped or broader in the middle than at the ends. The sheet -tin is stamped out in the form shown in Fig. 40 ; the narrow portion is then bent in the forms * Journal of the Society of Telegraph Engineers, vol. v. p. 321. 4 6 THERMO-ELECTRICITY. shown, in which state they are ready for being fixed in the mould. The melted alloy is poured in, and, before it has cooled, the mould is opened and the bars removed with the lugs securely cast into them. The mould is heated nearly to the melting point of the alloy, and 10 or 12 bars are cast at one time. A little zinc is added from time to time to make up for the loss due to volatilisation. The alloy melts at about 500 Fahr. ; it expands considerably on cooling. The more frequently the alloy is recast the more perfect becomes the mixture, so that old piles can be reconverted with advantage and with little loss beyond that of the labour. The alloy is extremely weak and brittle and easily broken by a blow in fact, is scarcely stronger than loaf sugar. " The tin lugs are bent into form, and the bars are arranged in a radial manner round a temporary brass cylinder, as shown in Fig. 39, a thin slip of mica being inserted between the tin lug and the alloy, to prevent contact, except at the junction. The number of radia Fig. 39- Fig. 40. bars varies with the size of the pile, but for the usual sizes eight or ten are employed. As fast as the bars are laid in position, they are secured by a paste or cement formed of powdered asbestos and soluble glass, or solution of silicate of potassa ; flat rings are also formed of the same composition, which possesses considerable tenacity when dry ; and as soon as one circle of bars is completed, a ring of the dry asbestos cement is placed upon it, and another circle of elements is built upon this, and so on until the whole battery is formed. Cast-iron frames are then placed at top and bottom of the pile, and drawn together by screws and rods, so as to consolidate the whole, and in this condition the pile is allowed to dry and harden. Looked at from the inside, the faces of the elements form a perfect cylinder, within which the gas is burned. The inner face of each element is protected from excessive heat by a tin strip or cap of tin bent round it, before it is imbedded in the cement , the projecting strips of tin from the opposite ends of each pair of elements are brought together and soldered with a blowpipe and soft solder. The respective rings are similarly connected, and the CLAMOND'S THERMO-PILE. 47 whole pile is complete, except as regards the heating arrangements. The positive pole of these piles is always placed at the top. Gumming was the first to use this stellar arrangement of couples. The pile is usually heated by gas mingled with air, on the Bunsen principle ; gas is introduced at the bottom of a tube of earthenware, which is closed at the top, and is pierced with a number of small holes throughout its length, corresponding, approximately, in number and position with the number of elements employed. Before entering this tube, the gas Fig. 41. Section of Clamond's Thermo-pile. is allowed to mix with a regulated proportion of air, by an orifice in the supply tube, the size of which can be adjusted ; the mixed gases escape through the hole in the earthenware tube, and there burn in small blue jets, the annular space between the gas tube and the ele- ments forming a chimney to which air is admitted at bottom, the products of combustion escaping at the top. In order to prevent injury from over -heating, and to diminish the consumption of gas, 48 THERMO-ELECTRICITY. M. Clamond has introduced a new form of combustion chamber, by which he obtains very great advantages. This form is shown in Fig. 41. The mixture of air and gas is burnt in a perforated earthen- ware tube, as before described, but instead of extending the whole height of the battery, it only extends to about one -half of its height. The earthenware tube is surrounded by an iron tube of larger diameter, which extends nearly to the top of the battery, and is open at the top. Outside this iron tube, and at some distance from it, are arranged the elements in the usual manner. A movable cover fits closely over the top of the pile, and a chimney is connected to the bottom of the pile. Leading off from the annular space between the iron tube and the interior faces of the elements, the air enters at the bottom of the iron tube, and the heated gases, passing up the tube, curl over at the top, and descend on its outside, escaping eventually by the chimney. The elements are heated partly by radiation from the iron tube, and partly by the hot gases which pass outside the tube, downwards towards the chimney. By this arrangement, not only is great economy of gas effected, the consumption, as I am informed, being reduced by one -half ; but the great advantage is obtained that the jets of gas can never impinge directly on the elements, and it is thus scarcely possible to injure the connections by over-heating. In the event of a bad connection occurring, it is easy to find out the imperfect element, and throw it out of use by short-circuiting it over with a piece of wire, and the makers have no difficulty in cutting out a defective element and replacing it by a sound one. Coke and charcoal have also been employed as a source of heat, with very great economy and success ; in fact, there are many countries and places where gas would not be procurable, but where charcoal or coke could be readily obtained. The tension produced by Clamond's thermo- elements is such that each twenty elements may be taken as practically equal to one Daniell's cell, or about one volt." It is stated that a Clamond pile of 100 bars, with the consumption of 5 cubic feet of gas, deposits about I ounce of silver per hour, and the same machine, arranged in multiple arc (that is for quantity] will deposit about I ounce of copper in the same time ; 400 large bars, consuming 2 Ibs. of coke per hour, will deposit about four times the above quantities in the same period of time. Wray's Thermo -File. In this improvement, the bars are cast, as usual, under pressure, and a small tongue of tinned iron is cast down the centre of the bar, extending nearly its whole length, by which the strength is greatly increased, and it is also stated that it not only decreases the resistance, but also increases the electromotive force. The battery is built up by a number of discs made up of burnt clay, pipe clay, or biscuit ware, and between each disc a small triangle of NOB'S THERMO-ELECTRIC BATTERY. 49 the same material is interposed, with metal rods to hold the whole together, consequently these discs and triangles, when in place, sustain the whole pressure, and the thermo-bars rest upon them, and can be removed and rearranged when necessary ; by this arrange- ment they are not so liable to be injured by the heat of the gas. To prevent the gas flames from impinging directly upon the bars, or against the iron cylinder within the thermo-battery, an inner cylinder of earthenware is employed, which forms the centre of the battery, and the bars of metal are built up around the cylinder, and in close contact with it, each bar being bedded up against it with asbestos cement. The gas flame, therefore, cannot come in direct contact with the bars, consequently they are less liable to injury from heat, while the heat is also more uniformly distributed. The supply of air is regulated by small covers of fire-clay, consisting of perforated radial discs, placed on the top of the pile. Noe's Thermo-electric Battery. This machine, invented by M. Nb'e, of Vienna, consists of a series of small cylinders, about 1 5 inch in length, and |ths of an inch in diameter, composed of an alloy of thirty-six and a half parts of zinc and sixty-two and a half parts of antimony for the positive element, and stout German silver wire as the negative element. The junctions of the elements are heated by small gas jets, and the alternate junctions are cooled by the heat being conducted away by large blackened sheets of thin copper. It is stated that from nine to ten of th se couples have an electromotive force equal to one Daniell cell, and twenty pairs, with great external resistance, are equal to one Bunsen. "With small external resistance, twenty quadrupled Noe elements are somewhat stronger than one Bunsen. In another arrangement of this thermo- battery, the negative wire, fixed to the positive metal, is bent back from the point of contact, in an acute angle. A small metallic rod is fused to the two elements at the same point. Twenty elements are arranged in a circle, the metallic rods being in the centre. The space in the centre is covered with a plate of mica, and the metallic rods are then heated by means of a circular gas-flame. The electromotive force of twenty such elements is equal to 19-4, one Bunsen being equal to twenty. The resistance of each element equals '056. These machines have been used both in Vienna and Berlin for electroplating and electro typing. The Future of Thermo-Electricity. When we reflect that in the present advanced state of electrical science many difficulties which were formerly considered almost insurmountable have been overcome, and the imperfect efforts of our predecessors have been improved upon and brought into practical use, it may not be too much to say that we believe that thermo-electricity has a great future before it. $0 THERMO-ELECTRICITY, Indeed, the success of M. Clamond's exertions, as also those of his com- petitors which will doubtless be supplemented by still greater results hereafter are but evidences that thermo-electricity can be utilised for practical purposes, as a substitute not only for the voltaic current, but also, in a minor degree at present, for magneto and dynamo -electricity. When it is borne in mind that in the thenno-pile the current is obtained solely at the cost of so much heat, and that there is no exhaustion of the elements or wear and tear of its constituent parts, we may readily conceive that great exertions will yet be made to construct thermo -piles or batteries, capable of yielding currents of far greater power than has yet been obtained from this source. The thermo -pile is the only example of the direct conversion of heat into electric energy, and, ao far as is known, this is obtained without any other waste beyond that of the fuel consumed in generating the heat necessary to excite and keep in action the elements of which the pile is composed. CHAPTER IV. HISTORICAL REVIEW OF ELECTRO -DEPOSITION. Announcement of Jacobi's Discovery. Jordan's Process Published. Jordan's Process. Spencer's Paper on the Electrotype Process. Effect of Spencer's Paper. Vindication of Jordan's Claim. Mr. Dircks on Jordan's Discovery. Sir Henry Bessemer's Experiments. Dr. Golding Bird's Experiments. Origin of the Porous Cell. LONG before the art of Electro -deposition was founded upon a prac- tical basis, it was well known, experimentally, that several metals could be deposited from their solutions upon other metals, by simply immersing them in such solutions ; but this knowledge was of little importance beyond the interesting nature of the results obtained. The schoolboy had been accustomed to amuse himself by producing the ever-popular " lead tree," by suspending a piece of zinc attached to a copper- wire in a solution of sugar of lead, or the " silver tree," with a solution of nitrate of silver and mercury ; or he would coat the blade of his penknife with copper, by dipping it for a moment in a weak solution of sulphate of copper (bluestone). But these, and the like interesting facts, were of no practical value in the arts. It was also known that articles of steel could be gilt by simple immersion in a dilute solution of chloride of gold (that is gold dissolved in aqua regia), or still better, in an ethereal solution of the chloride, and this simple process was sometimes adopted in the ornamentation of engraved articles, in imitation of the process of damascening. The eyes of needles were also gilt by a similar process, and " golden- eyed needles" became popular amongst the fair sex. "With this exception, however, the deposition of metals, even by simple immersion in metallic solutions, was regarded as interesting and wonderful, but nothing more. As far back as about the year 1820, the author's father covered the " barrels " of quill pens with silver, by first steeping them in a solution of nitrate of silver, and afterwards reducing the metal to the metallic state in bottles charged with hydrogen gas, the object being to protect the quills from the softening influence of the ink. In the year 1836, Prof essor Daniell made known his constant battery, and in the same year, Mr. De la Rue constructed a modification of this battery, in working which he observed that " the copper-plate is also 52 HISTORICAL REVIEW OP ELECTRO-DEPOSITION. covered with a coating of metallic copper which is continually being deposited ; and so perfect is the sheet of copper thus formed, that, being stripped off, it has the counterpart of every scratch of the plate on which it is deposited.* Although this interesting observation did not lead to any direct application at the time, it is but reasonable to presume that in the minds of some persons the important fact which it disclosed would have suggested the possibility of its being suscep- tible of some practical application. It was not until the following year (1837), however, that the electro- deposition of metals, experi- mentally, seriously occupied the attention of persons devoted to research, the first of whom was Dr. Golding Bird, who decomposed solutions of the chlorides of ammonium, potassium, and sodium, and succeeded in depositing these metals upon a negative electrode of mercury, t whereby he obtained their amalgams. From the time when his interesting results became known, many persons repeated his experiments, while others turned their attention to electrolysis as a new subject of investigation, and pursued it with different objects, as will be shown hereafter. Mr. G. E. ElMngton, in 1836, obtained a patent for " Gilding cop- per, brass, and other metals " by immersing the articles in a boiling alkaline solution containing dissolved gold. This was followed, in 1837, by several other patents granted to Mr. H. Elkington for coat- ing metals with gold and platinum, and for gilding and silvering articles. In 1838,; Mr. G. R. Elkington, with Mr. O. W. Barratt, patented a process for coating articles of copper and brass with zinc, by means of an electric current generated by a piece of zinc attached to the articles by a wire, and immersing them in a boiling neutral solution of chloride of zinc. This was the first process in which a separate metal was employed in electro-deposition. Announcement of Jacob!' s Discovery. About the period at which the above processes were being developed, it appears that several other persons were engaged in experiments of an entirely different character and of far greater importance, as will be seen by the results which followed their labours. In St. Petersburg, Pro- fessor Jacobi had been experimenting in the deposition of copper upon engraved copper- plates, a notice of which appeared in the Athenceum, May 4th, 1839. The paragraph ran as follows: " Galvanic Engraving in Relief. While M. Daguerre and Mr. Fox Talbot have been dip- ping their pencils in the solar spectrum, J and astonishing us with their * Philosophical Magazine, 1836. t "Philosophical Transactions of the Royal Society," 1837. $ It was about this period that the famous Daguerreotype process of portrait- taking was being developed in England. JORDAN S PROCESS. 53 inventions [photographic], it appears that Professor Jacobi, at St. Petersburg, has also made a discovery which promises to be of little less importance to the arts. He has found a method if we under- stand our informant rightly of converting any line, however fine, engraved on copper, into a relief by galvanic process. The Emperor of Russia has placed at the professor's disposal funds to enable him to complete his discovery." Jordan's Process published. Having seen a copy of the above paragraph in the Mechanic's Magazine, May nth, 1839, Mr. J. C. Jordan, of London, eleven days afterwards sent a communication to the editor of that journal, in which he put in his claim if not to priority, as far as Jacobi was concerned, at least to prove that he had been experimenting in electro -deposition some twelve months before the announcement of Jacobi' s discovery was published in this country. Indeed, Jordan's communication did more, for it contained a definite process, and since this was undoubtedly the first publication of the kind which had appeared in England, the merit of originality so far as publication goes is clearly due to Jordan. As an important item in the history of electro -deposition, we give the subjoined extract from his letter from the Mechanic's Magazine, June 8th, 1839. The letter was headed " Engraving by Galvanism." Jordan's Process. " It is well known to experimentalists on the chemical action of voltaic electricity that solutions of several metallic salts are decomposed by its agency and the metal procured in a free state. Such results are very conspicuous with copper salts, which metal may be obtained from its sulphate (blue vitriol) by simply im- mersing the poles of a galvanic battery in its solution, the positive wire becoming gradually coated with copper. This phenomenon of metallic reduction is an essential feature in the action of sustaining batteries, the effect in this case taking place on more extensive sur- faces. But the form of voltaic apparatus which exhibits this result in the most interesting manner, and relates more immediately to the sub- ject of the present communication, maybe thus described : It consists of a glass tube closed at one extremity with a plug of plaster of Paris, and nearly filled with a solution of sulphate of copper. This tube and its contents are immersed in a solution of common salt. A plate of copper is placed in the first solution, and is connected by means of a wire and solder with a zinc plate, which dips into the latter. A slow electric action is thus established through the pores of the plaster which it is not necessary to mention here, the result of which is the precipitation of minutely-crystallised copper on the plate of that metal in a state of greater or less malleability, according to the slowness or rapidity with which it is deposited. In some experiments of thi& nature, on removing the copper thus formed, I remarked that the sur- 54 HISTORICAL REVIEW OF ELECTRO-DEPOSITION. face in contact with the plate equalled the latter in smoothness and polish, and mentioned this fact to some individuals of my acquaintance. It occurred to me therefore, that if the surface of the plate was engraved, an impression might be obtained. This was found to be the case, for, on detaching the precipitated metal, the more deli- cate and superficial markings, from the fine particles of powder used in polishing, to the deeper touches of a needle or graver, exhibited their corresponding impressions in relief with great fidelity. It is, therefore, evident that this principle will admit of improvement and that casts and moulds may be obtained from any form of copper. " This rendered it probable that impressions might be obtained from those other metals having an electro -negative relation to the zinc plate of the battery. With this view a common printing type was substi- tuted for the copperplate and treated in the same manner. This also was successful ; the reduced copper coated that portion of the type immersed in the solution. This, when removed, was found to be a perfect matrix, and might be employed for the purpose of casting when time is not an object. " It appears, therefore, that this discovery may possibly be turned to some practical account. It may be taken advantage of in procuring casts from various metals as above alluded to ; for instance, a copper die may be formed from a cast of a coin or medal, in silver, typemetal, lead, &c., which may be employed for striking impressions in soft metals. Casts may probably be obtained from a plaster surface sur- rounding a plate of copper ; tubes or any small vessel may also be made by precipitating the metal around a wire or any kind of sur- face to form the interior, which may be removed mechanically by the aid of an acid solvent, or by heat." [May 22nd, 1839.] It is a remarkable fact that Jordan's letter, regardless of the valu- able information it contained, commanded no attention at the time. Indeed, the subject of which it treated (as also did Jacobi's announced discovery), apparently passed away from public view, until a paper by Mr. Thomas Spencer, of Liverpool, was read before the Liverpool Philosophical Society on the I2th of September in the same year. Omitting the prefatory observations with which the paper commenced, its reproduction will form a necessary link in the chain of evidence respecting the origin of the electrotype process, and assist the reader in forming his own judgment as to whom the merit of the discovery is really due. Spencer's Paper on the Electrotype Process. "In September, 1837, I was induced to try some experiments in electro -chemistry with a single pair of plates, consisting of a small piece of zinc and an equal sized piece of copper, connected together with a piece of wire of the latter metal. It was intended that the action should be slow ; the SPENCER'S PAPER ON ELECTROTYPING. 55 fluids in which the metallic electrodes were immersed were in conse- quence separated by a thick disc of plaster of Paris. In one of the cells was sulphate of copper solution, in the other a weak solution of common salt. I need scarcely add that the copper electrode was placed in the cupreous solution, not because it is directly connected with what I have to lay before the society, but because, by a portion of its results, I was induced to come to the conclusion I have done in the following paper. I was desirous that no action should take place on the wire by which the electrodes were held together. To attain this object I varnished it with sealing-wax varnish ; but, in so doing, I dropped a portion of it on the copper that was attached. I thought nothing of this circumstance at the moment, but put the experiment in action. " The operation was conducted in a glass vessel ; I had, conse- quently, an opportunity of occasionally examining its progress. When, after the lapse of a few days, metallic crystals had covered the copper electrode, with the exception of that portion which had been spotted with the drops of varnish, I at once saw that I had it in my power to guide the metallic deposition in any shape or form I chose by a corresponding application of varnish or other non-metallic substance. " I had been long aware of what every one who uses a sustaining galvanic battery with sulphate of copper in solution must know, that the copper plates acquire a coating of copper from the action of the battery ; but I had never thought of applying it to a useful purpose before. My first essay was with a piece of thin copper-plate, having about four inches of superfices, with an equal-sized piece of zinc, connected together with a piece of copper wire. I gave the copper a coating of soft cement consisting of bees-wax, resin, and a red earth Indian or Calcutta red. The cement was compounded after the manner recommended by Dr. Faraday in his work on chemical manipulation, but with a larger proportion of wax. The plate re- ceived its coating while hot. On cooling, I scratched the initials of my own name rudely on the plate, taking special care that the cement was quite removed from the scratches, that the copper might be thoroughly exposed. This was put into action in a cylindrical glass vessel about half filled with a saturated solution of sulphate of copper. I then took a common gas glass, similar to that used to envelop an argand burner, and filled one end of it with plaster of Paris to the depth of three-quarters of an inch. In this I put some water, adding a few crystals of sulphate of soda to excite action, the plaster of Paris serving as a partition to separate the fluids, but sufficiently porous to allow the electro -chemical fluid to penetrate its substance. ' ' I now bent the wires in such a form that the zinc end of the arrangement should be in the saline solution, while the copper end 56 HISTORICAL REVIEW OF ELECTRO-DEPOSITION. should be in the cupreous one. The gas glass, with the wire, was then placed in the vessel containing the sulphate of copper. " It was then suffered to remain, and in a few hours I perceived that action had commenced, and that the portion of the copper rendered bare by the scratches was coated with a pure bright de- posited metal, whilst all the surrounding portions were not at all acted upon. I now saw my former observations realised ; but whether the deposition so formed would retain its hold on the plate, and whether it would be of sufficient solidity or strength to bear working if applied to a useful purpose, became questions which I now endeavoured to solve by experiment. It also became a question whether, should I be successful in these two points, I should be able to produce lines sufficiently in relief to print from. The latter appeared to depend entirely on the nature of the cement or etching ground I might use. "This last I endeavoured to solve at once. And, I may state, this appeared to be the principal difficulty, as my own impression then was that little less than |th of an inch of relief would be requisite. ' ' I then took a piece of copper, and gave it a coating of a modifica- tion of the cement I have already mentioned, to about ^th of an inch in thickness ; and, with a steel point, endeavoured to draw lines in the form of net-work, that should entirely penetrate the cement, and leave the surface of the copper exposed. But in this I experienced much difficulty, from the thickness I deemed it necessary to use ; more especially when I came to draw the cross lines of the net-work. When the cement was soft, the lines were pushed as it were into each other ; and when it was made of a harder texture, the intervening squares of net-work chipped off the surface of the metallic plate. However, those that remained perfect I put in action as before. ' ' In the progress of this experiment, I discovered that the solidity of the metallic deposition depended entirely on the weakness or intensity of the electro -chemical action, which I found I had in my power to regulate at pleasure, by the thickness of the intervening wall of plaster of Paris, and by the coarseness and fineness of the material. I made three similar experiments, altering the texture and thickness of the plaster each time, by which I ascertained that if the plaster partitions were thin and coarse, the metallic depositions proceeded with great rapidity, but the crystals were friable and easily separated ; on the other hand, if I made the partition thicker, and of a little finer material, the action was much slower, and the metallic deposition was as solid and ductile as copper formed by the usual methods, indeed, when the action was exceedingly slow, I have had a metallic depo- sition apparently much harder than common sheet copper but more brittle. SPENCER S PAFEK ON ELECTROTYPING. 57 " There was one most important (and, to me, discouraging) circumstance attending these experiments, which was that when I heated the plates to get off the covering of cement, the meshes of copper net-work invariably came off with it. I at one time imagined this difficulty insuperable, as it appeared to me that I had cleared the cement entirely from the surface of the copper I meant to have ex- posed, but that there was a difference in the molecular arrangement of copper prepared by heat and that prepared by voltaic action which prevented their chemical combination. However, I then determined, should this prove so, to turn it to account in another manner, which I shall relate in a second portion of this paper. I then occupied myself for a considerable period in making experiments on this latter section of the subject. ' ' In one of them I found on examination a portion of the copper deposition, which I had been forming on the surface of a coin, ad- hered so strongly that I was quite unable to get it off ; indeed, a chemical combination had apparently taken place. This was only in one or two spots on the prominent parts of the coin. I immediately recollected that on the day I put the experiment in action I had been using nitric acid for another purpose on the table I was operating on, and that in all probability the coin might have been laid down where a few drops of the acid had accidentally fallen. I then took a piece of copper, coated it with cement, made a few scratches on its surface until the copper appeared, and immersed it for a short time in dilute nitric acid, until I perceived, by an elimination of nitrous gas, that the exposed portions were acted upon sufficiently to be slightly corroded. I then washed the copper with water, and put it in action, as before described. In forty-eight hours I examined it, and found the lines were entirely filled with copper ; I applied heat, and then spirit of turpentine, to get off the cement ; and, to my satisfaction, I found that the voltaic copper had completely combined itself with the sheet on which it was deposited. " I then gave a plate a coating of cement to a considerable thick- ness, and sent it to an engraver ; but when it was returned, I found the lines were cleared out, so as to be wedge-shaped, or somewhat in form of a V, leaving a hair line of copper exposed at the bottom and broad space near the surface ; and where the turn of the letters took place, the top edges of the lines were galled and rendered ragged by the action of the graver. This, of course, was an important objection, which I have since been able to remedy in some respects by alteration in the shape of the graver, which should be made of a shape more resembling a narrow parallelogram than those in common use ; some of the engravers have many of their tools so made. I did not put this plate in action, as I saw that the lines, when in relief, would 58 HISTORICAL REVIEW OF ELECTRO-DEPOSITION. have been broad at the top and narrow at the bottom. I took another plate, gave it a coating of the wax, and had it written on with a mere point. I deposited copper on the lines and afterwards had it printed from. " I now considered part of the difficulties removed; the principal one that yet remained was to find a cement or etching-ground, the texture of which should be capable of being cut to the required depth, and without raising what is technically termed a burr, and at the same time of sufficient toughness to adhere to the plates where reduced to a small isolated point, which would necessarily occur in the operation which wood-engravers term cross-hatching. * ' I tried a number of experiments with different combinations of wax, resin, varnishes and earths, and also metallic oxides, all with more or less success. The one combination that exceeded all others in its texture, having nearly every requisite (indeed, I was enabled to polish the surface nearly as smooth as a plate of glass), was principally composed of virgin wax, resin, and carbonate of lead the white -lead of the shops. With this compound I had two plates, 5 inches by 7, coated over, and portions of maps cut on the cement, which I had intended should have been printed off and laid before the British Association at its meeting." Effect of Spencer's Paper. When Spencer's paper was published it at once commanded profound attention, and many persons practised the new art either for amusement or scientific research, while others turned their attention to it with a view to making it a source of com- mercial profit. It was not, however, until Mr. Robert Murray, in January, 1840, informed the members of the Royal Institution, London, that he had discovered a method of rendering non-conduct- ing surfaces such as wax, &c. conductive of electricity by employ- ing plumbago, or black lead, that the art became really popular in the fullest sense. This conducting medium was the one thing wanted to render the process facile and complete ; and soon after Mr. Murray's invaluable discovery had been made known, thousands of persons in every grade of life at once turned their attention to the electrotype process until it soon became the most popular scientific amusement that had ever engaged the mind, we may say, of a nation. The sim- plicity of the process, the trifling cost of the apparatus and materials, and the beautiful results which it was capable of yielding, without any preliminary knowledge of science, all combined to render the new art at once popular in every home. Every one practised it, including the youth of both sexes. It is not to be wondered at that an art so fascinating should have produced more than an ephemeral effect upon the minds of some of those who pursued it. Indeed, it is within our own knowledge that MR. DIECKS ON JORDAN'S DISCOVERY. 59 many a youth whose first introduction to chemical manipulation was the electro -deposition of copper upon a sealing-wax impression of a signet-ring or other small object, acquired therefrom a taste for a more extended study of scientific matters, which eventually led up to his devoting himself to chemical pursuits for the remainder of his days. At the period we refer to there were but few institutions in this country for the encouragement of scientific study. One of the most accessible and useful of these, however, was that founded by Dr. Birkbeck, the well-known Literary and Scientific Institution at that time in Southampton Buildings, London. Vindication of Jordan's Claim. Although Jordan's letter was published, as we have shown, three months prior to the reading of Spencer's paper in Liverpool, that important communication was overlooked, not only by the editor of the journal in which it appeared, but also by the scientific men of the period. Even the late Alfred Smee, to whose memory we are indebted for the most delightful work on electro -metallurgy that has appeared in any language, failed to recognise the priority of Jordan's claim. Impelled by a strong sense of justice, however, the late Mr. Henry Dircks wrote a series of articles in the Mechanic's Magazine in 1844, in which he proved that whatever merit might have been due to Spencer and Jacobi, Jordan was unquestionably the first to publish a process of electrotyping. Indeed, he went further, for he proved that the electro -deposition of copper had been accomplished practically long before the publication of any process. Before entering into the merits of Jordan's priority, Mr. Dircks makes this interesting statement : Mr. Dircks on Jordan's Discovery. ' ' The earliest application of galvanic action to a useful and ornamental purpose that I am acquainted with was practised by Mr. Henry Bessemer, of Baxter House, Camden Town, who, above ten years ago [about 1832] employed galvanic apparatus to deposit a coating of copper on lead castings. The specimens I have seen are antique heads in relief, the whole occupying a space of 3 inches by 4 inches. They have lain as ornaments on his mantel-piece for many years, and have been seen by a great number of persons." Appreciating from its historic and scientific interest the impor- tance of the above statement, it occurred to the author that if the means adopted at so early a period in electro -metallurgical history could become known, this would form an important link in the chain of research respecting the deposition of metals by electrolysis. He, therefore, wrote to Sir Henry Bessemer, requesting him to furnish such particulars of the method adopted by him in depositing copper upon the objects referred to as lay in his power after so long a period of time. "With kind courtesy, and a generous desire to comply with 60 HISTORICAL REVIEW OF ELECTRO-DEPOSITION. the author's wishes, Sir Henry took the trouble to furnish the infor- mation conveyed in the following interesting communication, which cannot fail to be read with much gratification by all who have studied the art of electro-deposition, either from its scientific or prac- tical aspect. When we call to remembrance the numerous inventions with which the active mind of Sir Henry Bessemer has been associated during the greater portion of the present century, culminating in his remarkably successful improvements in the manufacture of steel, it is pleasing to read that at the youthful age of eighteen when voltaic electricity was but little understood, and Daniell's, Grove's, and Smee's batteries unknown he was engaged in experiments with metals, which were evidently conducted with an amount of patience and careful observation which would have been highly creditable in a person of more advanced years. Sir Henry Bessemer's Experiments. Replying to the author's inquiry as to the method he adopted in coating with copper the objects referred to above, Sir Henry, in January of the present year, wrote as follows : the minuteness of the details given, after so great a lapse of time, will doubtless strike the reader with some astonish- ment : " I have much pleasure in replying to your note of inquiry in reference to the deposition of copper from its solutions on white metal castings. "My first experiments began when I was about eighteen years of age, say in 1831-2. At that period, after much practice, I was most successful in producing castings of natural objects in an alloy of tin, bismuth, and antimony. In this alloy I cast such things as beetles, frogs, prawns, &c. ; also leaves of plants, flowers, moss-rose buds ; and also medallions, and larger works in basso-relievo. By my system of casting in nearly red-hot metal, the metal was retained for ten or fifteen minutes in a state of perfect fluidity in the mould, and hence, by its pressure, forced itself into every minute portion of the natural object, whatever it might be ; thus every minute thorn on the stem of the rose was produced like so many fine projecting needles. I exhibited several of these castings, coated with copper, at ' Topliss's Museum of Arts and Manufactures,' at that time occupy- ing the site of the present National Gallery, and which museum was afterwards removed to a large building is. Leicester Square, now the Alhambra Theatre, where I also exhibited them. "Beautiful as were the forms so produced, they had a common lead-like appearance, which took much from their value and artistic beauty, and as a remedy for this defect, it occurred to me that it was possible to give them a thin coat of copper, deposited from its solu- tion in dilute nitric acid. This I made by putting a few pence [copper SIR H. BESSEMER'S EXPERIMENTS. 61 coins were in currency in those days] into a basin with water and nitric acid. My early attempts were not very successful, for the depo- sited metal could be rubbed off, and was in other ways defective. I next tried sulphate of copper, both cold and boiling solutions. I found the sulphate much better adapted for the purpose than the nitrate solution. At first I relied on the property which iron has of throwing 1 down copper from its solutions, and by combining iron, in comparatively large quantities, with antimony, and using this alloy with tin, bismuth, and lead, I succeeded in getting a very thin, but even, coating of copper ; but it was not sufficiently solid, and easily rubbed off. " In pursuing my experiments, I found that the result was much improved by using a metallic vessel for the bath instead of an earthen- ware one, such as a shallow iron, tin, or copper dish, as a slight galvanic action was set up, but the best results were obtained by using a zinc tray, on the bottom of which the object was laid, face upwards, and the solution then poured in. By this means a very firm and solid coating was obtained, which could be burnished with a steel burnisher without giving way. By adding to the copper solution a few crystals of distilled verdigris, I obtained some beautiful green bronze deposits, a colour far more suitable .for medallions and busts than the bright copper coating obtained by the sulphate when used alone. " I cast and coated with green copper a small bust of Shakespeare, which, with many other specimens, I sold to Mr. Campbell, the sculptor, who at that time was modelling a life-sized bust of Canning : he had arranged that I should cast it from the "lost- wax," and deposit green copper thereon. Unfortunately Campbell died before his model was completed. But for this incident I might possibly have carried the depositing process much further, but at that time my suc- cess in casting, in a very hard alloy, dies used for embossing card- board and leather, offered a more direct and immediate commercial result, and thus the artistic branch was lost sight of. I remember showing some of these castings to my friend the late Dr. Andrew Ure, about the year 1835-6, with which he was much pleased. In referring to them several years later, in the second edition of his supplement to his ' Dictionary of Arts and Manufactures,' published in 1846, he mentions these castings as lead castings, at page 7> under the head of ' Electro -Metallurgy,' which commences in these words : " ' Electro- Metallurgy. By this elegant art, perfectly exact copies of any object can be made in copper, silver, gold, and some other metals, through the agency of electricity. The earliest application of this kind seems to have been practised about ten years ago, by Mr. Bessemer, of Camden Town, London, who deposited a coating of 62 HISTORICAL REVIEW OF ELECTRO-DEPOSITION. copper upon lead castings so as to produce antique heads, in relief, about three or four inches in size. He contented himself with form- ing a few such ornaments for his mantel-piece, and though he made no secret of his purpose, he published nothing upon the subject. A letter of the 22nd of May, 1839, written by Mr. C. Jordan, which ap- peared in the Mechanic's Magazine for June 8th following, contains the first printed notice of the manipulation requisite for obtaining electro -metallic casts, and to this gentleman, therefore, the world is indebted for the first discovery of this new and important application of science to the uses of life.' ' ( The first inception of the idea of coating works of art in metal with a deposited coating of another metal, if not resting solely with me, at least I certainly was within measurable distance of this great discovery some three or four years before it was brought forward by any other person, but I failed to see its true significance, and conse- quently lost a grand opportunity. " You are quite at liberty to make any use you like of this informa- tion." We will now return to Mr. Dircks' vindication of Jordan's claim. Referring to Jordan's letter to the Mechanic's Magazine, Mr. Dircks says, l ( In particular I would direct attention to the fact of the main incidents named by Mr. Jordan, published June 8th, 1839, agreeing with those published by Mr. Spencer, September I2th, 1839, and, curious enough, being called forth by the same vague announcement of Professor Jacobi's experiments which was then making our round of periodicals. Both parties described Dr. G-olding Bird's small galvanic apparatus ; one used a printer's type, the other a copper coin, and both recommend the application of heat to remove the precipitated copper. " I was aware of Mr. Jordan's letter at the time of its publication, and have frequently been surprised since that his name has not transpired in any discussion I have heard upon the subject. Nothing can be clearer than his reasoning, the details of his experiments, and his several concluding observations." Dr. Oolding Bird's Experiments. There can be no doubt what- ever that after Dr. G-olding Bird published the results of his interest- ing experiments in 1837, and the means by which he obtained his im- portant results, many scientific men devoted themselves to investigating the new application of electricity, amongst whom was Mr. Henry Dircks. "It was particularly in September and October, 1837," wrote Mr. Dircks, " that several parties attached to scientific pursuits in Liver- pool, were engaged in repeating the experiments of Dr. G-olding Bird, and of which he gave an account before the chemical section of the British Association at Liverpool, over which Dr. Faraday presided. DR. GOLDING BIRD'S EXPERIMENTS. 63 The apparatus used on that occasion by myself and others was pre- cisely that recommended by Dr. Bird, consisting of simply any glass vessel capable of holding a solution of common salt, into which is in- serted a gas lamp chimney, having its lower end plugged up by pour- ing into it plaster of Paris ; a solution of sulphate of copper is then poured into it, and the whole immersed into the contents of the glass, and tightened with pieces of cork. The result expected from this arrangement was the deposit of metallic veins of the copper within the plaster diaphragm, independent of any connection with the poles of the battery. Dr. Faraday, and every other electrician, expressed surprise and doubt at the results in this respect said to have been obtained by Dr. Bird ; and Dr. Faraday particularly urged the neces- sity and importance of caution in receiving as established a result so greatly at variance with all former experience, and proceeded to explain a variety of causes tending to lead to fallacious results in the curious and interesting experiments." Up to this time, the possibility of obtaining electrical effects by means of a single metal, in the manner pursued by Dr. Bird, would have been considered theoretically impossible. It must not be wondered at, therefore, that even the greatest of our philosophers Michael Faraday should have been sceptical in the matter. It is clear now, however, that Dr. Golding Bird's results were based upon principles not then understood, and that to this gifted physician we are indebted for what is termed the " single - cell " voltaic arrange- ment the first, and for some time after the only, apparatus employed in producing electrotypes. Origin of the Porous Cell. It appears that while Mr. Dircks was experimenting (in 1837) in obtaining crystals of copper by Dr. Bird's method, he was frequently in communication with Mr. John Dancer, a philosophical instrument maker in Liverpool, and in October of the following year (1838) that gentleman showed him a " ribbon of copper, thin, but very firm, granular on one side, while it was bright and smooth, all but some raised lines, on the other." This result, Mr. Dancer informed him, was obtained by galvanic action, observing that some specimens were as tenacious as rolled copper, while others were crystalline and brittle. Mr. Dancer attributed the superiority of the former to the following cause : ' ' Having gone to the potteries to look out suitable jars for sustaining batteries, and having fixed on a lot which he was told would not answer as they ivere not glazed, and would not hold liquor," it occurred to him that such unglazed jars might be turned to account, and used instead of bladder, brown paper plaster of Paris, and other porous substances he had previously em- ployed. Having obtained a sample for experiment, he subsequently found that he could obtain a more firm and compact deposit of copper 64 HISTORICAL REVIEW OF ELECTRO-DE POSITION. than in any previous experiment. To the accidental circumstance above referred to, we are undoubtedly indebted for that most import- ant accessory to the single -cell apparatus and the two -fluid battery the porous cell. In a letter to Mr. Dircks, relative to Spencer's claim to the discovery of a means of obtaining " metallic casts " by electro -deposition, Mr. Dancer says, "I met Mr. Spencer one morning in Berry Street, Liverpool, and happened to have one of these precipitated copper plates with me, which I showed to him. When I told him how it had been formed he would scarcely believe it, until I pointed out the im- pressions in relief of all the minute scratches that were on the plate against which it had been deposited. The surprise that Mr. Spencer expressed very naturally led me to suppose that it was the first com- pact piece of precipitated copper he had seen." At this early period (1838) Mr. Dancer had not only deposited tough reguline copper, but he went a step farther. He attached to a copper plate, by means of varnish, ' ' a letter cut out from a printed bill. The copper precipitated on all parts of the plate, except where the letter was fixed ; when I peeled the precipitated copper off, the letter came out, not having connection with the outside edge. I also obtained an impression by stamping my name on a copper cylinder, the impression being the reverse way All this happened many months before I was aware that Mr. Spencer had been engaged in anything of the kind, except that he had Dr. Bird's experiments in action. Sometime after this Mr. Spencer applied to me for one of my porous jars, and one day at his house he told me for what purpose he wanted it." It is perfectly evident that Mr. Dancer's results were obtained long before the publication of Spencer's paper, and that both were indebted to Dr. Golding Bird's simple but ingenious contrivance for prose- cuting their first experiments ; and it is also clear that Dancer's brilliant idea of substituting porous earthenware for the crude plaster diaphragms greatly facilitated experimental researches in this direction ; while at the same time it placed within our reach one of the most valuable accessories of the two -fluid voltaic battery the porous cell. Being desirous of placing Jordan's claim to priority as the first to make publicly known the process of electrotyping, or electrography r , as he termed it Mr. Dircks followed up the subject in the Mechanic's Magazine, in a series of papers, in which he not only traced Mr. Spencer's experiments to their true origin, namely, Dr. Bird's experiments published two years before, and the hints which he had derived from Dancer, but he moreover stowed that Spencer must have been aware of Jordan's published process, for he says, in summing up the evidence he had produced against Spencer's position DIBCKS ON SPENCER'S CLAIM. 65 in the matter thus : "Lastly, therefore, that through the Mechanic's Magazine (which Mr. Spencer was regularly taking in) the experimental results obtained by Mr. Dancer, and the reports in April and May, 1839, in public papers, of Jacobi's experiments, all being broad hints, and abundant assistance to aid Mr. Spencer, that he is rather to be praised for his expression of what was already known, on a smaller and less perfect scale, than to be adjudged a discoverer, much less the father of electro -metallurgy, having a preference to every other claimant." Following the paper from which the foregoing extract is taken, is a footnote by the Editor of the Mechanic's Magazine, which is important as showing how strange it was that Jordan's communication* not only escaped the attention of scientists, but even that of the con- ductor of the journal in which it appeared : " Mr. Dircks has proved beyond all doubt that we have made a great mistake in advocating so strenuously the claims of Mr. Spencer to the invention of electro - graphy. No one, however, can suppose that we would intentionally exalt any one at the expense of our own journal, which we are now pleased to find was the honoured medium of the first distinct revela- tion of this important art to the public, by an old and esteemed correspondent of ours, Mr. Jordan. Whatever Mr. Bessemer, Mr. Dancer, Mr. Spencer, or others, may have previously said or done, it was in private made no secret of, perhaps, but still not communicated to the public at large not recorded in any printed work for general benefit. For anything previously done by any of them, they might have still remained in the profoundest obscurity. No public descrip- of an earlier date than Mr. Jordan's can, we believe, be produced ; and when we look upon that description, it is really surprising to see with what fulness and precision the writer predicated of an art nearly all that has been since accomplished. In supporting, as we did, the claims of Mr. Spencer to be considered as the first discoverer, we had lost all recollection of Mr. Jordan's communication. We have no personal acquaintance with either of the gentlemen, and could have no motive for favouring one more than the other. We took up the cause of Mr. Spencer with spontaneous warmth because we thought him to be a person most unfairly and ungenerously used, as in truth he was so far as the intention went, by those who, having at the time none of those reasons we now have for questioning Mr. Spencer's pretensions, yet obstinately refused to acknowledge them. If it should seem to the reader more than usually surprising that Mr. Jordan's paper escaped the recollection of the editor, through whose hands it passed to the public, his surprise will be lessened, perhaps, when he observes how it appears to have escaped notice, or been passed over in silence, by every one else down to the present moment even those, not a few, who have expressly occupied themselves in electrography To us, 66 HISTORICAL REVIEW OF ELECTRO-DEPOSITION. the most surprising thing of any connected with the case is, that neither Mr. Jordan himself, nor any of his friends, should before now have thought it worth while to vindicate his claims to the promulga- tion of an art which justly entitles him to take a high place among the benefactors of his age and country. Ed. M. M." While Mr. Dircks' " Contributions to the History of Electro-Metal- lurgy ' ' were being published in the columns of the Mechanic's Magazine, the arguments and facts which he adduced created a deep impression in the minds of scientific men of the day, who had unfortunately accepted Spencer as the originator of electrotypy. Of all men, scien- tists are the most anxious to accord the merit of discovery to those who are really entitled to it. Devoting themselves to the investigation of natural laws, and their application to the useful purposes of man, they are naturally jealous of any attempt on the part of one to appro- priate the honour usually the only reward due to another. It is not surprising, therefore, that when it became fully proved that to Jordan and not Spencer was due the credit of having been the first to publish a process for the practical deposition of copper by electro- lysis, that such men should frankly acknowledge their mistake. Amongst those who came forward to do justice to Jordan's claim were the late Professor Faraday, Dr. Andrew Ure, and Professor Brande, then chemist to the Royal Mint. The latter eminent chemist and author of the best chemical manual in our language, sent the following letter to Mr. Dircks, which clearly acknowledges the error into which, in common with others, he had fallen in attributing to Spencer the merit of the electrotype process : " I am much obliged by your copy of the Mechanic's Magazine and the information it contains respecting Mr. Spencer's pretensions. I certainly always gave him credit for much more merit than he appears to have deserved." When Spencer found that his position was so severely shaken by Mr. Dircks' powerful defence of Jordan's claim to priority, he wrote several letters in reply, which appeared in the columns of the above journal, with a view to refute his opponent's arguments, and shake his testimony ; but in this he was unsuccessful, for the facts which Mr. Dircks had made known were absolutely beyond refutation. It is not often that men of science enter into a controversy of this nature, but silence under such circumstances would have been an act of injus- tice to Jordan, by leaving the question still in doubt. Amongst those who ascribed to Spencer the discovery of the elec- trotype process was Mr. George Shaw, of Birmingham, in the first edition of his " Manual of Electro -Metallurgy." In the second edition of his work, however, he made the amende to Jordan, by frankly acknowledging his mistake. The following letter from the DIRCKS ON SPENCER'S CLAIM. 67 late Dr. Andrew Ure to Mr. Dircks shows how fully he recognised that gentleman's advocacy of Jorda-n's claim: "I read with great interest your narrative of the discovery or invention of the electrotype art, and am much pleased to see justice done to modest retiring merit in the persons of Mr. Jordan and Mr. Dancer. The jay will feel a little awkward this cold weather, stripped of his peacock plumage." The following letter from Faraday tends to show that the great philosopher, in common with most other persons, had, prior to Mr. Dircks' explanation of the facts, believed in Spencer being the origi- nator of electrotyping : "I am very much obliged by your kindnesf in sending me your account of the facts, &c., &c. It is very valuable as respects the fixing of dates, and has rather surprised me." * It is a pity, but none the less true, that while Jordan's communica- tion received no attention whatever, although published in a well- read journal, Spencer's paper which had merely been read before a local society in Liverpool, and afterwards printed for private circulation only commanded the profoundest attention. In short, to use a common phrase, it "took the world by storm." The name of " Spencer, the discoverer of Electrotyping," was on every lip, and men of science of all nations regarded him as one who had made a great addition to the long roll of important discoveries which science had placed at the disposal of art. Henry Dircks' champion- ship of Jordan's just claim, however, eventually broke up Spencer's position, and to the first publisher of the electrotype process, Mr. C. J. Jordan, was at last accorded the merit for he received no other recog- nition of having published a process, if we may not say discovery, which was destined to prove of inestimable advantage to his fellows, not only in itself, but as being the means by which the minds of men were directed to the deposition of other metals by electrical agency. It would not be out of place to suggest that in commemoration of Jordan's gift to mankind of so useful and valuable a process, an appropriate testimonial should be set on foot if not by the public, at least by those who have directly gained so much by his initiation of the art of electro -deposition. The success which attended the electrotype process induced many persons to turn their attention to the deposition of gold and silver, by means of the direct current; but up to the year 1840 no really suc- cessful solution of either metal was available. In that year Mr. John "Wright, a surgeon in Birmingham, and Mr. Alexander Parkes, in the employment of Messrs. Elkington, were engaged in making experiments in electro -deposition, when the former gentleman hap- * The three foregoing letters, which wo transcribed from the originals, are now, we believe, published for the first time. 68 HISTORICAL REVIEW OF ELECTRO-DEPOSITION. peued to meet with a passage in Scheele's " Chemical Essays," in which he found that cyanides of gold, silver, and copper, were soluble in an excess of cyanide of potassium. It at once occurred to him that solutions of gold and silver thus obtained might be employed in electro-deposition, and he then formed a solution by dissolving chloride of silver in a solution of ferro- cyanide of potassium, from which he obtained, by electrolysis, a stout and firm deposit of silver, a result which had never before been obtained. A few weeks after, Mr. Wright prepared a solution with cyanide of potassium, instead of the ferro -cyanide, and although various cyanide solutions of silver and copper had already been employed in the simple immersion process of depositing these metals, there is no doubt that it is to Mr. Wright that we are really indebted for the practical application of cyanide of potassium as a solvent for metallic oxides and other salts used in electro -deposition. About this time (1840) Messrs. EMngton were preparing to take out another patent, when Mr. Wright, having submitted his results to them, agreed to include his process in their patent, in consideration of which it was agreed that he should receive a royalty of one shilling per ounce for all silver deposited under the patent : on his decease, which took place soon afterwards, an annuity was granted to his widow. This patent, with Wright's important addition, namely the employment of alkaline cyanides, formed the basis of the now great art of electro -gilding and plating : but it was some time before the proper working strength of baths and the pro- portion of cyanide could be arrived at, the deposits being frequently non-adherent, which caused them to strip or peel off the coated articles in the process of burnishing. This was afterwards remedied to some extent by dipping the articles (German silver chiefly) in a very dilute solution of mercury. About this time, the author, in conjunction With his brother, Mr. John Watt, introduced electro-gilt and silvered steel pens, which were sold in considerable quantities. In the same year, Mr. Murray discovered a means of rendering non-conducting surfaces, as wax, &c., conductive, by coating them with powdered plumbago, and this important suggestion proved of inestimable advantage to those who desired to follow the art of electrotyping commercially. Indeed, without the aid of this useful substance, it is doubtful whether the important art would have greatly exceeded the bounds of experiment. At this period, also, another important improvement in the electrotype process was introduced by Mr. Mason, which consisted in employing a separate battery as a sub- stitute for the " single -cell" process up to that time adopted in electrotyping. By the new arrangement, a copper plate was con- nected to the positive pole of a Daniel! Battery, while the mould to be coated with copper was attached to the negative pole. When these were immersed in the electrotyping bath (a solution of sulphate of DIECKS ON SPENCER'S CLAIM. 69 copper), under the action of the current the copper-plate became dis- solved as fast as pure copper was deposited upon the mould, whereby the strength of the solution was kept in an uniform condition. It is this method which is now almost universally adopted (when dynamo machines are not employed) in practising the art of electrotyping upon a large scale. In 1841, Mr. Alfred Smee published his admirable work on Electro- metallurgy, which at that period proved of the greatest service to all persons interested in the new art. In the year following, Mr. J. S-. Woolrich introduced his magneto -electric machine, which for many years after occupied a useful position as a substitute for voltaic batteries, in several large plating works. In this year also, Dr. H. E. Leeson took out a patent for improvements in electro -depositing processes, in which he introduced the important elastic moulding material, " guiding wires," keeping articles in motion while in the bath, &c. In 1843, Moses Poole obtained a patent for the use of a thermo- electric pile as a substitute for the voltaic battery ; but the invention was not, however, successful. Many patents were taken out in the following years for various processes connected with electro -deposi- tion ; but the next most important improvement was due to Mr. W. Milward, of Birmingham, who accidentally noticed that after wax- moulds, which had been covered with a film of phosphorus by apply- ing a solution of that substance in bisulphide of carbon to their surfaces had been immersed in the cyanide of silver plating bath, the silver deposit upon other articles, such as spoons and forks, for example, which were afterwards coated in the same bath, presented an unusually bright appearance in parts, instead of the dull pearly lustre which generally characterises the silver deposit. This incident induced Mr. Milward to try the effect of adding bisulphide of carbon to the plating bath, which produced the desired result. For some time he kept the secret to himself ; but finding that it eventually became known, he afterwards patented the process in conjunction with a Mr. Lyons, who had somehow possessed himself of the secret. From that time the addition of bisulphide of carbon to silver baths for the pur- poses of " bright " plating has been in constant use. Further reference to subsequent inventions connected with the art will be found in other chapters. In the foregoing sketch of the origin and history of electro -deposi- tion we have endeavoured to give such information as we hoped would be interesting to many who are engaged in the art, and also instructive to those who may be about to enter into a study of tho subject, believing that the work would be incomplete without some special reference to the interesting origin of so great and useful an art. CHAPTER V. THEORY OF ELECTROLYSIS. Chemical Powers of the Voltaic Pile. Faraday's Nomenclature of Electro- chemical Action. Direction of the Current. Decomposition of Water. Action of the Electric Current upon Compound Substances. Electro- lysis of Sulphate of Copper. Electrolysis of Sulphate of Potash, &c. Electrical Transfer of Elements. Practical Illustrations of the Electro- lytic Theory. Chemical Powers of the Voltaic Pile. We are indebted to Nicholson and Carlisle for the discovery of the chemical powers of the voltaic pile, which were first observed in the decomposition of water, and subsequently of certain saline solutions, in the year 1800. The subject was afterwards more closely investigated by Hisinger and Berzelins, in 1803, and in 1807 Sir Humphrey Davy, who had been experimenting in the same direction, delivered his famous lecture " On some Chemical Agencies of Electricity," before the Royal Society, in which the electro -chemical powers of the pile were more minutely demonstrated, and which formed the basis of some splendid discoveries made by that gifted philosopher, including the great dis- covery of the decomposition of the fixed alkalies. Many later experi- mentalists devoted their attention to this field of research, but more especially Faraday, to whose indefatigable labours and profound reasoning we are indebted for a clear exposition of the laws which govern electro -chemical decomposition, or Electrolysis, as also for a host of discoveries which have proved of inestimable service to the devotees of electrical science. His < ' Experimental Researches in Electricity " contain the results of his labours in this department of science, and "they have not only explained," says Brande, a and enlightened much that was before unintelligible and obscure in regard to statical electricity, but have also stamped a new character upon electrical as connected with chemical science ; in point of originality in devising experiments, skill in carrying them into effect, and per- spicuity in tracing out and unravelling the complicated relations and bearings of the new truths which are elicited, Faraday stands, if not unrivalled, at least unsurpassed." Faraday's Nomenclature of Electro-chemical Action. The DIRECTION OF THE CURRENT. free ends of the conducting wires of a voltaic battery, generally- termed the positive and negative poles, are those sufaces by which the electric current enters and leaves the battery, simply acting as a pathway for the current. This being so, Faraday adopted the term electrode, as a substitute for pole, the word being derived from rjXtKTpov and oSog, a way, thereby signifying that substance or surface, whether of air, water, or metal, which bounds the extent of the decomposing matter, in the direction of the current. The conductors immersed in the liquids to be decomposed by the current are therefore termed, respectively, the positive and negative electrodes. The conductor by which the current enters the liquid he terms the anode (from ava, upwards, and odog, a way], and that by which it leaves the liquid the cathode (from Kara, dowmvards, odog, a way], assuming the current of electricity to follow the passage of the sun that is to pass from east to west in its rising and setting. Faraday also applied the terms anelectrode and cathelec- trode for the respective poles of the battery. All substances which are susceptible of direct decomposition by the current are called electro- lytes; the process of electro -chemical decomposition is termed electro- lysis, and for electro-chemically decomposed, he substituted electrolysed. The elements of the electrolysed liquid which are liberated by the action of the current are termed ions, those set free at the anode, or positive electrode, being termed anions, and those at the cathode, or negative electrode, cations. Thus, when acidulated water is electrolysed, two ions are evolved, namely oxygen and hydrogen, the former at the positive, and the latter at the negative electrode. Direction of the Current. In the simple voltaic circle, as shown in Fig. 42, z represents a plate of zinc, and s a plate of silver, Fig. 42. Fig. 43. immersed in a vessel containing dilute sulphuric acid. The darts indicate the current passing from the zinc through the liquid to the silver, and returning through the conducting wire to the zinc; z therefore represents the positive metal in relation to s through the liquid, and s the negative metal in relation to z through the liquid. If separate wires are employed, as in Fig. 43, the current would pasi 72 THEORY OF ELECTROLYSIS. as before from the positive metal z to the negative metal s, traversing the conducting wire, in the direction of the darts, so that P would become the positive electrode, or anode, and N the negative electrode, or cathode. The metal which becomes dissolved in a voltaic couple is always the positive or active metal (as zinc, for example) upon which oxygen, chlorine, and other anions (electro - negative bodies) are evolved ; the inactive or passive metal (as silver, platinum, &c.) is the negative, and upon it hydrogen and the metals or other cations (electro -positive bodies) are evolved in all cases of electrolytic action. If the above voltaic pair were immersed in a solution which would act upon the silver, and not upon the zinc, the electrical order would be reversed, the silver would become the positive metal and the zinc negative. One of the indispensable conditions of electrolysis is fluidity, and when a liquid is decomposed by electricity, or electrolysed, its constituents are disengaged solely at the poles or electrodes that is where the current enters and leaves the liquid, the remainder being in a comparatively undisturbed state. "We say comparatively, for we have always observed that the liquid, from the moment the current enters it, and during the entire progress of the electrolytic action, is kept in continual, though almost imperceptible, motion. It had generally been supposed, according to the old electro- chemical theory, that the electro -positive bodies (cations] and electro- negative bodies (anions} were under the influence of direct attractive forces residing in the opposite poles of the voltaic battery ; but Faraday proved, by conclusive experiments, that the "decomposing force is not at the poles, or electrodes,* but within the substance acted upon by the current, and the terms he has introduced express the phenomena which are observable in all cases of electro -chemical decomposition. The decomposing effects produced by the voltaic current in different electrolytes are precisely in accordance with the atomic weights or chemical equivalents (which see) of the substances electrolysed. For example, if the current be made to act upon acidulated water, a solution of iodide of potassium and a solution of chloride of lead, these three electrolytes will all undergo decomposition at the same time, but to a very different extent. The electric current required to decom- pose 9 parts of water, will separate into their elements 166 parts of iodide of potassium, and 139 parts of chloride of lead. In other words, the same amount of electricity that would reduce 56 parts of iron from its solution to the metallic state, would reduce 207 parts of lead, or 108 parts of silver. Decomposition of Water. In order to understand the principles * By common consent these terms are used indiscriminately. DECOMPOSITION OF WATER. 73 of electrolysis, it will be necessary to have recourse to a few experi- mental illustrations, which we will endeavour to render as simple and as brief as possible. Fig. 44 represents a glass globe a with three openings, two of which are at the sides and are fitted with corks, perforated to admit glass tubes of such length as to meet near the centre of the globe. Each of these tubes is traversed by a platinum wire bent in the form of a hook at one end, and connected at the other end to a strip of platinum foil, these latter being adjusted so as to stand erect within the tenth of an inch of each other. A glass tube b is inverted into the neck of the globe, in which a notch is filed to allow a portion of the fluid to ooze out. The globe is now to be filled with water acidu- lated with sulphuric acid, and the two hooked Fig. 44- ends of the platinum wire connected to the conducting wires of a voltaic battery. The moment the circuit is thus completed, bubbles of gas arise in the tube, displacing the liquid, which trickles out of the neck of the globe. "While the decomposition is going on, it will be noticed that twice the quantity of gas escapes from the platinum plate in communication with the cathode or negative pole, as compared with that liberated at the anode or positive electrode. The inverted tube now contains a mixture of oxygen and hydrogen gases, in the proportion of two volumes of the latter to one volume of the former ; and if it be again inverted (its mouth being closed by the thumb while doing so), and the mouth of the tube brought near a lighted match, upon removing the thumb an explosion will take place, when the gases re-combine, form- ing water. By another experiment the gases may be collected in separate tubes which, for the purpose of estimating their relative propor- tions, in volume, should be graduated into cubic inches. Such an arrangement is shown in Fig. 45, in which a globe with two necks, each having a tube so connected as to receive the gas liberated at each electrode. As the decomposition progresses, it will be observed that rather more than double the quantity of gas occupies the tube inverted over the negative pole to that contained in the tube enclosing the positive pole. If a lighted match be applied to the tube containing Fig- 45- 74 THEORY OF ELECTROLYSIS. the hydrogen, this gas will quietly burn with a pale blue flame ; and if an ignited match be blown out, and the glowing end plunged into the tube containing the oxygen, it will instantly be rekindled into a flame ; but if the mouths of the two tubes be brought simultaneously near the flame of a candle a violent explosion will take place as before. If, in the foregoing experiments, the poles be reversed, the results will be precisely the same, that is to say, hydrogen will be evolved at the negative and oxygen at the positive pole. Besides the decompos- ing power of the current which these simple experiments illustrate, they also exhibit the composition of water both as regards its constituents and the proportions in which they are combined. Thus, if the volume of each gas be reduced to its actual weight the volume of hydrogen being represented by I the half- volume of oxygen will be = 8, since the specific gravity of hydrogen and oxygen is as I to 16 ; the nine parts of water, therefore, consist of one part, by weight, of hydrogen, and eight parts, by weight, of oxygen ; or by volume, I part hydrogen and 1 6 parts oxygen. Action of the Electric Current upon Compound Substances. When solutions of neutral salts, as sulphate of soda, for example, are subjected to the action of the electric current, or electrolysed, they yield acids and alkalies, the former always at the positive electrode, and the latter at the negative. "When solutions of metallic salts are electrolysed, oxygen and the acids are developed at the positive, and hydrogen and the metals at the negative pole. To illustrate the decomposition of a neutral salt, we may take a solution of sulphate of soda (Glauber's salt). A glass tube is bent in the form of a syphon, as indicated in Fig. 46, and placed in a wine-glass as a support. The syphon-tube is now to be filled with a weak solution of sulphate of soda tinted blue with tincture of litmus ; a platinum wire or strip of platinum foil, soldered to a wire of the same metal, is now to be intro- duced into each leg of the syphon, but must not be allowed to come in contact at the bend of the tube. One of the platinum wires is now to be connected to the negative, and the other to the positive terminals of a voltaic battery, when, Fig. 46. in a short time, the blue colour of the liquid, in which the negative electrode is placed, will be changed to green, while the fluid in which the positive electrode is inserted will have acquired a red colour. The former indicates the presence of an alkali, and the latter of an acid;* in other words, the * Vegetable blues are always turned red by acids, Fig. 47- ELECTROLYSIS OP SULPHATE OF COPPER. 75 soda is set free at the one pole, and the sulphuric acid at the other. If the poles be now reversed, the respective colours will also, after a time, become reversed. A modification of the above experiment consists of the following arrangement : Two tubes (Fig. 47), each furnished with a strip of platinum connected to a wire of the same metal, are to be filled with the blue solution of sulphate of soda, and inverted in two separate glasses also nearly filled with the same liquor. The two glasses are to be connected together by means of a syphon -shaped tube filled with the same solution. If the platinum wires N and p be now connected to a voltaic battery, in a short time it will be observed that, notwithstanding their being in separate Vessels, the blue liquor will, as in the foregoing experiment, become red and green respectively. Moreover, if the voltaic action be kept up for a sufficient length of time, the alkali of the salt will have passed from p to N and the acid from N to p. It thus appears that the acid and alkali of the sulphate of soda have traversed the connecting syphon in oppo- site directions, and it is inferred that, under the influence of electrical attraction, the usual chemical affinities become suspended, otherwise the acid and alkali would unite (which is not the case) in their transit through the tube. Further examples of the transfer of elements are given at page 76. Electrolysis of Sulphate of Copper. A very simple but instruc- tive experiment in electrolysis is the following : Make a moderately strong solution of sulphate of copper and nearly fill a glass tumbler with the liquid, as in Fig. 48. Now connect two strips of platinum foil to the terminals of a battery, and immerse them in the copper solution. In a few moments a bright deposit of pure metallic copper will appear upon the negative electrode N, while the positive will exhibit no change. If the poles be now reversed, by disconnecting the conducting wires from the binding -screws of the battery and reversing their position, the copper will speedily disappear from the Fig. 48. 76 THEORY OF ELECTROLYSIS. negative (noiv the positive) electrode, having become dissolved in the solution, and a deposit of the metal -will appear upon the other pole. In this result we observe that the metallic deposit always takes place upon the negative terminal of the voltaic battery (that which is connected to the zinc or positive element], while the copper, which had been deposited upon the negative electrode in the first experiment, soon disappears when the poles are reversed, the copper -coated strip being converted into the anode or positive electrode. Hence we see (by the fact of the copper becoming dissolved in the solution) the use of anodes or dissolving plates in the practical deposition of metals by electricity. Electrolysis of Sulphate of Potash, &c. Davy, in his remark- able paper on "Some Chemical Agencies of Electricity," before referred to, described the following interesting experiment, which at the time created the most profound astonishment, since the only way in which the results could be explained was by assuming that throughout the whole circuit the natural affinities of substances are suspended, but again restored when they are dismissed at the electrodes by which they were attracted : "An arrangement was made consisting of three vessels, as shown in Fig. 49. A solution of ' ~" il^Jil^ ^^H^i " N sulphate of potash was placed in contact with the negatively electrified point, pure water was placed in contact with the positively electrified point, and a wea k solution of ammonia was made the middle link of the conducting chain, so that no sulphuric acid could pass to the positive point in the distilled water without passing through the solution of ammonia ; the three glasses were connected together by pieces of amianthus (fibrous and silky asbestos). A power of 150 pairs was used. In less than five minutes it was found, by litmus paper [which is turned red by acids], that acid was collecting round the positive point ; in half an hour the result was sufficiently distinct for accurate examination. The water was sour to the taste, and pre- cipitated a solution of nitrate of baryta ; muriatic acid from muriate of soda, and nitric acid from nitrate of potash were transmitted through concentrated alkaline menstrua under similar circumstances ; when distilled water was placed in the negative part of the circuit, a solution of sulphuric, muriatic, or nitric acid in the middle, and any neutral salt with the base of lime, soda, potash, ammonia, or magnesia in the positive part, the alkaline matter was transmitted through the acid matter to the negative surface with similar cir- PEACTICAL ILLUSTKATIONS OF ELECTROLYTIC THEORY. 77 cumstances to those occurring during the passage of the acid through alkaline menstrua." Electrical Transfer of Elements. Sir H. Davy, in some of his experiments on the transference of elements from pole to pole of an electric circuit, employed vessels consisting of the substance to be decomposed. In one experiment, for example, two cups of sulphate of lime (gypsum) were filled with water and connected by means of moist cotton, one pole of the pile (Volta's pile being the source of electricity) was placed in each cup, and soon after it was found that the negative cup contained a solution of lime, and the positive cup a solution of sulphuric acid. A very striking illustration of the transfer of elements under the decomposing influence of the electric current is shown in the decom- position of chloride of silver (a compound of chlorine and silver) when two silver wires are employed as the electrodes. If a small quantity of the chloride be fused upon a piece of glass, and the two poles placed in contact with it, metallic silver is abundantly deposited at the negative electrode, while an equal quantity is dissolved from the positive wire. In this case the chlorine is not set free, but is engaged in dissolving the silver of the positive wire exactly in the proportion in which it is being deposited at the negative wire. If this latter electrode be carefully drawn from the fused globules as the silver is reduced there, and without interruption in its continuity, a wire or thread of reduced silver several inches in length may be produced. It will be necessary, however, while the silver is being dissolved from the positive wire, to keep it continually in contact with the fused mass and at a short distance from the negative wire. Practical Illustrations of the Electrolytic Theory. Suppose we take a solution of sulphate of copper, composed of 4 ounces of the sulphate dissolved in a quart of water, to which is added about 2 ounces of oil of vitriol. We next attach a piece of sheet copper, about 3 inches square, to the positive pole of a Smee or Daniell battery, and a plate of clean sheet-brass or German-silver of about the same dimensions to the negative pole, and immerse both plates in the copper solution : in a few moments we shall observe that the brass has become coated with copper. If the operation be allowed to pro- ceed undisturbed for a few hours, at the end of that time we shall find that a copper deposit of considerable thickness has taken place upon the brass plate, while the copper plate (the anode] has become greatly reduced in substance. If the two plates are weighed before and after the prolonged immersion, it will be found, on re -weighing them, that one plate (the copper) has lost what the other (the brass) has gained, while the copper solution will have preserved its equili- brium. In this experiment several important facts are elicited: 7 8 THEORY OF ELECTROLYSIS. I. That the metal is deposited upon the negative electrode. 2. That the positive electrode becomes dissolved. 3. That the copper is deposited direct from the solution on to the brass plate. 4. That the metallic strength of the solution is kept up by the gradual dissolving of the copper anode, which may be thus explained : the water of the solu- tion, being decomposed by the current, its oxygen is liberated at the positive (in this case copper) pole, when it combines with the metal, forming oxide of copper ; at the same time the sulphuric acid of the sulphate of copper is set free, and this, seizing the oxide of copper, forms sulphate of copper, which at once becomes dissolved in the solution. The hydrogen, liberated at the negative pole, does not escape in the form of gas, but, as it becomes released from the water, it takes the place of the copper removed from the solution during the process of electro-deposition. A very useful little apparatus for experimenting upon the electro - decomposition of liquids is represented in Fig. 50. It consists of a plate-glass cell, made by cementing five pieces of glass together with Fig. 50. transparent cement and supporting them upon a wooden stand, as in the engraving, upon which they are fastened with cement. The cell is about five or six inches long and two inches in width. The cell is divided into two compartments by inserting a temporary diaphragm (, Fig. 51), which is a small cane or wooden frame with muslin stretched over it. When this is put into its place, as at a, a separate electrode may be introduced into each of the compartments thus formed, and these may consist of two strips of thin platinum foil, or thin plates of carbon, about four inches long and half an inch in width. To illustrate the evolution of chlorine at the anode or positive pole, nearly fill the glass cell with a weak solution of salt-and-water, slightly acidulated with hydrochloric acid, and colour the solution blue with a few drops of a sulphuric solution of indigo. The electrodes are then introduced, when, in a few minutes, the solution in the anode compartment will be found to lose its colour and eventually become quite colourless, owing to the action of the chlorine disengaged at the anode, which has the power of bleaching the indigo. Another interesting experiment is to fill the glass cell with a weak PRACTICAL ILLUSTRATIONS OF ELECTROLYTIC THEORY. 7$ solution of starch, to which a little iodide of potassium must be added. When the current is passed through the solution the iodine will show itself at the anode by a beautiful blue colour, it being the peculiar property of this substance to strike a blue colour with starch, forming an iodide of starch. Lastly, if the cell be filled with a solution of common salt, to which a few drops of yellow prussiate of potash are added, and an iron, electrode introduced into each compartment, the division in which the anode or positive electrode is placed will assume a beautiful deep blue colour, while the solution in the other or negative compartment will remain colourless. The blue colour in the anode division is due to the oxidation of the iron and its solution by the prussiate of potash form- ing prussian Hue. CHAPTER VL ELECTRICAL THEORIES IN THEIR RELATION TO THE DEPOSITION OF METALS. Conductors and Insulators. Relative Conducting Powers of Metals. Defini- tion of Electrical Terms. Simple and compound Voltaic Circles. Resistance : Ohm's Law. Application of Ohm's Law to Compound Voltaic Circles. Electrical Units. Electromotive Force of Batteries. Electrolytic Classification of Elements. WHILE it would be beyond the province of the present work to enter deeply into theoretical considerations, it is necessary, in the present advanced state of electrical science, that both the student and practical operator should be acquainted with the principles and laws which govern the development of electricity that force or power with which he has to deal in all electrolytic operations. No matter how it may be obtained, whether it be generated by chemical or mechanical means, or by heat (as in thermo -piles), the " current " or force is, to the electro -metallurgist, what steam is to the engineer a means of doing a certain amount of work. When we take into consideration the many ways at present known of generating or bringing into action this subtle force, and the marvellous effects which it is capable of pro- ducing, it becomes at once apparent that if we desire to render this power subservient to practical purposes in the arts, we should know something of the principles which are involved in its production and influence its action, that we may be the better able to regulate or con- trol the current to suit the various purposes to which we desire to apply it. For a full knowledge of the laws of electrical science, the reader is referred to standard works on electricity, those mentioned in the footnote * being specially recommended. Conductors and Insulators. It is understood that all bodies are capable of conducting or transmitting electricity, though in very dif- ferent degrees, and that all substances insulate or resist the passage of the current also in different degrees. Faraday was of opinion that * ' The Student's Text-Book of Electricity," by H. M. Noad, Ph.D., F.R.S., Ac ; revised edition by W. H. Preece, M.I.C.E. ; and Fleeming Jenkin's " Treatise on Electricity and Magnetism." CONDUCTORS AND INSULATORS. Si conduction and insulation are only extreme degrees of one common condition ; that they are the same in principle and in action, except that in conduction an effect common to both is raised to the highest degree, whereas in insulation it occurs in the best cases only in an almost insensible quantity. In the following list the bodies are arranged in the order of their conducting power, silver being recog- nised as the best conductor, and ebonite the most perfect insulator. All the metals. Well-burnt charcoal. Plumbago. Concentrated acids. Powdered charcoal. Dilute acids. Saline solutions. Metallic ores. Animal fluids. Sea water. Spring water. Rain water. Ice above 13 Fahr. Snow. Living vegetables. Living animals. Flame smoke. Steam. Salts soluble in water. Rarefied air. Vapour of alcohol. Vapour of ether. Moist earth and stones. Powdered glass. Flowers of sulphur. Dry metallic oxides. Oils, the heaviest the best. Ashes of vegetables. Many transparent crystals. Dry ice below 13 Fahr. Phosphorus. Lime. Dry chalk. Native ca bonate of baryta. Lycopodium. Caoutchouc. Camphor. Siliceous and argillaceous stones. Dry marble. Porcelain. Dry vegetables. Baked wood. Leather. Parchment. Dry paper. Hair. Wool. Dried silk Bleached silk. Raw silk. Transparent gums. Diamond. Mica. All vitrifications. Glass. Jet. Wax. Sulphur. Resins. Amber. Gutta-percha. Shellac. Ebonite. The conductor commonly employed for conveying the current from voltaic batteries, and magneto and dynamo -electric machines to the depositing baths, as also for suspending the anodes and objects to be coated with metal, is copper, which, besides being the second best conductor, has the advantage of being comparatively cheap and readily 82 ELECTRICAL THEORIES. procurable, while its extreme pliability renders it easy to adapt to the various purposes of electro -deposition. The copper wire employed for transmitting the current from voltaic batteries of moderate dimensions may be from -fa to f inch in thickness, while the wire, or " cable " as it is sometimes called, used to connect powerful magneto and dynamo - electric machines with the depositing tanks is generally from half to one inch in diameter ; these leading wires are sometimes insulated by being covered with gutta-percha or other insulating material. Relative Conducting Power of Metals. The following table gives the relative conducting powers of pure metals and other conductors, according to Dr. Matthiessen : Silver . Copper . Gold . Zinc Cadmium Palladium Platinum Cobalt . Nickel . Tin 1 00*0 Thallium 99-9 Lead . 779 Arsenic . 29'O Antimony 23'7 Mercury 18-4 Bismuth 1 8-0 Graphite 17-2 Gas Coke 13-1 Bun sen's Coke 12-4 9-2 83 4-8 4-6 r6 1*2 06 9 038 025 It will thus be seen how nearly silver and copper approximate each other in conducting power, and how greatly the conductivity of metals diminishes after gold is reached. The conduction -resistance of liquids, as compared to metals, is enormous ; for example, if that of copper at 32 Fahr. equals i, those of the following liquids are Nitric acid at 55 Fahr 976,000 Sulphuric acid diluted to -rf at 68 Fahr. . . 1,032,020 Saturated solution of chloride of sodium at 56 Fahr. 2,903,538 sulphate of zinc . . . 15,861,267 sulphate of copper at 48 Fahr. 16,885,520 Distilled water at 59 Fahr 6,754,208,000 Definition of Electrical Terms. The late Professor T. Clark- Maxwell and Mr. Fleeming Jenkin, in their report " On Standard Electrical Resistances," as members of a committee appointed by the British Association,* adopted the following definitions of the terms electromotive force, resistance, current, and quantity, which are now generally accepted. Electromotive Force. By this term, which is frequently written Report, 1863. DEFINITION OF ELECTRICAL TERMS. 83 E.M.F., is to be understood that quality of a voltaic battery or other source of electricity, in virtue of which it tends to do work by the transfer of electricity from one point to another, and this force is measured by measuring- the work done during" the transfer of a given quantity of electricity between these two points. Dr. Joule proved that whether the work done be mechanical, chemical, or thermal, it is proportional to the square of the current, to the time during which it acts, and to the resistance of the circuit. The electromotive force is, in fact, the strength or power of the current to overcome resistance. The unit of electromotive force adopted in this country is termed a volt. Electrical Resistance. By this term is understood that quality of a conductor in which it prevents the performance of more than a certain amount of work in a given time by a given electromotive force. The resistance of a conductor is, therefore, inversely proportional to the work done in it when a given electromotive force is maintained between the two ends. The unit of resistance is termed an ohm. Electrical Current. By this term is meant the cause of the peculiar properties possessed by a conductor used to join the opposite poles of a voltaic battery ; namely, those of exerting a force on a magnet in its neighbourhood ; of decomposing certain compound bodies called electrolytes, when any part of the conductor is formed of such com- pound bodies ; or of producing currents in neighbouring conductors as they approach or recede from them. Quantity. The force with which one electrified body acts upon another at a constant distance, varies under different circumstances. "When the force between the two bodies, at this constant distance and separated by air, is observed to increase, it is said to be due to an increase in the quantity of electricity, and the quantity at any spot is defined as proportional to the force with which it acts through air on some other constant quantity at a distance. If two bodies charged with a given quantity of electricity are incorporated, the single body thus composed will be charged with the sum of the two quantities. Intensity. Mr. Latimer Clark pointed out* that the expression intensity, as ordinarily used, involves two perfectly distinct qualities, viz. : tension, or electromotive force, or electric potential, and quantity. All the most striking properties of electricity, such as the decomposition of water and salts, the combustion of metals, the deflection of the galvanometer, the attraction of the electro -magnet, and the physiolo- gical effects of the current are really dependent, as regards their magnitude and energy, solely on the quantity of electricity passing. Their greater energy, when the tension is increased, is an indirect effect due not to that tension, but to the increased quantity which * " Proceedings of the Royal Institution," March isth, 1861. 84 ELECTRICAL THEORIES. passes in a given time by reason of the increased tension. The unit of current strength is termed an ampere. Simple and Compound Voltaic Circles. In a simple voltaic circle or battery, in which the plates are large, the quantity of elec- tricity generated or set in motion is very considerable, while its intensity or power of overcoming resistance is low. The energy de- pends on the size of the plates, the intensity of the chemical action on the oxidisable metal, the rapidity of its oxidation and the speedy removal of the oxide. It is not, however, necessary that the plates composing a simple voltaic circle should consist of two opposed surfaces only ; the same electrical effect is obtained if the plates are cut up into a number of pieces and placed in different vessels, each contain- ing the same exciting fluid, provided the same extent of surface be preserved and the pieces be kept at the same distance apart. Thus, let a plate of platinum and another of amalgamated zinc, each four inches square, be immersed at a distance of one inch apart in dilute sulphuric acid, and connected by a stout copper wire ; after the lapse of a certain time a certain quantity of zinc will be dissolved, and a corresponding quantity of hydrogen gas will be evolved on the surface of the platinum ; now let each plate be cut into four strips, each i inch broad and 4 inches long, and let a pair of each metals be im- mersed, at a distance of one inch apart, in four separate vessels con- taining dilute sulphuric acid ; let all the platinum plates be connected together by a stout copper wire, and all the zinc plates by a similar wire, and let the two wires be united ; the same amount of zinc will be dissolved in the same time, and the same amount of hydrogen liberated, and the same quantity of electricity thrown into circulation, as with a single pair ; the four pairs and the single pair are equally simple voltaic circles. Noad. If, however, instead of uniting all the plates together in two sepa- rate groups, as above, we alternate the series by con- necting the zinc of one cell with the platinum of the next cell, and so on throughout the whole series, as in Fig. 52, by which arrangement a zinc plate will be at one end of the series, and a platinum plate at the other, the amount of zinc dissolved and hydrogen set free will be precisely the same as before, but the electromotive force is increased fourfold ; the re- sistances are at the same time still further increased, for while in the former arrangement a stratum of liquid 4 inches wide and I inch thick had to be traversed by the current, in the second arrangement it has to OHM'S LAW. 85 pass through 4 separate inches of liquid, each I inch in width. By this latter method of connecting the plates, however, there is a starting-point of power in each cell, whereby each contributes its energy in urging forward the current, and though the quantity of electricity is npt greater than when the plates were arranged as a single pair, its intensity (electromotive force) or power of overcoming resistance is greatly increased, and, within certain limits, this power is increased in proportion to the number of couples arranged in alternate series. This arrangement constitutes a compound voltaic circle, or compound battery. Resistance : Ohm's Law. Even under the most favourable con- ditions, it is well known that from a voltaic battery we never get a full equivalent of electrical power in return for the chemical action which takes place within the battery cell, and this loss of power is due to internal resistance within the battery itself, and this, as we have shown, is overcome when several cells are connected in alternate series, that is the zinc of one cell with the copper of the next, and so on throughout the series. External resistance is that which opposes the current in the conducting wires, the electrolyte, or other body employed to complete the circuit. A current which is not much affected by external resistance is said to possess considerable electro- motive force, or in other words is of " high intensity." We are indebted to Professor Ohm, of Nuremberg, for an exposition of the causes which influence the quantity of electricity obtained in a voltaic circuit, who investigated the subject mathematically, and his formulae have been verified experimentally by Daniell, "Wheatstone, and others, and are regarded as the basis on which all other investi- gations that have since been made relative to the force of the current are founded. Ohm's law may be thus briefly defined : the strength or force of the current is equal to the electromotive force divided by the resistance in the circuit ; thus, if we take c to denote the actual strength of the current, that is its power to produce heat, magnetism, chemical action, &c., E the electromotive force, and E the resistance of the wires and electrolytes, then _ Ohm's law may also be explained as follows : 1. The volume or strength of the current in any circuit is found by dividing the value of the E.M.F. (as measured by the difference of potential existing in the circuit) by the value of its total resist- ance. 2. The resistance in any circuit is found by dividing the value of the E.M.F by the value of the current. 86 ELECTRICAL THEORIES. 3. The E.M.F. in any circuit is found by multiplying the value of the resistance contained in it by the value of the current traversing it. 4. The quantity of electricity produced in any circuit is found by multiplying the value of the current by the time during which the current flows. The term quantity in its proper significance refers solely to static and not to dynamic electricity, although the duration of the dynamic effect depends upon the quantity originally present. When the conductor or storage battery is discharged, by joining its poles to a conductor, the conductor is traversed by the current. If the conductor has a great resistance, it will require considerable time for the whole to pass, and thus the current will be a comparatively weak one. If, on the other hand, the resistance of the conductor is small, the whole quantity will pass in a much shorter time, and the current will be a much stronger one. If we increase the number of elements of a voltaic battery, arranging them in alternate series, we increase the tension, urging the electricity forward, but at the same time we increase the amount of resistance offered by the liquid portion of the circuit ; so that, pro- vided in both cases the circuit be completed by a competent conductor, such as a stout copper wire, we obtain the same results in both cases, the electromotive forces and the resistances being increased by an equal amount. The resistance includes the resistance of the con- ducting wires, the electrolyte, and the resistance of the liquid and elements of the battery itself. The resistance of the battery is found to decrease in exact proportion as the surface is increased, and the resistance of the wire is directly as its length, and inversely propor- tional to its section. Application of Ohm's Law to Compound Voltaic Circles. Since each pair of elements of a voltaic battery contributes its own E.M.F. to the current, it foUows that the whole E.M.F. will be proportional to the number of pairs, provided they are all equal. The following general law has been established by Wheatstone : 1. The electromotive force of a voltaic current varies with the number of the elements and with the nature of the metals and liquids which constitute each element, but is in no degree dependent on the dimensions of any of their parts. 2. The resistance of each element is directly proportional to the distances of the plates from each other in the liquid, and to the specific resistance of the liquid, and is also inversely proportional to the surface of the plates in contact with the liquid. 3. The resistance of the connecting wire of the circuit is directly proportional to its length and to its specific resistance, and inversely proportional to its section. ELECTRICAL UNITS. The resistances of different metals are inversely as their conducting powers, and their conductivity is greatly influenced by temperature, as will be seen in the following table by Dr. Matthiessen : Metal Pure. Conductivity. Conductivity at 212. Silver at 32 = 100. Silver at 2I2 = IOO. Each metal com- pared with itself at 32= ion. Silver (hard drawn) . . Copper (hard drawn) . . Gold (hard drawn) . . . Zinc At 32 lOO'OO 99'95 77-96 29'02 23'72 I7-22 16-81 13'n 12-36 9'i6 8-32 4-76 4-62 1-245 At 21 2 7i - 56 70-27 55-90 20-67 16-77 8-67 ?86 333 3-26 0-878 lOO'OO 98-20 78-11 28-89 23-44 I2'I2 8'i8 4-6 5 4'55 1*227 7i'56 70-31 71-70 71-23 70-70 70" 1 1 68-58 70-39 69-88 70-54 70-51 Loss p. c. 28-44 29-69 28-30 28-77 29-30 29-89 3I-42 29-61 30" 1 2 29-46 29-69 Cadmium . . Cobalt Iron (hard drawn) . . . Nickel Tin Thallium .... Lead Arsenicum Antimonj 7 Electrical Units. There has been much diversity amongst English and Continental electricians as to the best system of electrical measure- ment to be founded on the various theories of Ohm, Weber, Thomson, Ampere, and others ; but we may take it as a general rule that in this country the Volt is accepted as the unit of electromotive force, the Ohm, the unit of resistance, and the Ampere, the unit of quantity, or current strength, which determines the amount of electric work done in a given time. In estimating the electric power of a dynamo- electric machine or battery, its electromotive force is taken in volts, its resistance in ohms, and its quantity or strength is determined in amperes. For these purposes certain measuring instruments are employed, termed voltmeters and ammeters respectively, of which there are many different forms in use. One of the most delicate and reliable instruments for measuring the current is Siemens' dynamometer ; but for workshop uses those instruments which are enclosed in a lacquered brass, or a wooden case, are to be preferred. The volt is also called the unit of potential, and does not differ greatly from the potential which normally exists between the poles of a single sulphate of copper cell (being about 95 per cent, of it), and for approximate calculations may be considered equivalent to it. In 88 ELECTRICAL THEORIES. other words, a Daniel! cell is a little more than a volt, the determina- tions of it value by different experimentalists being as below : Werner Siemens Latimer Clark . Sir W. Thomson F. Kolrausch rio6 volt, i '079 Electromotive Force of Batteries. The following table, after Ferrini, gives the E.M.F. of various batteries, in volts, and will be very useful for reference : TABLE OF ELECTROMOTIVE FORCE OF BATTERIES. Name ot Element. Constitution. Electro- motive Force in Volts. Authority. Wollaston . . Amalgamated zinc ancH 0-886 Clark and Sabine. copper in dilute sul- > 0*861 Sprague. phuric acid (1:12) J 0719 De la Rive. Smee .... Amalgamated zinc in ) sulphuric acid, plati- nised silver, or plati- } num in sulphuric acid (i : 12) J i 1-098 1-107 0-54I 1-192 Clark and Sabine. Sprague. De la Rive. Naclari. Daniell . . .< Amalgamated zinc in^ sulphuric acid (1:4); copper in saturated so- > lution of copper sul- phate J 1-079 1-079 1-079 1-079 Clark and Sabine. Sprague. De la Rive. Naclari. Zinc in dilute sulphuric" acid (i : 12); "copper in saturated solution 0-978 i 0-98 Clark and Sabine. Du Moncel. - Zinc in sal-ammoniac;' 1-481 Clark and Sabine. carbon with manganese 1*561 Sprague. peroxide in sal-ammo- 1-942 De la Rive. Leclanche . . niac Zinc in solution of com-") mon salt ; carbon with i manganese peroxide in f common salt solution J 1-259 i '493 1-360 i '34 Beetz. Sprague. Naclari. Du Moncel. Marie-Davey . Zinc in dilute sulphuric f acid (i : 12) ; carbon { in mercurous sulphate 1 i '524 i '542 1-482 1-440 Clark and Sabine. Sprague. Naclari. Du Moncel. Zinc in dilute sulphuric^) acid (i : 12); platinum > i'956 Clark and Sabine. in fuming nitric acid i Grove. . . .< Zinc in dilute sulphuric ] acid (i : 12); platinum I i '524 Clark and Sabine, in nitric acid of 1-38 f I *542 Sprague. sp. gr. ELECTBOLYTIC CLASSIFICATION OF ELEMENTS. 89 TABLE OF ELECTROMOTIVE FORCE (continued}. Name of Element. Constitution. Electro- motive Force in Volts. Authority. f Zinc in dilute sulphuric^ acid (i : 12); carbon V in fuming nitric acid J 1-964 i '95 Clark and Sabine. Du Moncel. Bunsen . . . j Zinc in dilute sulphuric "j acid (i : 12) ; carbon i in nitric acid of 1-38 f 1-888 1-941 1-880 Clark and Sabine. Beetz. Naclari. sp. gr. J Zinc in dilute sulphuric") acid (i : 12) ; carbon ', in bichromate of potas- f sium J 2-028 1-905 2'120 Clark and Sabine. Sprague. Naclari. Grenet . . . Zinc and carbon in bi-\ Nflolnr? chromate of potassium / 25 i> aciari. Electrolytic Classification of Elements. The following table indicates the electric relations of simple or elementary bodies to each other, but is subject to modifications, and indeed reversal of order, according to the nature of the exciting fluid in which the pairs of elements may be immersed. The list will, however, prove useful as a general guide. In the first column of negative bodies, each element is to be considered negative to all below, and positive to all above it, and the same applies to the second column of positive bodies. The elements are therefore negative or positive only in relation to each other ; as an example, if a compound of oxygen and chlorine be electrolysed, the former would go to the positive and the chlorine to the negative electrode ; if the compound were composed of chlorine and phosphorus, the chlorine would then go to the positive, and the phosphorus to the negative pole : Electro-negative Elements. Oxygen. Sulphur. Selenium. Nitrogen. Fluorine. Chlorine. Bromine. Iodine. Phosphorus. Arsenic. Chromium. Vanadium. Electro-positive Elements. Potassium, Sodium. Lithium. Barium. Strontium. Calcium. Magnesium. Aluminium. Uranium. Manganese. Zinc. Iron. 9 o ELECTRICAL THEORIES. Electro-negative Elements. Tungsten. Boron. Carbon. Antimony. Tellurium. Titanium. Silicon. Hydrogen. Electro-positive Elements. Nickel. Cobalt. Cadmium. Lead. Tin. Bismuth. Copper. Silver. Mercury. Palladium. Platinum. Gold. In the foregoing pages we have briefly dwelt upon such theoretical considerations as are more directly connected with the principles of electrolysis explained in the previous chapter ; for a more intimate acquaintance with the principles of voltaic and dynamic electricity, we must again refer the reader to Noad's " Text-Book of Electricity," .Fleeming Jenkins' " Electricity and Magnetism," and the numerous other treatises upon electrical science of recent date. CHAPTER VII. ELECTRO-DEPOSITION OF COPPER. Electrotyping by Single-cell Process. Copying Coins and Medals. Mould- ing Materials. Gutta-percha. Plastic Gutta-percha. Gutta-percha and Marine Glue. Beeswax. Sealing-wax. Stearine. Stearic Acid. Fusible Metal. Elastic Moulding Material. Plaster of Paris. IT may fairly be said that the discovery of the electrotype pro- cess formed the basis of the whole electrolytic industry ; and, in its applications to various purposes of the arts and to literature, it has proved of inestimable value. While, in its infancy, the electro- type process was a source of scientific recreation to thousands of persons of all classes, many were those who saw in the new process a wide field of research, from which much was expected and more has been realised. While Faraday, Becquerel and others were investi- gating the process in its more scientific relations, practical men were trying to apply it to various art purposes, until, in course of time, electrotyping was added to our list of chemical arts. The simplest form of arrangement for electrotyping small objects is known as the " single -cell " process, which it will be well to con- sider before describing the moue elaborate apparatus employed for larger work. Electrotyping by the Single -cell Process. In its most simple form, a small jar, Fig. 53, may be used as the outer vessel, and in this is placed a small porous cell, made of unglazed earthenware or biscuit porcelain, some- what taller than the containing vessel. A strip of stout sheet-zinc, with a piece of copper wire attached, either by means of solder or by a proper binding screw, is placed in the porous cell. A saturated solu- tion of sulphate of copper (bluestone), made by dissolving crystals of that substance in hot water, Fig. 53. and pouring the liquid, when cold, into the outer cell. The porous cell is then filled to the same height as the copper solution with a solution of sal-ammoniac or common salt. To keep up the strength of the solution when in use a few crystals of sulphate of copper are placed in a muslin bag, which is hooked on to the ELECTKO-DEPOSITION OF COPPER. edge of the vessel by means of a short copper hook, and the bag allowed to dip a little way into the liquid. The prepared mould is connected to the end of the wire (which is bent in this fj form) and gently lowered into the solution, when the whole arrangement is complete. In place of the porous cell the zinc may be wrapped in several folds of brown paper, enclosing a little common salt, but the porous cells are so readily obtained that it is never worth while to seek a substitute for them. This simple arrangement will easily be understood by referring to the cut. A more convenient single -cell apparatus is shown in Fig. 54, in which the containing vessel, or cell, is a glass or stoneware jar capable of holding about three pints. In this is placed a porous cell (p ) . A bar or plate of zinc (z), with binding screw attached, is de- posited in the porous cell ; a short piece of copper wire (w), for suspending the mould (m] or object to be copied, has its shorter end inserted in the hole of the binding- screw. The outer vessel is about three parts filled with a saturated solution of sul- phate of copper (c), and the porous cell is filled to the same height with a half -saturated solution of sal-ammoniac or common salt. If the zinc is amalgamated, however, dilute sulphuric acid is used instead of the latter solution in the porous cell, and a small quantity of oil of vitriol (from half an Fig. 54- ounce to one ounce of acid to the quart of copper solution) added. Amalgamating the Zinc. Pour a little dilute sulphuric acid, or un- diluted muriatic acid, into a dish, and, having tied a piece of flannel to the end of a stick, lay the zinc in the dish and proceed to brush the acid all over the plate ; now pour a little mercury (quicksilver) on the plate, and rub it over the zinc with the little mop, when it will readily spread all over the surface, giving the zinc a bright silvery lustre. It is important that the zinc should be thoroughly cleaned by the acid, otherwise the mercury will fail to amalgamate with the metal, and dark patches of unamalgamated zinc will appear. The perforated shelf, or tray, in the engraving is a receptacle for crystals of sulphate of copper, which, being placed upon it, gradually become dissolved while the deposit of copper is going on, and thus re-supply the solution as it becomes exhausted, whereby the operation progresses uniformly. To prepare the copper solution for small experimental purposes, dissolve about 10 ounces of sulphate of copper in I quart of hot water and stir until the crystals are all dissolved ; then set the vessel aside until cold, when the clear liquor is to be carefully poured into COPYING COINS AND MEDALS. 93 the depositing cell. When unamalgamated zinc is used in the single- cell arrangement the sulphate of copper should be simply a saturated solution of the salt without that addition of acid, though a few drops only may be added with advantage. It is of great importance that the sulphate of copper should be pure. The crystals should be of a rich dark blue colour and absolutely free from greenish crystals (sulphate of iron], which not unfrequently get mixed with the copper salt by the carelessness of the shopkeepers' assistants. Copying Coins and Medals. Before explaining the various methods of obtaining moulds from different objects, for the purpose of producing fac- similes in copper, let us see how we may employ the above apparatus in a more direct way. Suppose we desire to obtain a copy, in reverse, of some medal or old coin, or even a bronze penny- piece, having decided which side of the coin it is intended to electro- type say the obverse or "head" side we must first render the surface clean and bright. This may be very readily done by means of rottenstone and a little olive oil, applied with a piece of chamois leather and briskly rubbed over the face of the coin. In two or three minutes the surface will be sufficiently bright, when the oil must be wiped off thoroughly either with cotton wool or blotting paper. A short piece of copper wire is next to be soldered to the back of the coin, and the polished side is then to be brushed over with a soft plate- brush and plumbago, or blacklead, which will prevent the deposited copper from adhering to the medal. In order to prevent the copper from being deposited upon the back and rim these parts must be coated with some non-conducting material. For this purpose paraffin wax, applied by gently heating the medal and touching it with the wax, or red sealing-wax, dissolved in spirit of wine or wood spirit (pyroxylic spirit), brushed over the surfaces to be protected, will answer well ; but if the latter is employed it must become thoroughly dry before being placed in the copper solution. Being thus prepared, the end of the conducting wire is to be in- serted in the binding screw attached to the zinc and securely fixed by turning the screw until it grips the wire firmly. The coin must be lowered into the solution steadily, with its face towards the porous cell, and if any air-bubbles appear upon its face they must be re- moved by means of a camel-hair brush, or, still better, by blowing upon them through a glass tube. It is a good plan to breathe upon the face of the coin before placing it in the solution, which, by cover- ing it with a layer of moisture, effectually prevents the formation of air-bubbles. In about twenty-four hours from the first immersion of the medal the deposit of copper will generally be sufficiently stout to bear re- 94 ELECTEO-DEPOSITION OP COPPEK. moving from the original, when the extraneous copper, which has spread round the edge of the deposit, or electrotype, may be carefully broken away by means of small pliers ; if the medal be gently heated over a small lamp, the electrotype will readily become detached, and will present, in reverse, a perfect copy of the original, in which even the very finest lines will be accurately reproduced. In its present condition the electrotype is hard and brittle, and will, there- fore, require careful handling. To give it the toughness and flexi- bility of rolled copper it is only necessary to heat the electrotype to dull redness, which may be conveniently done by placing it on a piece of sheet-iron, and laying this on the clear part of a fire until red hot, when it must be withdrawn and the " type" set aside to cool. If placed in a very weak solution of sulphuric acid for a few moments, then rinsed and dried, and afterwards brushed over with a little rouge or whiting, its surface may be readily brightened. If we desire to obtain a copy in relief from our electrotype (also in copper) we must now treat it as the mould, following the same routine as before in all respects, by which we shall obtain a perfect fac- simile of the original coin, which may be mounted and bronzed by any of the processes hereafter given. Having thus seen what results may be obtained with the most simple application of the single-cell process, we will next turn our at- tention to the different methods of obtaining moulds from various objects, but, before doing so, it will be necessary to consider the nature of the several substances which are employed in moulding and the methods of preparing them for use. Moulding Materials. The chief substances used in the electro - typing art for making moulds are gutta-percha, wax, and fusible metal ; other materials, however, are employed in certain cases in which the substances named would be inapplicable. The various materials will be considered under their separate heads, as follows : Gutta-percha. This most useful moulding material is the concrete juice of Isonandra Gutta, a tree growing only in the Malayan Archi- pelago, and of other species of the same genus. The stem of the gutta-percha tree, which sometimes acquires the diameter of 5 or 6 feet, after being notched yields a milky juice which, when ex- posed to the air for some time, solidifies, and this constitutes the gutta-percha of commerce. As imported, it is in irregular blocks of some pounds in weight, and commonly containing a large proportion of impurities in the shape of bark, wood, stones, and earthy matter. To purify the crude article it is first cut in thin slices, which are after- wards torn into shreds by machinery. These are next softened by hot water and afterwards kneaded in a masticator, by which the im- purities become gradually washed away by the water. After several MOULDING MATERIALS. 95 hours the gutta-percha is found to be kneaded into a perfectly homo- geneous mass, which is rolled or drawn into sheets, bands, &c. Gutta-percha becomes soft and plastic at the temperature of boiling water (212 Fahr.), when two pieces may be welded together. It is a non-conductor of electricity, and is indeed one of the best insulating materials known ; it is impervious to moisture, and is scarcely at all affected by either acids or alkalies. Owing to its plasticity when soft, it is one of the most useful materials for making moulds, yielding im- pressions which are exquisitely sharp in the very finest lines. When used for making moulds from small objects, as coins, medallions, or sealing-wax impressions of seals, a piece of gutta-percha of the re- quired size is placed in hot water (the temperature of which should be about 1 60 Fahr.), and, when sufficiently soft, it should be rolled while still wet in the palms of the hands until it assumes the form of a ball ; it should then again be soaked in the hot water for a short time, and be again rolled as before, care being taken to observe that the surface of the ball exhibits no seams or fissures. When larger objects have to be copied stout sheet gutta-percha is used, and a piece pf the required size cut from the sheet, which is softened as before, then applied to the object, and the necessary pressure given to secure a faithful impression. Plastic Gutta-percha. When gutta-percha is steeped for a few hours in benzol or naphtha it becomes considerably swollen ; if afteV wards soaked in hot water it is exceedingly plastic, and requires but moderate pressure to obtain most perfect copies from even such fragile objects as plaster of Paris models. Gutta-percha and Marine Glue. The following has also been recommended : gutta-percha 2 parts, Jeffrey's marine glue i part. Each of the materials is first to be cut up into thin strips ; they are then to be mixed, placed in a pipkin and heated gently, with con- tinual stirring, until the substances have become well incorporated : the mixture is now ready for use, and should be rolled into the form of balls before being applied for taking impressions. A very useful mixture is made by melting thin strips of gutta-percha as before, and adding one-third part of lard, keeping the mixture well stirred. It is applied by pouring it over flat surfaces, as steel plates, &c. Beeswax. This is a very useful material for moulding, and may be applied either in the form of virgin or white wax, or the ordinary commercial article yellow beeswax. Since this substance, however, is very commonly adulterated, it may be useful to know something of its natural characteristics. At the temperature of 32 Fahr. beeswax becomes brittle, at from 80 to 90 it becomes soft and plastic, and it melts at about 155 Fahr. Mr. B. S. Proctor says: "It becomes plastic or kneadable at about 85 Fahr. , and its behaviour while worked 96 ELECTRO-DEPOSITION OF COPPER. between the finger and thumb is characteristic. A piece the size of a pea being worked in the hand till tough with the warmth, then placed upon the thumb and forcibly stroked down with the forefinger, curls up, following the finger, and is marked by it with longitudinal streaks." Its ordinary adulterants are resin, farina, mutton suet, and stearine, though more ponderous substances, such as plaster of Paris, have sometimes been detected. White wax is very commonly adulterated with spermaceti, sometimes to the extent of two -thirds of the latter to one of wax. These sophistications, although not neces- sarily fatal to the preparation of good moulds, are certainly objection- able, inasmuch as it not unfrequently happens that a wax mould splits or cracks, not alone from cooling too quickly, but owing to the presence of foreign substances which impair its toughness. Sealing-wax. This substance may be employed for taking impres- sions of seals or crests, and was, indeed, one of the first materials used in the earliest days of electrotyping. The material, however, should be of good quality, and only sufficient heat applied to melt, without inflaming it. Stearine. Stearic Acid. The former substance is the solid con- stituent of tallow, and the latter (stearic acid) is the same substance separated from fats by chemical processes. Either may be used for making moulds instead of wax ; but the late C. V. Walker recom- mended the following mixture in preference to either : ozs. Spermaceti 8 Wax i| Mutton Suet if Another formula consists of : ozs. White Wax 8 Stearine 3 Flake White or Litharge i The whole ingredients are put into a pipkin and gently heated over a low fire, with continual stirring, for about half an hour, after which the mixture is allowed to rest until the excess of litharge (oxide of lead) has deposited. The clear residue is then to be poured into a shallow dish, and when cold is put aside until required for use. Fusible Metal. This alloy, which melts at the temperature of boiling water, and in some preparations very much below that point, is very useful for making moulds from metallic and some other objects ; and since it can be used over and over again, and is capable of yielding exceedingly sharp impressions, it may be considered one of the most serviceable materials employed for such purposes. The following ELASTIC MOULDING MATERIAL. 97 represent the principal formulae for fusible metal, the last of which melts at the low temperature of 151 Fahr. or 61 below the boiling- point of water : ozs. ozs. ozs. I. Bismuth . 8 II. Bismuth . 8 III. Bismuth 8 Lead . 4 Lead . 5 Lead . 4 Tin .* 4 Tin . 4 Tin . 2 Antimony i Cadmium 2 16 18 16 The metals are to be put into a crucible or clean iron ladle, and melted over a low fire ; when thoroughly fused, the alloy is poured out upon a cold surface in small buttons or drops, and these, when cold, are to be again melted and poured out as before, the operations to be repeated several times in order to ensure a perfect admixture of the metals. Another and better plan is to granulate the metal, or reduce it to small grains in the following way : Fill a tall jar or other vessel with cold water, and on the surface of the water place a little chopped straw (about 3 inches in length). When the metal is melted, get an assistant to stir the water briskly in one direction, then pour in the metal, holding the ladle at some distance from the surface of the water ; by this means the metal will be diffused and separated into a considerable number of small grains. The water is then to be poured off, and the grains collected, dried, and re -melted, after which another melting and granulation may be effected, and the alloy finally melted and cast into a mould, or simply poured out upon a flat iron or other surface, when it will be ready for future use. By the repeated melting, the alloy loses a little by the oxidation of the metals ; but since the heat required to fuse it is less than that of boiling water, the loss is but trifling, as compared with the importance of obtaining a perfect alloy of the various metals. It should be the practice to remove the crucible or ladle from the fire the moment the alloy begins to melt, and to depend upon the heat of the vessel to complete the fusion. Elastic Moulding Material. For making moulds from objects which are much under cut, in which case neither of the foregoing sub- stances would be available, an elastic material is employed which has the same composition as that from which printers' rollers are made, that is to say, a mixture of glue and treacle, the formula for which is: ozs. Glue of the best quality . .12 Treacle . 3 98 ELECTRO-DEPOSITION OF COPPER. The glue is first to be covered with cold water and allowed to stand for at least twelve hours, by which time it should be perfetly soft throughout. The excess of water is then to be poured off, and the vessel placed in a saucepan or other convenient utensil, containing a little water, and heat applied until the glue is completely melted, which may be aided by frequent stirring. When quite melted, pour in the treacle, and again stir until perfect incorporation of the ingredients is effected, when the composition may be set aside to cool until required for use. To check evaporation and consequent drying of the surface, the vessel, when the material is quite cold, may be inverted over a piece of clean paper, by which, also, it will be pro- tected from dust. The compound thus formed is exceedingly elastic, and may readily be separated from models even when severely undercut. Owing to the solubility of this composition, however, some care is necessary in using it, otherwise it will become partially dis- solved in the copper solution or both. This is more likely to occur, however, when the solutions are of less strength than saturated, by which term we understand that the water present holds as much sulphate of copper in solution as it is capable of doing. Various remedies for overcoming this disadvantage will be given when treating of the methods of obtaining moulds from the material. Plaster of Paris. This substance is also used for mould -making, either from metallic or natural objects ; but the plaster should be of the finest quality, such as is used by Italian image makers for the surface of their work, and not the coarse material usually sold in the shops. The plaster should be fresh when purchased and preserved in a closely- covered jar until required for use. Having thus far considered the materials used in making moulds for electrotype purposes, we will next explain the methods of applying them, confining our observations to the more simple examples in the initial stages of the process. CHAPTER VIII. ELECTRO -DEPOSITION OF COPPER (continued). Moulding in Gutta-percha. Plumbagoing the Mould. Treatment of the Electrotype. Bronzing the Electrotype. Moulds of Sealing-wax. Copying Plaster of Paris Medallions. Preparing the Mould. Plumba- going. Clearing the Mould. Wax Moulds from Plaster Medallions. Moulds from Fusible Metal. moulding in Gutta-percha. In the former case, we explained how a copy of a coin could be obtained, in reverse, by making the original act as the mould. We will now turn our attention to obtaining fac- simile duplicates in relief , from impressions or moulds of similar objects, from such of the materials described in the last chapter as will best answer the purpose ; and since the application of these materials in the simple way we shall indicate will lead to an understanding of the general principles of mould -making, it is recommended that the student should endeavour to acquire adroitness, in taking impressions which will be perfectly sharp and clear, before he attempts to obtain metallic deposits of copper upon them. To obtain a copy of a medal, coin, or other similar object, the most convenient material to employ is gutta-percha. Take a small piece of this substance and place it in hot but not boiling water for a few minutes, or until it is perfectly soft ; while still wet, roll it between the palms of the hands until it assumes the form of a ball ; it should then be replaced in the water for a short time, and again rolled as before. The coin to "be copied is now to be laid, face upward, upon a piece of plate-glass, slate, or polished wood. Now take the ball of gutta-percha and place it in the centre of the coin, and press it firmly all over it, from the centre to its circumference, so as to exclude the air, and in doing this it may be necessary to occasionally moisten the tips of the fingers with the tongue to prevent the gutta-percha from sticking to them. A flat piece of wood may now be laid over the gutta-percha, and if this be pressed forcibly by the hands this will ensure a perfect impression. After about a quarter of an hour or so, the gutta-percha mould may be readily removed from the coin, pro- vided that the material has set hard. Plumbagoing the Mould. Having thus obtained a mould from a IOO ELECTRO-DEPOSITION OF COPPER. material which is a non-conductor of electricity, we next proceed to give it a conducting surface, without which it would be incapable of receiving the metallic deposit of copper which constitutes an electro- type. For this purpose, phimbago, or graphite,* is usually employed. To plumbago the surface of the gutta-percha mould proceed as follows : Hold the mould between the fingers of the left hand, face upwards ; now dip a soft camel-hair brush in finely -powdered plum- bago (which should be of good quality) and briskly brush it all over the surface, every now and then taking up a fresh supply of plumbago with the brush. Care must be taken to well brush the powder into every crevice of the impression, and it is better to work the brush in circles, rather than to and fro, by which a more perfect coating is obtained. When properly done, the face of the mould has a bright metallic lustre, resembling a well-polished (that is blackleaded) stove. In order to prevent the deposit f each equal parts. Alum . ) These substances are placed in an earthenware pipkin, and melted at about the temperature of boiling water. When fused, the mixture is ready for use. The articles are to be brushed over with the com- FRENCH GILDING. 163 position, and are then placed in a charcoal furnace in which the fuel burns between the sides and a vertical and cylindrical grate, as shown in Figs. 723)- The work is placed in the hollow central por- tion where the heat radiates. A vertical section of the furnace is shown in Fig. 73. When put into the furnace, the salts upon the articles first begin to dry, after which they fuse, and acquire a dull, yellowish-red colour. On applying the moistened tip of the finger to one of the pieces, if a slight hissing sound is heard, this indicates that the heat has been sufficient, when the articles are at once removed and thrown briskly into a very weak sulphuric acid pickle, which in a short time dissolves the salts, leaving the work clear and bright, and of a fine gold colour. It must be borne in mind that this " colouring" process has a rather severe action upon gilt work, and should the gild- ing be a mere film, or the articles only gilt in parts, the fused salts will inevitably act upon the copper of which the articles are made, and strip the greater portion of the gold from the surface ; as it would be a great risk to submit a large number of in- differently gilt articles to the colouring process unless it was known that sufficient gold had been deposited upon them, although of inferior colour, it would be better to operate upon one or two samples first, when, if the result prove satisfactory, the bulk of them may then be treated as above. Some operators, when the Fig. 72. Fig- 73- " dipping " has not been satisfactory as to colour, give the articles a momentary gilding with the battery in the usual way. When it is desired to gild articles strongly by the dipping process, they are gilt several different times, being passed through a solution of nitrate of mercury previous to each immersion ; the film of mercury thus deposited on the work becomes dissolved in the pyrophosphate bath, being replaced by the subsequent layer of gold. In this way articles may be made to receive a substantial coating of gold. In France, large articles, such as clocks, ornamental bronzes, &c., are gilt in this manner, by which they acquire the beautiful colour for which French clocks and goods of a similar character are so justly famed. Boseleur states that he has succeeded in gilding copper by this method sufficiently strong to resist the action of nitric acid for several hours. When articles are strongly gilt by the dipping process, 164 DEPOSITION OF GOLD BY SIMPLE IMMERSION. they may be scratch-brushed, or subjected to the process called or-mouluing described in another place. Gilding Silver by Dipping, or Simple Immersion. The articles are first cleaned and scratch-brushed, after which they are boiled for about half an hour in the pyrophosphate gilding bath, to which a few extra drops of prussic acid or sulphurous acid have been added. The former acid dissolves a small portion of silver from the articles, which is replaced by an equivalent proportion of gold, while the sulphurous acid acts as a reducing agent in the gold solution, and causes the metal to deposit upon the silver from the affinity existing between the two metals, especially when one of them is in the nascent state, that is, just disengaged from a combination. This gilding is very fine, but with- out firmness. The deposit is rendered more rapid and thicker when the articles of silver are continually stirred with a rod of copper, zinc, or brass. Roseleur. The deposition by contact of other metals, is, how- ever, due to voltaic action set up by the pyrophosphate solution, and is altogether different to the action which takes place during the simple dipping process, in which a portion of the metal of which the article is composed is dissolved by the solution, and replaced by an equivalent proportion of gold. Preparation of the Work for Gilding As a rule, the articles should first be placed in a hot solution of caustic potash for a short time, to remove greasy matter, then well rinsed, and afterwards either scratch -brushed, or dipped in aqua fortis or " dipping acid" for an instant, and then thoroughly well rinsed. If the articles merely require to be brightened by scratch-brushing, after being gilt, it is only necessary to put them through the same process before gilding, which imparts to the work a surface which is highly favourable to the reception of the deposit, and which readily acquires the necessary brightness at the scratch-brush lathe as a finish. Articles which are to be left with a dead or frosted surface, must be dipped in dipping acid and rinsed before being placed in the gilding bath. It is com- monly the practice to " quick " the articles, after dipping in acid, by immersing them in a solution of nitrate of mercury until they become white ; after this dip, they are rinsed, and at once put into the bath. Gilding by Contact with Zinc Steele's Process. In this process, a solution is made by adding chloride of gold to a solution of cyanide of potassium : in this the articles to be gilt are placed, in contact with a piece of zinc, which sets up electro -chemical action, by which the gold becomes deposited upon the articles ; but since the metal also becomes reduced upon the zinc, the process would not be one to re- commend on the score of economy. In some cases, however, in which it is necessary to deposit a film of gold upon some portion of an article which has stripped in the burnishing, a cyanide solution of gold may be dropped on the spot, and this touched by a zinc wire, when it will GILDING WITH THE RAG. 165 receive a slight coating of gold, and thus save the necessity of re- gilding the whole article. This system of " doctoring " is sometimes necessary, but should be avoided if possible, as it is undoubtedly a fraud upon the customer, since the doctored spot must, sooner or later, yield up its film of gold and lay bare the metal beneath. Gilding with the Rag. This old-fashioned process, which was at one time much used for gilding the insides of snuff-boxes, bowls of mustard and salt spoons, &c., is conducted as below. Instead of forming the chloride of gold in the ordinary way, the following in- gredients are taken : Nitric acid ..... 5 parte. Sal-ammoniac (chloride of ammonium) . . 2 Saltpetre (nitrate of potassa) . . . . i A quantity of finely rolled gold is placed in a glass flask, and the other substances are then introduced ; the flask is next heated over a sand-bath. During the action which takes place, the nitric acid de- composes the chloride of ammonium, liberating hydrochloric acid, which combines with the nitric acid, forming aqua regia, which dis- solves the gold, forming chloride ; the nitrate of potash remains mixed with the chloride of gold. The flask is then set aside to cool : when cold, the contents of the flask are poured into a flat -bottomed dish, and pieces of linen rag, cut into convenient squares, are laid one above another in the solution, being pressed with a glass rod, so that they may become thoroughly impregnated with the liquid. The squares of rag are next taken up, one by one, and carefully drained, after which they are hung up in a dark closet to dry. When nearly dry, each piece of rag, supported upon glass rods, is placed over a charcoal fire until it becomes ignited and burnt to tinder, which is promoted by the nitrate of potash ; the burning rag is laid upon a marble slab until the combustion is complete, when the ashes are to be rubbed with a muller, which reduces them to a fine powder. The powder is now collected and placed between pieces of parchment, round which a wet cloth is to be folded ; it is thus left for about a week, being stirred each day, however, to ensure an equal damping of the powder by the moisture which permeates the parchment. To apply the powder, a certain quantity is placed on a slab and made into a paste with water ; the workman then takes up a small portion with his thumb, which he rubs upon the cleaned surface of the part to be gilt ; the crevices, fillets, or grooves are rubbed with pieces of cork cut to the shape required for the purpose, and the corners, or sharp angles, are rubbed with a stick of soft wood ; such as willow or poplar. When the articles have been gilt in this way, they are finished by burnishing in the usual manner. When a red-coloured gold is required, a small portion of copper is added to the other ingredients when preparing the salt of gold as above described. CHAPTER XIII. ELECTRO-DEPOSITION OF GOLD. Gilding by Direct Current, or Electro-Gilding. Preparation of Gilding Solu- tions. Gilding Solutions : Becquerel's. Fizeau's. Wood's. M. de Briant's. French Gilding Solutions. Gilding Solutions made by the Battery Process. De Ruolz's. Cold Electro-Gilding Solutions. Observations on Gilding in Cold Baths. Ferrocyanide Gilding Solu- tion. Watt's Gilding Solution. Record's Gilding Bath. Gilding by Direct Current, or Electro-gilding. In gilding by dipping, or simple immersion, it is obvious that, as a rule, only a limited amount of gold can be deposited upon the work, and that the application of this method of gilding, therefore, must be confined to cheap classes of work, or to articles which will not be subjected to much friction in use. In gilding by the separate current, on the other hand, we are enabled to deposit the precious metal not only of any required thickness, but also upon many articles which it would be practically impossible to gild properly by simple immersion in a solu- tion of gold. Electro -gilding is performed either with hot or cold solutions ; but for most practical purposes hot solutions are employed. When gold is deposited from cold solutions, the colour of the deposited metal is usually of a yellow colour, and not of the rich orange-yellow tint which is the natural characteristic of fine gold , the deposit, more- over, is more crystalline, and consequently more porous in cold than hot solutions, and is therefore not so good a protective coating to the underlying metal. The gold deposited from hot solutions is not only of a superior colour and of closer texture, but it is also obtained with much greater rapidity ; indeed, from the moment the articles are im- mersed in the gilding bath, all things being equal, the colour, thick- ness, and rapidity of the deposit are greatly under the control of the operator. In a few seconds of time an article may be gilded of the finest gold colour, with scarcely an appreciable quantity of the precious metal, while in the course of a very few minutes a coating of sufficient thickness may be obtained to resist a considerable amount of wear. The superior conductivity of hot gilding solutions enables the operator GILDING SOLUTIONS. 1 67 to gild many metallic surfaces, as tin, lead, Britannia metal, and steel, for example, which he could not accomplish satisfactorily with cold solutions ; moreover, hot gilding solutions readily dissolve any trace of greasy matter, or film of oxide which may be present on the sur- face of the work, through careless treatment, and thus clean the surface of the work for the reception of the gold deposit. Since cold gilding solutions are occasionally used in electro -de- position, these will be treated separately, as also the special purposes to which they are applied. Preparation of Gilding Solutions. In making up gilding baths from either of the following formulae, except in such cases as will be specified, the gold is first to be converted into chloride, as before directed ; but the actual weight of the pure metal required for each specified quantity of solution will be given in each case. Of all the solutions of gold ordinarily employed in the operations of electro -gilding by the direct current, the doulle cyanide of gold and potas- sium, when prepared from pure materials, is undoubtedly the best, and has been far more extensively employed than any other. It is very important, however, in making up gold solutions, to employ the purest cyanide that can be obtained. A very good article, commonly known as " gold cyanide," if obtained from an establishment of known respectability, is well suited to the purpose of preparing these solutions. The following formulae are those which have been most extensively adopted in practice ; but it may be well to state that some persons employ a larger proportion of gold per gallan of solution than that given, a modification which may be followed according to the taste of the operator ; but we may say that excellent results have been obtained by ourselves when employing solutions containing much less metal than some extensive firms have been known to adopt. Gilding Solutions. I. To make one quart of solution, convert i ^ dwt. of fine gold into chloride as before, then dissolve the mass in about half a 'pint of distilled water, and allow the solution to rest so that any trace of chloride of silver present may deposit. Pour the clear liquor, which is of a yellow colour, into a glass vessel of con- venient size, and then dissolve about half an ounce of cyanide in four ounces of cold water, and add this solution, gradually, to the chloride of gold, stirring with a glass rod. On the first addition of the cyanide, the yellow colour of the chloride solution will disappear, and on fresh additions of the cyanide being made, a brownish precipitate will be formed, when the cyanide solution must be added, gradually, until no further precipitation takes place. Since the precipitate is freely soluble in cyanide of potassium, great care must be exercised not to add more of this solution than is necessary to throw down the metal in the form of cyanide of gold. To determine the right point at which 1 68 ELECTRO-DEPOSITION OF GOLD. to stop, the precipitate should now and then be allowed to fall, so that the clear supernatant liquor may be tested with a drop of the cyanide solution, delivered from one end of the glass rod ; or a portion of the clear liquor may be poured into a test tube, or other glass vessel, and then tested with the cyanide. If cyanide has been accidentally added in excess, a little more chloride of gold must be added to neutralise it. The precipitate must be allowed to settle, when the supernatant liquor is to be poured off, and the precipitate washed several times with distilled water. Lastly, a little distilled water is to be added to the precipitate, and a sufficient quantity of cyanide solution poured in to dissolve it, after which a little excess of cyanide solution must be added, and the solution then made up to one quart with distilled water. Before adding the final quantity of water, however, it is a good plan, when convenient to do so, to pour the concentrated solu- tion into an evaporating dish, and to evaporate it to dryness, which may be most conveniently done by means of a sand-bath, after which the resulting mass is to be dissolved in one quart of hot distilled water, and, should the solution work slowly in gilding, a little more cyanide must be added. The solution should be filtered before using, and must be worked hot, that is at about 130 Fahr. II. Take the same quantity of gold, and form into chloride as before, and dissolve in half a pint of distilled water ; precipitate the gold with ammonia, being careful not to add this in excess. The pre- cipitate is to be washed as before, but must not be allowed to become dry, since it will explode with the slightest friction when it is in that state. A strong solution of cyanide is next added until the precipi- tate is dissolved. The concentrated solution is now to be filtered, and finally, distilled water added to make one quart. Of course it will be understood that the quantity of solution given in this and other formulae merely represents the basis upon which larger quantities may be prepared. This solution must not be evaporated to dryness. III. Becquerefs Solution. This is composed of ChlorTde of gold .... i part Ferrocyanide of potassium . *. 10 parts Water 100 The above salts are first to be dissolved in the water ; the liquid is then to be filtered ; 100 parts of a saturated solution of ferrocyanide of potassium are now to be added, and the mixture diluted with once or twice its volume of water. "In general, the tone of the gilding varies according as this solution is more or less diluted ; the colour is most beautiful when the liquid is most dilute, and most free from iron [from the ferrocyanide]. To make the surface appear bright, it is sufficient to wash the article in water acidulated with sulphuric acid, rubbing it gently with a piece of cloth." FRENCH GILDING SOLUTIONS. 169 IV. Fizeau's Solutions, (i.) I part of dry chloride of gold is dissolved in 160 parts of distilled water ; to this is added, gradually, solution of a carbonated alkali in distilled water, until the liquid becomes cloudy. This solution may be used immediately. (2.) i gramme of chloride of gold and 4 grammes of hyposulphite of soda are dissolved in i litre of distilled water. V. Wood's Solution. 4 ounces (troy) of cyanide of potassium and i ounce of cyanide of gold are dissolved in i gallon of dis- tilled water, and the solution is used at a temperature of about 90 Fahr., with a current of at least two cells. VI. M. de Briani's Solution. The preparation of this solution is thus described : ' ' Dissolve 34 grammes of gold in aqua regia, and evaporate the solution until it becomes neutral chloride of gold ; then dissolve the chloride in 4 kilogrammes of warm water, and add to it 200 grammes of magnesia ; the gold is precipitated. Filter, and wash with pure water ; digest the precipitate in 40 parts of water mixed with 3 parts of nitric acid, to remove magnesia, then wash the remaining [resulting] oxide of gold, with water, until the wash -water exhibits no acid reaction with test-paper [litmus-paper]. Next dissolve 400 grammes of f errocyanide of potassium [yellow prussiate of potash] and 100 grammes of caustic potash in 4 litres of water, add the oxide of gold, and boil the solution about twenty minutes. When the gold is dissolved, there remains a small amount of iron precipitated which may be removed by filtration, and the liquid, of a fine gold colour, is ready for use ; it may be employed either hot or cold." VII. French Gilding Sohitions. The following solutions are recom- mended by Roseleur as those which he constantly adopted in practice a sufficient recommendation of their usefulness. In the first of these both phosphate and bisulphite of soda are employed, with a small percentage of cyanide. The first formula is composed of Phosphate of soda (crystallised) . 60 parts Bisulphite of soda . . . . 10 Cyanide of potassium (pure) . . i part Gold (converted into chloride) . i Distilled or rain water . . . 1,000 parts. The second formula consists of Phosphate of soda .... 50 parts Bisulphite of soda . : . . 12$ Cyanide of potassium (pure) . . J part Gold i Distilled water . ; . . 1,000 parts. In making up either of the above baths, the phosphate of soda is first dissolved in 800 parts of hot water ; when thoroughly dissolved, the solution should be filtered, if not quite clear, and allowed to cool. I7O ELECTRO-DEPOSITION OF GOLD. The gold having been converted into solid chloride, is next to be dis- solved in 100 parts of water, and the bisulphite of soda and cyanide in the remaining 100 parts. The solution of gold is now to be poured slowly, with stirring, into the phosphate of soda solution, which acquires a greenish -yellow tint. The solution of bisulphite of soda and cyanide is next to be added, promptly, when the solution becomes colourless and is ready for use. If the solution of phosphate of soda is not allowed to become cold before the chloride of gold is added, a portion of this metal is apt to become reduced to the metallic state. Roseleur considers it of great importance to add the various solutions in the direct order specified. The first-named bath is recommended for the rapid gilding of articles made from silver, bronze, copper, and German silver, or other alloys of copper. The second bath is modified so as to be suitable for gild- ing steel, as also cast and wrought iron directly ; that is, without being previously coated with copper. The solutions are worked at a temper- ature of from 122 to 176 Fahr. In working the first bath, Roseleur says, " Small articles, such as brooches, bracelets, and jewellery-ware in general, are kept in the right hand with the conducting wire, and plunged, and constantly agitated in the bath. The left hand holds the anode of platinum wire, which is immersed more or less in the liquor according to the surface of the articles to be gilt. Large pieces are suspended by one or more brass rods, and, as with the platinum anode, are moved about. The shade of the gold deposit is modified by dipping the platinum anode more or less in the liquor, the paler tints being obtained when a small surface is exposed, and the darker shades with a larger surface. Gilders of small articles generally nearly exhaust their baths, and as soon as they cease to give satisfac- tory results, make a new one, and keep the old bath for coloured golds, or for beginning the gilding of articles, which are then scratch- brushed and finished in a fresh bath. Those who gild large pieces maintain the strength of their baths by successive additions of chloride of gold, or, what is better, of equal parts of ammoniuret of gold and cyanide of potassium." Articles of copper or its alloys, after being properly cleaned, are sometimes passed through a very weak solution of nitrate of mercury before being immersed in the gilding bath. The above system of working without a gold anode is certainly economical for cheap jewellery, or such fancy articles as merely require the colour of gold upon their surface ; but it will be readily understood that solutions worked with a platinum anode would be useless for depositing a durable coating of gold upon any metallic surface, unless the addition of chloride of gold were constantly made. GILDING SOLUTIONS MADE BY THE BATTERY PROCESS. 17 1 VIII. Gilding Solutions Made by the Battery Process. The system of forming gold solutions by electrolysis has much to recommend it ; the process is simple in itself ; it requires but little manipulation, and in inexperienced hands is less liable to involve waste of gold than the ordinary chemical methods of preparing gilding solutions. A gold bath made by the battery process, moreover, if the cyanide be of good quality, is the purest form of solution obtainable. To prepare the solution, dissolve about I pound of good cyanide in i gallon of hot distilled water. When all is dissolved, nearly fill a perfectly clean and new porous cell with the cyanide solution, and stand it upright in the vessel containing the bulk of the solution, taking care that the liquid stands at the same height in each vessel. Next attach a clean block of carbon or strip of clean sheet copper to the negative pole of a voltaic battery, and immerse this in the porous cell. A gold anode attached to the positive pole is next to be placed in the bath, and the voltaic action kept up until about I ounce of gold has been dissolved into the solution, which is easily determined by weighing the gold both before and after immersion. The solution should be maintained at a temperature of 130 to 150 Fahr. while it is under the action of the current. Another method of preparing gold solutions by the battery process, is to attach a large plate of gold to the positive, and a similar plate of gold or block of carbon to the negative electrode, both being im- mersed in the hot cyanide solution as above, and a current from 2 Daniell cells passed through the liquid. The negative electrode should be replaced by a clean cathode of sheet German silver for a few moments occasionally, to ascertain whether the solution is rich enough in metal to yield a deposit, and when the solution is in a con- dition to gild German silver promptly, with an anode surface of about the same extent, the bath may be considered ready for use. The proportion of gold, per gallon of solution, may be greatly varied, from ^ an ounce, or even less, to 2 ounces of gold per gallon of solution being employed, but larger quantities of cyanide must be used in proportion. While the gold is dissolving into the solution, the liquid should be occasionally stirred. The bath should be worked at from 130 to 150 Fahr., the lower temperature being preferable. In making solutions by the battery process, the position of the anode should be shifted from time to time, otherwise it is liable to be cut through at the part nearest the surface of the solution (the waterline] where the electro -chemical action is strongest. A good way to prevent this is to punch a hole at each corner of the gold anode, and also a hole midway between each of the corner holes, through which the supporting hook may be successively passed ; this arrangement will admit of eight shif tings of the anode. Another plan is to connect 172 ELECTRO-DEPOSITION OF GOLD. a stout platinum wire or a bundle of fine wires to the anode by means of gold solder, and to immerse the ivhole of the anode in the cyanide solution ; this is a very good plan for dissolving the gold uniformly, since the platinum is not acted upon by the cyanide. Sometimes gold wires are used to suspend the anode, in which case the wire should be protected from the action of the cyanide by slipping a glass tube or piece of vulcanised india-rubber tubing over it. IX. De Ruolz's Solution. 10 parts of cyanide are dissolved in 100 parts of distilled water, and the solution then filtered ; I part of cyanide of gold, carefully prepared and well washed, and dried out of the influence of light, is now added to the filtered solution of cyanide. It is recommended that the solution be kept in a closed vessel at a temperature of 60 to 77 Fahr. for two or three days, with frequent stirring, and away from the presence of light. X. Cold Electro-gilding Solutions. The cold gilding bath is some- times used for very large objects, as clocks, chandeliers, &c., to avoid the necessity of heating great volumes of liquid. As in the case of hot solutions, the proportions of gold and cyanide may be modified considerably. Any double cyanide of gold solution may be used cold, provided it be rich both in metal and its solvent cyanide of potassium, and a sufficient surface of anode immersed in the bath during electro- deposition. For most practical purposes of cold gilding, the following formulae are recommended by Roseleur : Fine gold 10 parts Cyanide of potassium of 70 per cent. . . 30 Liquid ammonia 50 Distilled water 1,000 The gold is converted into chloride and crystallised, and is then dis- solved in a small quantity of water ; the liquid ammonia is now to be added, and the mixture stirred. The precipitate, of a yellowish brown colour, is aurate of ammonia, ammoniuret of gold, or fulminating gold, and is a highly explosive substance, which must not on any account be allowed to become dry, since in that state it would detonate with the slighest friction, or an accidental blow from the glass stirrer. Allow the precipitate to subside, then pour off the supernatant liquor and wash the precipitate several times ; since the washing waters will retain a little gold, these should be set aside in order that the metal may be recovered at a future time. The same rule should apply to all washing waters, either from gold or silver precipitates. The aurate of gold is next to be poured on a filter of bibulous paper, that is filtering paper specially sold for such purposes. The cyanide should, in the interim, have been dissolved in the remainder of the water. The cyanide solution is now to be added to the precipitate, COLD ELECTRO-GILDING SOLUTIONS. 1^3 which it readily dissolves, and this may be conveniently done, if a large filter is used, by pouring it on to the wet precipitate while in the filter, a portion at a time, until the aurate of ammonia has disap- peared, and the whole of the cyanide solution has passed through the filter. This will be a safer plan than removing the precipitate from the filter ; or the filter may be suspended in the cyanide solution until the aurate is all dissolved. The solution is finally to be boiled for about an hour, to drive off excess of ammonia. After this solution has been worked for some time it is apt to become weaker in metal, in which case it must be strengthened by additions of aurate of ammonia. For this purpose, a concentrated solution of the gold salt in cyanide of potassium is kept always at hand, and small quantities added to the bath from time to time when necessary. It is preferable to employ good ordinary cyanide in making up the bath, and pure cyanide for the concentrated solution. 2. This solution is composed of Fine gold . . . . . parts Pure cyanide of potassium . . 20 Or commercial cyanide . . . 30 to 40 parts Distilled water .... 1,000 parts. The gold is to be formed into chloride and crystallised, as before, and dissolved in about 200 parts of the water ; the cyanide is next to be dissolved in the remainder of the water, and, if necessary, filtered. The solutions are now to be mixed and boiled for a short time. When the solution becomes weakened by use, its strength is to be aug- mented by adding a strong solution of cyanide of gold, prepared by adding a solution made from I part of solid chloride dissolved in a little water, and from i to i| parts of pure cyanide of potassium, also dissolved in distilled water, the two solutions being then mixed together. 3. This solution consists of Ferrocyanide of potassium (yellow prussiate of potash) 20 parts Pure carbonate of potash ...... 30 Sal-ammoniac 3 Gold . . . ,.<-.. . . . 15 Water 1,000 All the salts, excepting the chloride of gold, are to be added to the water, and the mixture boiled, and afterwards filtered. The chloride of gold is next to be dissolved in a little distilled water and added to the filtered liquor. Some persons prefer employing the aurate of ammonia in place of the chloride of gold, and sometimes small 174 ELECTRO-DEPOSITION OF GOLD. quantities of prussic acid are added to the bath, to improve the bright- ness of the deposit ; but this acid makes the bath act more slowly. The deposit of gold from cold solutions varies greatly as to colour. When the bath is in its best working condition, and a brisk current of electricity employed, the gold should be of a pure yellow colour ; sometimes, however, it is several shades lighter, being of a pale yellow ; it sometimes happens that the gold will be deposited of an earthy grey colour, in which case the articles require to be cautiously scratch -brushed, and afterwards coloured by the or-moulu process to be described hereafter. The proportion of cyanide in these baths should be about twice that of the chloride of gold ; but since the cyanide is of variable quality, it may often be necessary to employ an excess, which is determined by the colour of the deposit ; if the gold is in excess the deposit may be of a blackish or dark red colour ; or if, on the contrary, cyanide preponderates, the operation is slow and the gold of a dull grey colour, and not unfrequently, when the bath is in this condition, the gold becomes re-dissolved from the work in solution, either entirely or in patches. When the bath is not in good working order, the gold anode must be withdrawn from the solution, otherwise it will become dissolved by the cyanide. It is a ''remarkable phenomenon," says Roseleur, " that solutions of cyanides, even without the action of the electric current, rapidly dissolve in the cold, or at a moderate temperature, all the metals, except platinum, and that at the boiling point they have scarcely any action upon the metals." Observations on Gilding in Cold Baths. When a pure yellow colour is desired, a newly-prepared double cyanide of gold solution, in which a moderate excess only of cyanide is present, and containing from i to 2 ounces of gold per gallon, will yield excellent results with the current from a single Wollaston or Daniell battery ; but suffi- cient anode must be exposed in the solution to admit of the deposit taking place almost immediately after the article is immersed in the bath. The anode may then be partially raised out of the solution, and the deposition allowed to take place without further interference than an occasional shifting of the object to coat the spot where the slinging wire touches. After the article has been in the bath a minute or so, the operator may assure himself that deposition is pro- gressing satisfactorily by dipping a piece of clean silvered copper wire in the bath and allowing it to touch the object being gilt, when, if the end of the wire becomes coated with gold, he may rest assured that deposition is proceeding favourably. Care must be taken, how- ever, that the deposit is not taking place too rapidily, for it is abso- lutely necessary that the action should Jbe gradual, otherwise the gold may strip off under the operation of the scratch-brush. If any OBSERVATIONS ON GILDING IN COLD BATHS. 175 portions of the -work appear patchy or spotted, the pieces must be removed from the bath, rinsed, and well scratch-brushed. As in hot gilding, the plater will find the scratch-brush his best friend when the work presents an irregular appearance. It is not advisable to employ a current of high intensity in cold gilding ; the Wollaston or Daniell batteries, therefore, are most suitable, and when a series of cells are required to gild large surfaces or a considerable number of objects, the poles of the batteries should be connected for quantity, that is all the positive electrodes should be connected to the anodes, and all the negative electrodes put in com- munication with the conducting-rod supporting the work in the bath. After deposition has taken place to some extent, an extra cell may be connected, followed by another, if necessary, and so on ; but while only a thin coating of gold is upon the work, the strength of the current should be kept low ; deposition takes place more slowly upon gold than upon copper or its alloys, therefore an increase of battery power becomes a necessity after a certain thickness of gold has been de- posited. If the current be too weak, on the other hand, the deposit is apt to occur only at the prominent points of the article, and upon those portions which are nearest the anode. It sometimes happens, with newly made baths, that when the articles are shifted to expose fresh surfaces to the anode, the gold already deposited upon the work becomes dissolved off ; when such is the case, it generally indicates that there is too great an excess of cyanide in the solution, although the same result may occur if there be too little gold or the current too feeble. When the gold deposited in a cold bath is of an inferior colour, the article may be dipped in a weak solution of nitrate of mercury until it is entirely white ; it is then to be heated to expel the mercury, and afterwards scratch-brushed. Or the article may be brushed over with the "green colour," described in another chapter, and treated in the same way as bad-coloured gilding from hot solutions. XI. Ferrocyanide Gilding Solution. To avoid the use of large quan- tities of cyanide of potassium in gilding solutions, the following process has been proposed : In a vessel, capable of holding 4 litres, are dissolved in distilled water 300 grammes of ferrocyanide of potassium, and 50 grammes of sal-ammoniac ; 100 grammes of gold, dissolved in aqua regia and evaporated to expel the acid as usual, are dissolved in I litre of distilled water. Of this solution, 200 cubic centimetres are added, little by little, to the ferrocyanide solu- tion, when oxide of iron (from the ferrocyanide) is precipitated. The liquid is allowed to cool, and is then filtered and made up to 5 litres, when the bath is ready for use. Since it is not a good con- ductor, however, and deposits oxide of iron upon the anode, a small 176 ELECTRO-DEPOSITION OF GOLD. quantity of cyanide is added, but not sufficient to evolve hydrocyanic acid on boiling. The bath should be worked at from 100 to 150 Fahr. When the bath ceases to yield a good deposit, 200 c.c. of the gold solution must be added gradually, as before ; if it is desired to increase this proportion of gold, one -tenth of the quantity of the other salts must also be added to the bath. XII. Watt's Gilding Solution. A gilding solution which the author has used very extensively, and which he first adopted about the year 1838, is formed as follows : i^ pennyweight of fine gold is converted into chloride, as before described, and afterwards dissolved in about | pint of distilled water. Sulphide of ammonium is now added gradually with stirring, until all the gold is thrown down in the form of a brown precipitate. After repose the supernatant liquor is poured off, and the precipitate washed several times with distilled water ; it is then dissolved in a strong solution of cyanide of potassium, a moderate excess being added as free cyanide, and the solution thus formed is diluted with distilled water to make up one quart. Before using this solution for gilding it should be maintained at the boiling point for about half an hour, and the loss by evaporation made up by addition of distilled water. This bath yields a fine gold colour, and if strengthened from time to time by a moderate addition of cyanide, will continue to work well for a very considerable period ; it should be worked at about 130 Fahr. The above solution gives very good results with a Daniell battery, and the articles to be gilt do not require quicking, as the deposit is very adherent. XIII. Record's Gilding Bath. This solution, for which a patent was obtained in 1884, is formed by combining nickel and gold solutions, by which, the patentee avers, a considerable saving of gold is effected. To make this solution, he dissolves 5 ounces of nickel salts in about 2 gallons of water, to which 12 ounces of cyanide of potassium is added, " so that the nickel salts may be taken up quite clear." The solution is then boiled until the ammonia contained in the nickel salts is entirely evaporated. This solution is then added to the ordinary gold solution containing I ounce of gold. The proportions given are preferred, but may be varied at will. CHAPTER XIV. ELECTED -DEPOSITION OF GOLD (continued). General Manipulations of Electro-gilding. Preparation of the Work. Dead Gilding. Causes which affect the Colour of the Deposit. Gilding Gold Articles. Gilding Insides of Vessels. Gilding Silver Filigree Work. Gilding Army Accoutrement Work. Gilding German Silver. Gilding Steel. Gilding Watch Movements. General Manipulations of Electro-Gilding. In small gilding operations, the apparatus and arrangements are of an exceedingly simple character, and need not involve more than a trifling outlay. A 12-inch Daniell cell, or a small battery (say a half -gallon cell), con- structed as follows, will answer well for gilding such small work as Albert chains, watch cases, pins, rings, and other work of small dimensions. This battery consists of a stone jar, within which is placed a cylinder of thin sheet- copper, having a binding screw attached. Within this cylinder is placed a porous cell, furnished with a plate or bar of amalgamated zinc, to the upper end of which a binding screw is connected. A dilute l ^' ^' solution of sulphuric acid is poured into the porous cell, and a nearly saturated solution of sulphate of copper, moderately acidified with sulphuric acid, is poured into the outer cell. This simple battery costs very little, is very constant in action, and may readily be constructed by the amateur or small operator. The gilding bath may consist of one quart of solution, prepared from any of the for- mulae given; a square piece of rolled gold, about 2 by 2 inches, weighing about five pennyweights, or even less, will serve for the anode ; and an enamelled iron saucepan may be used to contain the solution. Since gilding baths require to be used hot (about 130' Fahr.), except for special purposes, the solution may be heated by means of a small 4-burner oil lamp, such as is shown in Fig. 74, the gilding vessel being supported upon an iron tripod or ordinary meat stand. With this simple arrangement, it is quite possible to gild such articles as we have named, besides smaller articles, such as brooches, lockets, and scarf-pins ; and provided the gold anode be replaced, as w 178 ELECTRO-DEPOSITION OP GOLD. it becomes "worn away" in use, and the solution kept up to its normal height by additions of distilled water to make up for loss by evaporation, the same bath will be capable of gilding a good amount of small work. The bath will, however, require small additions of cyanide every now and then, that is when it shows signs of working slowly, or yields a deposit of an indifferent colour ; the battery, also, will need proper attention by renewal of the dilute acid occasionally. In working on the small scale referred to, in the absence of a proper scratch- brush lathe, the hand " scratch -brush," Fig. 76, may be resorted to : this consists simply of a single scratch-brush, cut open at one end, and spread out before using, by well brushing it against some hard metal substance ; to mollify the extreme harshness of the newly cut brass wire, of which the brush is composed, it may advantageously be rubbed to and fro upon a hard flagstone, after which it should be rinsed before using. To apply the hand scratch -brush, prepare a little warm soap and water, into which the brush must be dipped frequently while being used. In brushing Albert chains or similar work, the swivel may be hooked on to a brass pin, driven into the corner of a bench or table, while the other end of the chain is held in the hand ; while thus stretched out, the moistened brush is dipped in the suds, and lightly passed to and fro from end to end, and the position of the article must be reversed to do the opposite side ; to brush those parts of the links which cannot be reached while the chain is outstretched, the chain is held in the hand, and one part at a time passed over the first finger, by which means the unbrightened parts of the links may be readily scratch-brushed. It is important, in scratch -brushing, to keep the brush constantly and freely wetted as above. Gilding on a somewhat larger scale say with one or two gallons of gold solution may be pursued without any very great outlay, and yet enable the gilder to do a considerable amount of work of various kinds and dimensions in the course of an ordinary working day. The arrangement we would suggest may be thus briefly explained : for the battery, a one-gallon Bunsen, or Smee, or an 1 8 -inch Daniell cell ; for the anode, two or more ounces of fine gold rolled to about 6 by 3 inches, to which a stout piece of platinum wire, about 4 inches in length, should be attached by means of gold solder. A small binding screw may be employed to connect the platinum wire with the positive electrode of the battery. The object of using platinum wire is to enable the whole of the anode to be immersed in the solution when a large surface is necessary, and which could not be properly done if copper wire were used, since this metal (unlike platinum, which is not affected by the solution) would become dissolved by the bath, and affect the colour of the deposit. A simple method of heat- ing the gilding solution and keeping it hot while in use will be seen ELECTEO-GILDING. 1 79 in the accompanying engraving, Fig. 75. The gilding bath rests upon a short-legged iron tripod, beneath which is a perforated gas burner, supplied with gas by means of flexible india-rubber tubing connected to an ordinary gas-burner. Perforated burners are readily pro- curable, and are of trifling cost. For brightening small articles the hand scratch-brush referred to (Fig. 76) may be used, but, for the convenience pj 7 - of handling, it should be tied to a stick, to prevent it from bending in the hand. The brush is to be dipped in soap-suds or stale beer frequently while being ap- plied to the work. In gilding upon the above moderate scale, however, the lathe scratch-brush, described further on, will be as necessary as in still larger operations : an ordinary foot lathe, such as is used in silver plating (which see), is the machine generally used for this purpose, and is of very simple construction. Such lathes, or their chief parts, may often be procured second hand for a very moderate sum. As in scratch-brushing electro -silvered or plated work, stale beer is employed to keep the brushes constantly wet while the lathe is being used, and the work is pressed very lightly against the revolving brushes. It is important, however, when the scratch-brushes are new, that they should have some hard metallic surface pressed against them while in brisk motion for a few minutes, to spread them well out or make them brushy, and to reduce the extreme harshness of the newly-cut brass wire ; if this -p. g precaution be not followed, the gold, if the coating be thin, may become partially removed from the gilt article, rendering its surface irregular and of an indifferent colour, necessitating regild- ing and scratch -brushing. Preparation of the Work. In electro -gilding watch chains of various kinds, brooches, lockets, scarf-pins, and other small articles of jewellery, it is generally sufficient to well scratch-brush and rinse them, after which they are at once put into the bath. A preparatory dip in a hot potash bath, however, may be resorted to. After scratch- brushing, a short length of copper "slinging" wire is attached to the article, and the free end is connected to the negative electrode of the battery by simply coiling it around the stouter wire several times ; the ends of both wires, however, should previously be cleaned by l8o ELECTRO-DEPOSITION OF GOLD. means of a piece of emery cloth. When the articles are first dipped into the solution, they should be gently moved about, so that the deposit may be regular. Chains should be shifted from their position occasionally, so that those portions which are in contact with each other may become gilt ; this may generally be done by giving the chain a brisk shake from time to time, and also by slipping the chain through the loop of the slinging wire. If brooches and other similar articles are slung by a loose loop of wire, gentle shaking is all that is necessary to shift their position on the slinging wire. Some operators, when gilding metal chains or other work manufac- tured from copper or its alloys brass, gilding metal, and German silver prefer to quick them after steeping in the potash bath and scratch -brushing. In this case it will be necessary to have a quicking bath or "mercury dip " always at hand. The mercury dip consists of a very dilute solution of nitrate or cyanide of mercury, and after the articles have been whitened in this bath, they must be well rinsed in clean water before being immersed in the gilding bath. The object of mercury dipping is to ensure a perfect adhesion of the gold deposit. The author has never, either in electro -gilding or silvering, found it necessary to apply the quicking process, but the solutions both of gold and silver were not prepared in the same way as those ordinarily adopted by the trade. The solutions which the author worked for a great number years without the aid of the mercurial coating are men- tioned in the chapters describing the preparation of gilding and silvering baths. Dead Gilding. There are several methods of preparing the work so that the deposit instead of being more or less bright when removed from the gilding-bath, may present a dead or frosted appearance, which is not only exceedingly beautiful in the rich dulness of its lustre, but is absolutely necessary for certain classes of work, portions of which are relieved by burnishing. To obtain a deposit of a somewhat dead lustre, copper and brass articles are dipped for a moment in a mixture of equal parts of oil of vitrol and nitric acid, to which is added a small quantity of common salt. The articles are slung on a stout wire, coiled into a loop, and dipped in the nitro- sulphuric acid " dip " for an instant, and immediately rinsed in clean water, kept in a vessel close to the dipping acid ; if not sufficiently acted upon during the first dip, they must be again steeped for a moment, then rinsed in several successive waters, and at once put into the gilding bath. There should be as little delay a possible in transferring the articles to the gold bath, after dipping and rinsing, since copper and its alloys, after being cleaned by the acid and rinsed, are very susceptible of oxidation, even a very few moments being sufficient to tarnish them. If the mercury dip is employed, the work must be dipped in the CAUSES WHICH AFFECT THE COLOUR OF THE DEPOSIT. l8l quicking bath immediately after they have been rinsed from the acid dip. The surface of articles may be rendered still more dead, or frosted, by slightly brushing them over with finely powdered pumice, or, still better, ordinary bath brick reduced to a powder. By this means the extreme point of dulness, or deadness, may be reached with very little trouble. "Work which requires to be burnished after gilding should first be steeped in the potash bath, and after rinsing be well scratch - brushed, or scoured with silver sand, soap, and water, when, after again rinsing in hot water, it is ready for the bath. In scouring the work with sand and soap, it is necessary to use warm water freely ; the soap may be conveniently applied by fixing a large piece of this material say Ib. of yellow soap to the scouring-board by means of four upright wooden pegs or skewers, forming a square about z\ inches each way, within which the soap may be secured firmly, and will retain its position until nearly used up. By this simple plan the soap, being a fixture, may be rubbed with the scouring-brush, as occasion may require, without occupying a second hand for the purpose. Causes which Affect the Colour of the Deposit. In the opera- tion of gilding, the colour of the deposit may be influenced almost momentarily in several ways. Assuming that the current of elec- tricity is neither too strong nor too weak, and the bath in perfect order, if too small a surface of anode is immersed in the bath, the gold deposit will be of a pale yellow colour. Or, on the other hand, if too large a surface of anode is exposed in solution, the deposit may be of a dark brown or "foxy" colour, whereas the mean be- tween these two extremes will cause the deposit to assume the rich orange-yellow colour of fine or pure gold. Again, the colour of the deposit is greatly affected by the motion of articles while in the bath ; for example, if the gilding be of a dark colour, by briskly moving the articles about in the bath, they will quickly assume the proper colour. The temperature of the solution also affects the colour of the deposit, the tone being deeper as the solution becomes hotter, and vice versa. The colour of the gilding is likewise much affected by the nature of the current employed. A weak current from a Wollaston or Daniell battery may cause the deposit to be of a paler colour than is desired, whereas a Smee, Grove, or Bunsen (but more especially the latter) will produce a deposit of a far richer tone. The presence of other metals in the solution, but copper and silver more particularly, will alter the colour of the deposit, and therefore it is of the greatest importance to keep these metals out of the ordinary gilding solution by careful means. When gilding in various colours is needed, recourse must be had to the solutions described elsewhere, 1 82 ELECTEO-DEPOSITION OF GOLD. but on no account should the gilding bath used for ordinary work be allowed to become impregnated with even small quantities of any other metal. When we state that trifling causes will sometimes inter- fere with the natural beauty of the pure gold deposit, the importance of preserving the baths from the introduction of foreign matters will be at once apparent. Another thing that affects the colour of the gilding is the accumulation of organic matter, that is, vegetable or animal matter, which is introduced into the bath by the articles im- mersed in it ; thus, greasy matter from polished work, and beer from the scratch-brush, will sometimes lodge in the interstices of hollow work, and escape into the bath even after the articles have been rinsed ; each in their turn convey organic matter to the gold solution, by which it acquires a darkened colour ; indeed, we have known solu- tions acquire quite a brown colour from these causes. In our expe- rience, however, the presence of a small amount of such foreign matter, in moderation, has often proved of advantage, especially in the gilding of insides of vessels, when a rich and deep -toned gilding is required : a solution in this condition we should prefer, for insides of cream ewers, sugar-bowls, and goblets, to a newly -prepared gold solution ; indeed, when a bath works a little foxy, it is, to our mind, in the best condition for these purposes, since the former is apt to yield a deposit which is too yellow for such surfaces. There is an extreme, however, which must be avoided, that is when the bath yields a brown- yellow deposit, which is very unsightly, though not uncommonly to be seen in our shop windows. When the gilding upon chains or articles of that class is of a deep brownish -yellow colour when removed from the bath, it will, when scratch-brushed, exhibit a fine gold appearance, specially suited to this class of work, and more like jewellers' " wet colour work " than electro -gilding, which will render it more acceptable to those who are judges of gold colour. Indeed, when the electro -gilding process was first introduced, it was a general complaint amongst shopkeepers that electro -gilding was too yellow, and that electro -gilt work could easily be distinguished from coloured gold in consequence, which was admitted to be a serious defect, since a person wearing a gilt article would naturally wish it to be assumed by others to be of gold. In gilding such articles, therefore, the aim of the gilder should be to imitate as closely as possible the colour of gold jewellery, whether it be dry or wet coloured work. In the latter there is a peculiar depth and softness of tone which is exceedingly pleasing; in dry coloured work a rich dead surface is produced which it is not so difficult to imitate in electro-gilding. The processes of " colouring " articles of gold will be given in another chapter, since a knowledge of these processes is not only useful but often necessary to an electro-gilder, GILDING INSIDE S OF VESSELS. 183 in whose hands such work may sometimes be placed for restoration or recolouring. Gilding Gold Articles. Although "painting the lily " would not be a very profitable or successful operation, articles made from inferior gold alloys are frequently sent to the electro -gilder to be " coloured," that is, to receive a slight film of pure gold, to make them look like gold of a superior quality, like coloured gold, in fact. Although such an imposition is a positive fraud upon the purchaser, the electro -gilder has little choice in the matter ; if his natural scruples would tempt him to refuse such unfair work, as it may be called, he knows full well that others will readily do the work and "ask no questions ; " he must therefore undertake it or lose a customer perhaps an important one. Albert chains, rings, pins, brooches, and a host of other articles manufactured from gold alloys of very low standard, are frequently " coloured " by electro-deposition, simply because the process of colouring by means of the " colouring salts " would rot them, if not dissolve them entirely. Gilding Insides of Vessels. Silver or electro -plated cream ewers, sugar-basins, mugs, &c., are electro-gilt inside in the following way: The inside of the vessel is first well scratch-brushed, for which pur- pose a special scratch -brush, called an end-brush, is used. Or this surface may be scoured with soap and water with a piece of stout flannel ; the vessel, after well rinsing, is then placed upon a level table or bench ; a gold anode, turned up in the form of a hollow cylinder, is now to be connected to the positive electrode of a battery, and lowered into the vessel, and supported in this position, care being taken that it does not touch the vessel at any point. The negative electrode is to be placed in contact with the vessel (Fig. 77), and hot gold solu- tion then carefully poured in, up to its extreme inner edge, below the mount, if it have one. A few moments after pouring in the gold solution, the anode should be gently moved to and fro, without coming in contact with the vessel itself, so as to render the deposit more uniform ; it may then be allowed to remain without interruption for a minute or so, when the gentle movement of the anode may be renewed for a few moments, these alternations of motion and repose being kept up for about five or six minutes or perhaps a little longer by which time a sufficiently stout coating is generally obtained. Moving the anode occasionally has the effect of rendering the deposit more regular, while it also exposes fresh surfaces of the solu- tion to the metal surfaces under treatment ; great care, how- 184 ELECTRO-DEPOSITION OP GOLD. ever, is necessary to avoid driving the solution over the orna- mental mount on the rim of the vessel. The lips of cream ewers, which the gold solution cannot reach when the vessel is filled with solution, are gilt by conducting the solution to such parts in this way : A small gold anode, with a short piece of copper wire attached, is enclosed in a piece of rag or chamois leather ; the end of this wire is then connected to the positive electrode (the article itself being in direct contact with the negative), and the pad, or " doctor," as it is sometimes called, is dipped in the gold solution and applied to the part to be gilt ; in this way, by repeatedly dipping the pad in the solution and conducting it over the surface, this part in a short time becomes sufficiently gilt ; since the lip of a cream ewer, however, is the most important part of the gilt surface, the application of the pad should be continued until a proper coating is obtained, and care must be taken that the point of junction between the two deposits of gold is not visible when the gilding is complete. We should prefer to gild the lip of such vessels first, and after well scratch -brushing, or scour- ing the interior, and especially the line where the two gildings will meet, then to gild the interior of the body of the vessel, and finally to scratch-brush the whole surface. In gilding the insides of vessels, it is important that the outsides and mounts, or mouldings, should be perfectly dry, otherwise the gold solution may, by capillary attraction, pass beyond its proper boundary and gold become deposited where it is not required, thus entailing the trouble and annoyance of re- moving it. Gilding Silver Filigree Work. A dead surface of silver is very apt to receive the gold deposit ununiformly, and this is specially so in the case of silver filigree work, the interstices of which cannot fully be reached by the scratch - brush ; the surfaces brightened by the scratch -brush readily receive the deposit, while those portions of the article which escape the action of the wire brush will sometimes fail to " take " the gold. When this is found to be the case, a large surface of anode should be immersed in the bath, and the article briskly moved about until the whole surface is coated, when the anode may be par- tially withdrawn, and a sufficient surface only exposed in the bath to complete the article as usual. In gilding work of this description it is necessary that a fair amount of free cyanide should be in the bath, but the excess must not be too great, or the deposit will be/or*/ a colour which must be strenuously avoided, since the brown tint will be visible more or less upon those interstices (especially the soldered parts) which the scratch-brush cannot reach. As a rule, filigree work should not be risked in an old gold solution in which organic matter or other impurities may be present. It is a good plan, after giving the article a quick coating in the way indicated, to rinse and " scratch " it GILDING ARMY ACCOUTREMENT WORK. 185 again, and then to re-immerse it in the bath. A solution for gilding filigree work should also be tolerably rich in gold about 5 penny- weights to the quart of solution being a good proportion, though some gilders use a still larger proportion of metal. In gilding filigree work a rather intense current is necessary ; a Bunsen battery, therefore, should be employed, or two Daniell cells arranged for intensity. Gilding Army Accoutrement Work. In the early days of electro- gilding, great difficulty was experienced by electro -gilders in imparting to sword-mounts, the threaded ornamentation of scabbards, and other army accoutrements the rich dead lustre, as the French term it, which the mercury gilders produced with so much perfection, and for a long period electro-gilders, in their anxiety to obtain contracts for gilding this class of work, made many unsuccessful attempts and suffered much disappointment from the repeated rejection of their work by the government authorities. At the period referred to, there was a great desire, if possible, to render the pernicious art of mercury gilding unnecessary, since it was too well known that those engaged in the art suffered severely from the effects of mercurial poisoning, by which their existence was rendered a misery to them, and their lives abbreviated to a remarkable degree. It may be stated, however, that the operations of gilding with an amalgam of gold and mercury were frequently conducted with little or no regard to the dangerous nature of the fluid metal which the workpeople were constantly handling, and the volatilised fumes of which they were as constantly inhaling. It was a happy epoch in the gilding art when deposition of gold by elec- tricity rendered so baneful a process, incautiously practised, compara- tively unnecessary. We say comparatively, because amalgam or mercury gilding is still adopted, though with a little better regard to the health of the workmen, for certain classes of work, for which, even up to the present period, electro -gilding is not recognised as a perfect substitute. To gild army accoutrement work, so as to resemble, as closely as possible, mercury gilding, the colour and general appearance of the matted or dead parts must be imitated very closely indeed. There are no articles of gilt work that look more beautiful by contrast than those in which dead surfaces are relieved by the raised parts and surrounding edges being brightened by burnishing, and this effect is charmingly illustrated in the mountings of the regulation sword of the British officer. Indeed this class of work, when properly finished, may be considered the perfection of beauty in gilding. To give the necessary matted surface to the chased portions of sword mounts, and work of a similar description, these parts should be brushed over with finely-powdered pumice, or bath-brick reduced to a powder and sifted, which latter substance answers the purpose very l86 ELECTRO-DEPOSITION OF GOLD. well. The application of either of these materials should be confined, as far as is practicable, to the chased parts of the article, so as to avoid rendering the surfaces to be afterwards burnished rough by the action of the pumice powder. The plain surfaces of the article may then be scoured with silver-sand, soap and water, or scratch- brushed ; but great care must be taken not to allow the scratch -brush to touch the surfaces that are to be left dead. Sometimes it is the practice to add a little aurate of ammonia to the gilding solution to produce a dead lustre in gilt work. When it is preferred to adopt the quicMng process, in gilding this class of work, the articles, after being quicked in the usual way, are placed in the bath until they have nearly received a sufficient deposit, when they are removed, rinsed, and the chased parts quickly brushed with pumice, as before, afte* which they are returned to the bath for a short time, or until the proper colour and matted appearance are imparted to the work. Gilding German Silver. This alloy qf copper, as also brass, will receive a deposit of gold in strong and warm cyanide solutions of gold without the aid of the battery; this being the case, in order to prevent the deposit from taking place too rapidly, when electro - gilding articles made from these alloys, the temperature of the solution should be kept rather low that is not beyond 120 Fahr. and only sufficient surface of anode immersed in the solution to enable the article to become gilt with moderate speed when /rs placed in the bath. It is also advisable that the gold solution should be weaker, both in gold and cyanide, than solutions which are used for gilding silver or copper work. If, however, quicking be adopted, these pre- cautions are not so necessary, since the film of mercury checks the rapidity of the gilding. Either method may be adopted according to the fancy of the gilder ; but for our own part, we would not suffer a particle of mercury to enter the gilding-room (except upon the amal- gamated plates of a battery) under any circumstances. Gilding Steel. The rapidity with which this metal receives a deposit of gold, even with a very weak battery current, in ordinary cyanide solutions, renders it imperative that a separate solution should be prepared and kept specially for steel articles. We have obtained excellent results by employing a bath composed of Ordinary double cyanide of gold solution . . i part. Water 4 to 6 parts. To this weakened solution a small quantity of cyanide of potassium may be added, and the current employed should be of low tension a Wollaston or Daniell battery being preferable. The temperature of the bath should be warm, but not hot. The surface of anode in solution must be just so much as will enable the gold to deposit soon GILDING STEEL. 1 87 after the article is placed in the bath, but not immediately after its immersion. In other words, if the gold is allowed to jump on, it will most assuredly as quickly jump off when the scratch-brush is applied. In preparing steel articles for gilding, the author has found that by scratch -brushing the work with vinegar, or very dilute hydrochloric acid, instead of sour beer, a very fine coating of copper (derived from the brass wire of the brushes) has been imparted to the articles, to which the gold deposit, from a weak bath, adhered with great firmness. A very successful method of gilding steel is to first copper or brass the articles in the alkaline solutions of these metals, as recommended for silvering steel and iron. The brass or copper solutions should be used warm, and be in good working order, so as to yield bright deposits of good colour. Before electro -brassing the articles, however, they must be thoroughly cleansed by scouring with silver-sand, soap and water, or scratch-brushed. Bright steel articles which are not required to have a durable coating of gold, but merely a slight film or "colouring" of the precious metal, generally need no preparation whatever, but may receive a momentary dip in the gilding bath, then rinsed in hot water, and at once placed in hot boxwood sawdust. In doing this cheap class of work, however, it is better to use a copper or platinum anode in place of the gold anode, and to make small additions of chloride of gold when the solution shows signs of becoming exhausted. It must be remembered, however, that the very dilute gold solution we have recommended for gilding steel con- tains in reality but very little gold, therefore, as it becomes further exhausted by working without a gold anode, additions of the chloride, in very small quantities, will require to be made so soon as the bath exhibits inactivity. For gilding polished steel, a nearly neutral solution of chloride of gold is mixed with sulphuric ether, and well shaken ; the ether will take up the gold, and the ethereal solution float above the denser acid. If the ethereal solution be applied by means of a camel-hair brush to brightly -polished steel or iron, the ether evaporates, and gold, which adheres more or less firmly, becomes reduced to the metallic state on the steel, and may be either polished or burnished. In gilding upon an extensive scale, where large objects, such as time-pieces, chalices, patens, and other work of large dimensions, have to be gilt, the depositing tanks are generally enamelled iron jacketed pans, heated by steam. These vessels are placed in rows near the wall of the gilding-room, in a good light, and suitable iron piping conveys the steam to the various tanks, each of which is provided with a suitable stopcock to admit or shut off the steam as required ; an exit pipe at the bottom of each " jacket " allows the water from the con- l88 ELECTRO-DEPOSITION OF GOLD. densed steam to escape into a drain beneath. Each of these tanks is provided with the usual conducting rods, and the current, which is sometimes derived from a magneto or dynamo machine in large estab- lishments, is conveyed by suitable leading wires or rods, attached to the wall at a short distance from the series of depositing vessels. In gilding large quantities of small articles, as steel pens, for example, a considerable number of gilding tanks, of an oblong form, are placed in a row, at a moderate distance apart, and the pens or other small objects are introduced into these as the gilders receive the work pre- pared for them. Gilding Watch Movements Continental Method. The re- markable beauty of the Swiss watch movements has always been the subject of much admiration, and for a long period this pleasing indus- try was solely confined to Switzerland ; France, however, eventually got possession of the method, and the art has been extensively practised in that country, but more especially at Besanqon and Morez, in Jura, and in Paris. M. Pinaire, a gilder at Besan^on, generously communicated the process to the late M. Roseleur, to whom we are indebted for the process. Pinaire's Method of Gilding Watch Movements. In gilding watch parts, and other small articles for watchmakers, gold is seldom applied directly upon the copper. In the majority of cases there is a pre- liminary operation, called graining, by which a vary agreeable grained and slightly dead appearance is given to the articles. If we examine carefully the inside of a watch we may see the peculiar pointed dead lustre of the parts. This peculiar bright dead lustre, if it may be so expressed, is totally different from that ordinarily obtained. For instance, it does not resemble the dead lustre obtained by slow and quick electro - deposition of gold, silver, or copper, which is coarser and duller than that of watch parts. Neither does it resemble the dead lustre obtained with the compound acids, which is the result of a multitude of small holes formed by the juxtaposition, upon a previ- ously even surface, of a quantity of more or less large grains, always in relief. The graining may be produced by different methods, and upon gold, platinum, and silver ; and since the latter metal is that preferred we shall describe the process applied to it. This kind of gilding requires the following successive operations : 1. Preparation of the Watch Parts. Coming from the hands of the watchmaker, they preserve the marks of the file, which are obliterated by rubbing upon a wet stone, and lastly upon an oil- stone. 2. The oil or grease which soils them is removed by boiling the GILDING WATCH MOVEMENTS. 189 watch parts for a few minutes in an alkaline solution made of 100 parts of water and 10 of caustic soda or potassa, and rinsing them in clean water, which should wet them thoroughly if all the oil has been removed. The articles are threaded upon a brass wire. 3. A few gilders then cleanse them rapidly by the compound acids for a bright lustre ; others simply dry them carefully in sawdust from white wood. 4. Holding the Parts. The parts thus prepared are fastened by means of brass pins with flat heads upon the even side of a block of cork. 5. The parts thus held upon the cork are thoroughly rubbed over with a brush quite free from greasy matters, and charged with a paste of the finest pumice-stone powder and water. The brush is made to move in circles in order not to abrade one side more than the other. The whole is thoroughly rinsed in clean water, and no particle of pumice dust should remain upon the pieces of the cork. 6. Afterwards we plunge the cork and all into a mercurial solution, which very slightly whitens the copper, and is composed of Water . . . * , ,;~ . 10 litres. Nitrate of binoxide of mercury . 2 grammes. Sulphuric acid , _,: j ; . 4 The pieces are simply passed through the solution, and then rinsed. This operation, which too many gilders neglect, gives strength to the graining, which without it possesses no adherence, especially when the watch parts are made of white German silver, dignified by the name of nickel by watchmakers, or when the baths contain tin in their composition. 7. Graining. In this state the parts are ready for the graining that is to say, a silvering done in a particular manner. Nothing is more variable than the composition of the graining pow- ders ; and it may be said that each gilder has his own formula, accord- ing to the fineness of the grain desired. The following formulae are used in the works of M. Pinaire : Silver in impalpable powder. . . .30 grammes. Bitartrate of potassa (cream of tartar) finely pulverised and passed through a silk sieve 300 Chloride of sodium (common salt) pulver- ised and sifted as above i kilogramme. It is stated that the majority of operators, instead of preparing their graining -silver, prefer buying the Nuremburg powder, which is produced by grinding a mixture of honey and silver-foil with a muller igO ELECTRO-DEPOSITION OF GOLD. upon a ground -glass plate, until the proper fineness is obtained. The silver is separated by dissolving the honey in boiling water, and wash- ing the deposited metal in a filter until there is no remaining trace of honey. The silver is then carefully dried at a gentle heat. This silver, like bronze powder, is sold in small packages : Silver powder 30 grammes. Cream of tartar . . . . 120 to 150 Common salt (white and clean) . . . 100 Or Silver powder 30 Cream of tartar 100 Common salt i kilogramme. All these substances should be as pure as possible, and perfectly dry. Cream of tartar is generally dry, but common salt often needs, before or after it has been pulverised, a thorough drying in a porcelain or silver dish, in which it is kept stirred with a glass rod or a silver spoon. The mixture of the three substances must be thorough, and effected at a moderate and protracted heat. The graining is the coarser as there is more common salt in the mixture ; and conversely, it is the finer and more condensed as the proportion of cream of tartar is greater ; but it is then more difficult to scratch-brush. 8. The Graining Proper. This operation is effected as follows : A thin paste of one of the above mixtures with water is spread by means of a spatula upon the watch parts held upon the cork. The cork itself is fixed upon an earthenware dish, in which a movement of rotation is imparted by the left hand. An oval brush with close bristles is held in the right hand, and rubs the watch parts in every direction, but always with a rotary motion. A new quantity of the paste is added two or three times, and rubbed in the manner indicated. The more we turn the brush and the cork, the rounder becomes the grain, which is a good quality ; and the more paste we add, the larger the grain. The watchmakers generally require a fine grain, circular at its base, pointed at its apex, and close that is to say, a multitude of juxtaposed small cones. A larger grain may, however, have a better appearance, but this depends on the nature and the size of the articles grained. 9. When the desired grain is obtained, the watch parts are washed and then scratch-brushed. The wire brushes employed also come from Nuremburg, and are made of brass wires as fine as hair. As these wires are very stiff and springy, they will, when cut, bend and GILDING WATCH MOVEMENTS. 19! turn in every direction, and no work can be done with them. It is, therefore, absolutely necessary to anneal them more or less upon an even fire. An intelligent worker has always three scratch-brushes annealed to different degrees : one which is half soft, or half annealed, for the first operation of uncovering the grain ; one harder, or little annealed, for bringing up lustre ; and one very soft, or fully annealed, used before gilding, for removing the erasures which may have been made by the preceding tool, and for scratch-brushing after the gild- ing. Of course the scratch -brushing operation, like the graining proper, must be done by striking circles, and giving a rotary motion between the fingers to the tool. The cork is now and then made to revolve. After a good scratch-brushing, the grain, seen through a magnifier, should be regular, homogeneous, and with a lustre all over. Decoctions of liquorice, saponaire (soapwort), or Panama wood are employed in this operation. CHAPTER XV. VARIOUS GILDING OPERATIONS. Electro-gilding Zinc Articles. Gilding Metals with Gold Leaf.--Cold Gild- ing. Gilding Silk, Cotton, &c. Pyro-gilding. Colour of Electro- deposited Gold. Gilding in various Colours. Colouring Processes. Re- colouring Gold Articles Wet-Colour Process. French Wet-Colouring. London Process of Wet-Colouring. Electro-gilding Zinc Articles. About thirty years ago a very important industry was introduced into France, which at once com- manded universal admiration, and a rapid sale for the beautiful pro- ducts which were abundantly sent into the market. We allude to the so-called electro-bronzes. These exquisite works of art, many of which would would bear comparison with the finest of real bronzes, were in fact zinc castings or copies from original works of high merit, coated with brass, or, as it was then called, electro-bronze, and artificially coloured, so as to imitate as closely as possible the characteristic tone of real bronze. At the time we speak of, articles of every conceivable form, from the stag beetle, mounted upon a leaf, electrotyped from nature, and reproduced in the form of a zinc casting, each object being electro -bronzed, to a highly-finished statuette or massive candelabrum, appeared in our shop windows and show-rooms, and presented a really beautiful and marvellously varied and cheap addition to our rather meagre display of art metal work. It was soon discovered by those who had the taste for possessing bronzes, but not the means to satisfy it, that the imitation bronzes lacked nothing of the beauty of the originals, while they presented the advantage of being remarkably cheap, and thus within the reach of many. The process by which the electro -bronzing upon zinc castings is conducted is considered in another place, and we will now explain how .articles of this description, that is zinc castings, may be electro -gilt, and either a bright or dead surface imparted to the work according to the artistic requirements of the article to be treated. Preparation of Zinc Castings for Gilding. In order to obtain the best possible results, the zinc casting presuming it to be a work of art which deserves the utmost care to turn it out creditably should first be examined for air or sand-holes, and these, if present, must be ELECTRO-GILDING ZINC ARTICLES. 193 stopped or plugged with easy-running pewter solder, and the spot afterwards touched up so as to resemble the surrounding surface, whether it be smooth or chased. When the whole article has been carefully examined and treated in this way, it is to be immersed for a few minutes only in a moderately strong potash bath, after which it must be well rinsed. It is next to be placed in a weak sulphuric acid pickle, consisting of Sulphuric acid .... 10 parts Water . ... ... /^ 100 but should not remain in the acid liquor more than a minute or two, after which it is to be thoroughly well rinsed in clean water. The article, having a copper wire attached, is now to be placed in either a cold or warm brassing solution or alkaline coppering bath for a short time, or until it is covered with a thin deposit of either metal. If on removing it from the brassing bath it is found that the soldered spots have not received the deposit, and present a blackish appearance, the article must be well scratch-brushed all over, and again placed in the bath, which, by the way, will deposit more readily upon the solder if the bath be warm, a brisk current employed, and gentle motion given to the article when first placed in the bath. The object, when placed in the bath a second time, should be allowed to remain therein for about half an hour or somewhat longer, by which time, if the solution be in good order, and the current sufficiently active, it will yield a deposit sufficiently thick either for bronzing or gilding. It is a common practice to deposit a slight coating of brass or copper upon zinc-work in a warm solution in the first instance, and then to complete the operation in a cold bath. When the object is to be left bright, that is merely scratch -brushed, after being coated with copper or brass as above, it is simply gilt in an ordinary cyanide gilding bath, and is then treated in the same way as ordinary brass or copper work. If, however, the article is to be left dead, the following method may. be adopted : After being well rinsed, the object is to be immersed in a silvering bath in which it is allowed to remain until it assumes the characteristic white and dead lustre of electro -deposited silver. When the desired effect is produced, the article must be well rinsed in warm (not hot) water and immediately placed in a gilding bath which is in a good condition for yielding a deposit of the best possible colour. Another method, which has been much practised on the Continent, is thus described byRoseleur: "Add to the necessary quantity of water one -tenth of its volume of sulphuric acid, and dissolve in this acid liquor as much sulphate of copper as it will take up at the ordinary temperature. This solution will mark from 20 to 24 Baume 194 VARIOUS GILDING OPEEATIONS. (about I 1600) ; now add' water to reduce its specific gravity to 16 or 18 B. (about 1-1260). This galvano -plastic * bath is generally contained in large vessels of stoneware, slate, wood, or gutta-percha, and porous cells are immersed in it, which are filled with a weak solution of sulphuric acid and amalgamating salts. Plates or cylinders of zinc are put into these cells, and are connected with one or more brass rods, which rest upon the sides of the vat, and support the articles which are to receive the dead lustre." The articles of zinc, previously coated with copper or brass in an alkaline solution, are suspended in the above bath until they have acquired the necessary dead lustre, after which they are treated as follows : After being thoroughly well rinsed, they are immersed for a moment in a bath composed of Nitrate of mercury . . i part Sulphuric acid ~~ j , .' . . 2 parts Water 1,000 After again rinsing, the articles are steeped in the following solu- tion : Cyanide of potassium ... 40 parts Nitrate of silver 10 Water 1,000 The articles are well rinsed after removal from this bath, and are then ready for gilding, the solution recommended for which is com- posed of Phosphate of soda .... 60 parts . Bisulphite of soda . . . . 10 Cyanide of potassium . . , i to 2 parts Neutral chloride of gold . . . 2 parts Water ...... 1,000 This bath is used at nearly the boiling point, with an intense voltaic current. The anode consists of platinum wire, which at first is dipped deeply into the solution, and afterwards gradually raised out of the bath, as the article becomes coated with gold, until, towards the end of the operation, but a small surface of the wire remains in the bath. It is said that the colour of the gilding by this method is remarkable for its " freshness of tone." Some operators first gild the article by the dipping process before described, and then deposit the requisite quantity of gold to produce a dead surface by the electro process in a bath specially suited to the purpose. Other gilders first half -gild the * This term, though never a correct one, is still generally used on the con- tinent to designate the art of electrotyping, or the deposition of copper from its sulphate. GILDING METALS WITH GOLD LEAF. 195 article with the battery, then dip it in the mercury bath, and after well rinsing, finish the operation by a second deposit of gold. In either case, the article is finally well rinsed in warm water, and after- wards dried in hot sawdust or a warm stove. Great care is taken to avoid handling the article so as not to stain it with the fingers, or to scratch it in any way, since the delicate frosted surface is very readily injured. It is also very important that the rinsing, after each opera- tion, should be perfectly carried out, and that the final drying is complete ; for if any of the gold solution remain upon any part of the work, voltaic action will be set up between the zinc and copper at the spot, and the article disfigured by the formation of verdigris. The foregoing process is specially applied to articles of zinc, such as clock- cases, &c., which are generally kept under glass, but may be applied to smaller ornamental articles which are not liable to friction in use. In our own practice we have found when gilding zinc, that the best results were obtained when all the various stages of the process, from the first pickling to the drying, were conducted with rapidity, the greatest possible attention being devoted to the various rinsing opera- tions. If all baths are in proper order, the various dips and electro - deposits should each only occupy from a few seconds to a few minutes, while the drying should be effected with the greatest possible despatch, so that the object, being but thinly coated with metals which are electro -negative to itself, may not be subjected to electro -chemical action in parts owing to the presence of moisture or traces of the gilding solution. Gilding Metals with Gold Leaf. Articles of steel are heated until they acquire a bluish colour, and iron or copper are heated to the same degree. The first coating of gold leaf is now applied, which must be gently pressed down with a burnisher, and again exposed to gentle heat ; the second leaf is then applied in the same way, followed by a third, and so on ; or two leaves may be applied instead of one, but the last leaf should be burnished down while the article is cold. Cold Gilding. A very simple way of applying this process is to dissolve half a pennyweight of standard gold in aqua regia ; now steep several small pieces of rag in the solution until it is all absorbed ; dry the pieces of rag, and then burn them to tinder. To apply the ashes thus left, rub them to a powder, mix with a little water and common salt, then dip a cork into the paste thus formed, and rub it over the article to be gilt. Gilding Silk, Cotton, &c. There are several methods by which textile fabrics may be either gilt or silvered. One method is to stretch the fabric tightly upon a frame, after which it is immersed in a solution of acetate of silver, to which ammonia is added until the pre- cipitate at first formed becomes dissolved, and a clear solution obtained. 196 VAEIOUS GILDING OPEKATIONS. After immersion in this solution for an hour or two, the thread or fabric is first dried, and then submitted to a current of hydrogen gas, by which the silver becomes reduced and the surface metallised. In this condition it is a conductor of electricity, and may be either gilt or silvered in any ordinary cyanide solution. By another method, the piece of white silk is dipped in an aqueous solution of chloride of gold ; it is then exposed to the fumes of sulphurous acid gas, pro- duced by burning sulphur in a closed box, when in a very short time the entire piece will be coated with the reduced metal. Fyro-gilding. This process, which is recommended for coating iron and steel, is conducted upon the same principle as pyro-plating, except that the precious metal is deposited in several layers, instead of, as in the former case, depositing the required coating in one operation. The steel article being prepared as recommended for pyro-plating, first receives a coating of gold in the gilding-bath ; it is next heated until the film of gold disappears ; it is then again gilt, and heated as before, these operations being repeated until the last layer remains fully on the surface. Colour of Electro-deposited Gold. It might readily be imagined that gold, when deposited from its solution upon another metal, would necessarily assume its natural colour, that is, a rich orange yellow. That such is not the case is well known to all who have practised the art of gilding, and the fact may easily be demonstrated by first gilding a piece of German silver in a cold cyanide solution of gold, and then raising the temperature of the solution to about 130 Fahr. If now a similar piece of metal be gilt in the warm solution, and the two gilt surfaces compared, it will be found that while the deposit from the cold solution is of a pale yellow colour, that obtained by the warm solution is of a deeper and richer hue. The colour of the deposit may also be influenced by the nature of the current, the same solution being use"d. For example, the gold deposited by the current from a Bunsen battery is generally of a finer and deeper colour than that obtained by the Wollaston battery. In the former case, the superior intensity of the current seems to favour the colour of the deposit. This difference, however, is not so strongly marked in the case of some other gold solutions, as that prepared by precipitating gold with sulphide of ammonium, and redissolving the precipitate with cyanide, for example, which yields an exceedingly good coloured deposit with copper and zinc elements (Wollaston or Daniell). Since the colour of the gold deposit is often of much importance to the electro -gilder, we purpose giving below the various means adopted for varying the colour of the deposit to suit the requirements of what we may terra, fancy gilding. Gilding in Various Colours. A very deep coloured deposit of GILDING IN VARIOUS COLOURS. 197 gold may be obtained in an old gold solution, in which organic matter has accumulated from imperfect rinsing of the work after scratch - brushing, and in which there is a good proportion of free cyanide, by employing a strong current and exposing a large surface of anode. In this case the deposit is of &foxij colour, as it is termed, and when scratch -brushed exhibits a depth of tone which, while being unsuited for most purposes, may be useful as a variety in some kinds of fancy gilding where a strong contrast of colours is a requisite. The colour of the deposit is also much influenced, as before observed, by the extent of anode surface exposed in the bath during the operation of gilding ; if a larger surface be exposed than is propor- tionate to the cathode surface (or work being gilt) the colour is dark, whereas when the anode surface exposed is below the proper propor- tion, the deposit will be of a pale colour. Motion also affects the colour of the gold deposit sometimes in a very remarkable degree the colour being lighter when the article is moved about in the solution, and darker when allowed to rest. These differences are more marked, however, with old and dark coloured solutions than with recently prepared solutions, or such as have been kept scrupulously free from the introduction of organic impurities. For ornamental gilding, as in cases where chased or engraved silver or plated work is required to present different shades of colour on its various surfaces, solutions of gold may be prepared from which gold of various tints may be obtained by electro-deposition. These solu- tions are formed by adding to ordinary cyanide gilding baths vary- ing proportions of silver or copper solution, or both, as also solutions of other metals ; but in order to insure uniformity of results, the solu- tions should be worked with anodes formed from an alloy of the same character ; or at least, if an alloy of silver and gold, for example, is to be deposited, an anode of gold and one of silver should be employed in order to keep up the condition of the compound solution. Green Gold. This is obtained by adding to a solution of double cyanide of gold and potassium a small proportion of cyanide of silver solution, until the desired tint is obtained. The solution should be worked cold, or nearly so. Eed Gold. To a solution of cyanide of gold add a small quantity of cyanide of copper solution, and employ a moderately strong current. It is best, in making these additions, to begin low, by adding a very small proportion of the copper solution at first, and to increase the quantity gradually until the required tone is obtained, since an excess of the copper solution would produce a deposit of too coppery a hue. The tint generally required would be that of the old-fashioned gold and copper alloy with which the seals and watch cases of the last, and earlier part of the present, century were made. 198 VAEIOUS GILDING OPERATIONS. Pink Gold. This may be obtained by first gilding the article in the usual way, then depositing a slight coating in the preceding bath, and afterwards depositing a mere pellicle of silver in the silvering bath. The operation requires great care to obtain the desired pink tint. The article is afterwards burnished ; but since the silver readily becomes oxidised (unless protected by a colourless varnish) the effect will not be of a permanent character. Pale Straiv -coloured Gold. Add to an ordinary cyanide solution a small quantity of silver solution, and work the compound solution cold, with a small surface of anode and a weak current. Colouring Processes. When the gilding is of an inferior colour it is sometimes necessary to have at command some method by which the colour may be improved. There are several processes by which this may be effected, but in all cases there must be a sufficient coating of gold upon the article to withstand the action of the materials employed. This condition being fulfilled, the artificial colouring processes may be applied with advantage, and gold surfaces of great beauty obtained. Of the processes given below, the first formula will be found exceedingly useful, since it may be applied to work which, though fairly well gilt, need not be so stoutly coated as is" necessary when employing the second formula. It is specially useful for bringing up a good colour upon brooches, albert chains, and small articles generally. It is technically known by the name ''green colour," and is composed as follows : ozs. dwts. gra. I. Sulphate of copper ...020 French verdigris . . . o 412 Sal ammoniac ....040 Nitre 040 Acetic acid (about) i o o The sulphate of copper, sal ammoniac, and nitre are first to be pulver- ised in a mortar, when the verdigris is to be added and well mixed with the other ingredients. The acetic acid is then to be poured in, a little at a time, and the whole well worked up together, when a thin mass of a bluish green colour will result. The article to be coloured is to be dipped in the mixture and then placed on a clean piece of sheet copper, which is next to be heated over a clear fire, until the compound assumes a dull black colour ; it is now allowed to cool, and is then plunged into a tolerably strong sulphuric acid pickle, which soon dissolves the colouring salts, leaving the article of a fine gold colour. It is generally advisable to well scratch-brush the article before colouring, when it will come out of the pickle perfectly bright. When removed from the pickle, the article must be well rinsed in hot water, to which a small quantity of carbonate of KECOLOURING GOLD ARTICLES. 1 99 potash should be added ; it should next be brushed with -warm soap and -water, a soft brush being employed, and again rinsed in hot water, after which it may be placed in warm box sawdust, being- finally brushed with a long-haired brush. II. When the work is strongly gilt, but of an indifferent colour, the following mixture may be used : Powdered alum . . . . 3 ounces nitre . . . . ' 6 sulphate of zinc 3 common salt 3 ,. These ingredients are to be worked up into a thickish paste, and the articles brushed over with it ; they are then to be placed on a piece of sheet iron, and heated over a clear charcoal or coke fire until they become nearly black ; when cool they are to be plunged into dilute muriatic or sulphuric acid pickle. Recolouring Gold Articles. It not unfrequently happens that an electro -gilder is required by his customers to renovate articles of gold jewellery, so as to restore them to the original condition in which they left the manufacturers. Although it has been the common practice, with some electro-gilders, to depend upon their baths to give the desired effect to what is called " coloured " jewellery, in some cases it would be better to apply the methods adopted by goldsmiths and jewellers for this purpose, by which the exact effect required can be more certainly obtained. There are two methods of colouring gold articles; namely, "dry colouring," which is applied to articles made from 1 8 -carat gold and upwards, and "wet-colour- ing," which is adopted for alloys of gold below that standard, but seldom lower than 12 -carat. The mixture for dry-colouring is composed of Nitre . . . , , ., . 8 ouncei Alum . . . ... 4 Common salt 4 16 Or the following : Sal ammoniac . . . . . 4 ounces Saltpetre . . . . . 4 Borax 4 12 The ingredients must first be reduced to a powder, and then put into an earthen pipkin, which is to be placed over a slow fire to allow the salts to fuse gradually; to assist this, the mixture should b 2OO VAEIOUS GILDING OPERATIONS. stirred with an iron rod. When the fused salts begin to rise in the vessel, the pieces of work, suspended by a fine silver or platinum wire, should be at once immersed, and kept moved about until the liquid begins to sink in the colouring-pot, when the work must be removed, and plunged into clean muriatic acid pickle, which will dissolve the adhering salts. The colouring mixture will again rise in the pot, after the withdrawal of the work, when it may be reimmersed (when dry) for a short time, and then pickled as before ; it is then to be . rinsed in a weak solution of carbonate of soda or potash, and after- wards well washed in hot soda and water, next in clean boiling water, and finally put into warm box sawdust to dry. Previous to colouring the work, it should be highly polished or burnished, although the latter operation may be performed after the work has been coloured ; the former method is, however, the best, and produces the most pleasing effect. ffiet-colouring Process. This is applied to gold articles made from alloys below 1 8 -carat, and though there are many formulae adopted for colouring gold of various qualities below this standard, we must limit our reference to ojie^or two only, and for ample infor- mation upon this subject dra$C the reader's attention to Mr. Gee's admirable Goldsmith's HjmSboJc* The ordinary "wet colour," as the jewellers term it, ^jfsists chiefly in adding a little water to the ingredients formerly gi^en, the proportions of the salts being gene- rally about the sameY that is, nitre 8 ounces, alum and common salt of each 4 ounces. \jrtiese ingredients being reduced to a fine powder and mixed together, are worked up into a thick paste with a little hot water in a good- sized pipkin or crucible, which is placed over a slow fire and heated gradually, the mixture being stirred with a wooden spoon until it boils up. The work is now to be introduced as before and allowed to remain for several minutes, when it must be withdrawn and plunged into boiling water, which will dissolve the colouring salts and show how far the colouring has progressed. When the mixture exhibits a tendency to boil dry, an occasional spoonful of hot water must be added to thin it, but never while the work is in the pot. When the work is first put into the colour it becomes nearly black, but assumes a lighter tone after each immersion until the characteristic colour of fine gold is obtained. When the operation is complete, the work will bear a uniform appearance, though somewhat dead, and may be brightened by burnishing or scratch-brushing. After each dipping the work must be well rinsed in clean boiling water. It must be finally plunged into hot water, and, after weU shaking, be put into warm boxwood sawdust. * " The Goldsmith's Handbook," by George E. Gee, 2nd edition, 1881. Crosby Lockwood and Co. RECOLOURING GOLD ARTICLES. 2OI French Wet Colouring. The formula for this is : Saltpetre 8 ounces Common salt ..... 4 Alum . . .... . . 4 The ingredients must be finely pulverised, as before, and intimately mixed ; they are then to be put into a good-sized pipkin or crucible, and sufficient hot water added to form the whole into a thick paste. The mixture should be slowly heated, and stirred with a wooden spoon, when it will soon boil up. The work is then to be immersed for several minutes, then withdrawn and plunged into boiling water, which, dissolving the salts, will allow the work to be examined, when, if not of a sufficiently good colour, it must be reimmersed for a short time. As the mixture thickens by evaporation small quantities of boiling water must be added occasionally, but only after the work has been withdrawn. On the first immersion the work assumes a blackish colour, but at each successive immersion it becomes lighter, as the baser metals become removed from the surface of the work, until it finally assumes the characteristic colour of fine gold. This process should be applied to gold of less than 16 carats. London Process of Wet Colouring. For gold of not less than 15 carats the following mixture is used : Nitre . . . v .. . , 15 ounces Common salt . . . - ..*,, -. . 7 Alum . . ; . ' .' . 7 Muriatic acid . . - . .. . . i 30 The salts are to be powdered, as before ; into a crucible about 8 inches high and 7 inches in diameter, put about two spoonfuls of water, then add the salts, place the crucible on the fire, and heat gradually until fusion takes place, keeping the mixture well stirred with a wooden spoon. The article, which should first be boiled in nitric acid pickle, is then to be suspended by a platinum wire, and immersed in the fused mixture for about five minutes, then withdrawn and steeped in boiling water. The muriatic acid is now to be added to the mixture, and when it again boils up the article is to be immersed for about five minutes, then again rinsed in boiling water. A spoon- ful of water is now to be added to the mixture, and the work again put in for about three minutes, and again rinsed ; now add two spoon- fuls of water to the mixture, boil up, and immerse the work for two minutes, and rinse again. Finally, add about three spoonfuls of water, and, after boiling up, put in the work for one minute, then rinse in abundance of clean boiling water, when the work will present a beau- tiful colour. The work should then be rinsed in a very dilute hot solution of potash, and again in clean boiling water, after which it should be placed in clean, warm boxwood sawdust. CHAPTER XVI. MERCURY GILDING. Preparation of the Amalgam. The Mercurial Solution. Applying the Amalgam Evaporation of the Mercury. Colouring. Bright and Dead Gilding in Parts Gilding Bronzes with Amalgam. Ormoulu Colour. -Red-Gold Colour. Ormoulu. Red Ormoulu. Yellow Ormoulu. Dead Ormoulu. Gilders' Wax. Notes on Gilding. ALTHOUGH the process of gilding metals with an amalgam of gold and mercury, or quicksilver, is not, strictly speaking, an electro -chemical art, it is important that this system of gilding should be known to the electro -gilder for several reasons : it is the chief process by which metals were coated with gold before the art of electro -gilding was introduced ; it is still employed for certain purposes, and many arti- cles of silver which have been mercury gilt occasionally come into the electro-depositor's hands for regilding, and which are sometimes specially required to be subjected to the same process, when the voltaic method is objected to. Mercury-gilding, formerly called wash-gilding, water-gilding, or amalgam-gilding, essentially consists in brushing over the surface of silver, copper, bronze, or brass, an amalgam of gold and quicksilver, and afterwards volatilising the mercury by heat. By repeated appli- cations of the amalgam and evaporation of the mercury, a coating of gold of any desired thickness may be obtained, and when properly carried out the gilding by this method is of a far more durable character than that obtained by any other means. As we have before observed, the process, unless conducted with great care, is a very unhealthy one, owing to the deleterious nature of the fumes of mer- cury to which the workmen are exposed, if these are not properly carried off by the flue of a suitable furnace. Preparation of the Amalgam. Mercury, as is well known, has the peculiar property of alloying or amalgamating itself with gold, silver, and some other metals and alloys, with or without the aid of heat. To prepare the amalgam of gold for the purpose of mercury gilding, a weighed quantity of fine or standard gold is first put into a crucible and heated to dull redness. The requisite proportion of mercury 8 parts to I part of gold is now added, and the mixture is APPLYING THE AMALGAM. 203 stirred with a slightly crooked iron rod, the heat being kept up until the gold is entirely dissolved by the mercury. The amalgam is now to be poured into a small dish about three parts filled with water, in which it is worked 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 acquires a pasty condition capable of receiving the impression of the fingers. The amalgam is afterwards to be squeezed 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 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 very important that the mercury employed for this purpose be pure. The gold employed may be either fine or standard, but water- gilders generally use the metal alloyed either with silver or copper ; if to be subjected to the after process of colouring, standard alloys should be employed, since the beauty of the colouring process depends upon the removal, chemically, of the inferior metals, silver, copper, or both, from the alloy of gold, leaving the pure metal only upon the surface. The amalgam is crystalline, and produces a peculiar crackling sound when pressed between the fingers close to the ear. It is usual to keep a moderate supply of gold amalgam in hand when mercury- gilding forms part of the gilder's ordinary business, and the compound is divided into a series of small balls, which are kept under water ; it is not advisable, however, to allow the amalgam to remain for a long period before being employed, since a peculiar phenomenon known as liquation takes place, by which the amalgam loses its uniformity of composition, the gold being more dense in some parts than in others. The Mercurial Solution. To apply the amalgam, a solution of nitrate of mercury is employed, which is prepared by dissolving, in a glass flask, 100 parts of mercury in no parts of nitric acid of the specific gravity 1-33, gentle heat being applied to assist the chemical action. The red fumes which are given off during the decomposition must be allowed to escape into the chimney, since they are highly deleterious when inhaled. When the mercury is all dissolved, the solution is to be diluted with about 25 times its weight of distilled water, and bottled for use. Applying the Amalgam. The pasty amalgam is spread with the blade of a knife, upon a hard and flat stone called the gilding stone, and the article, after being well cleaned and scratch-brushed, is treated in the following way : the gilder takes a small scratch - brush, formed of stout brass wire, which he first dips in the* solution 204 MERCURY GILDING. of nitrate of mercury, and then next draws it over the amalgam, by which it takes up a small quantity of the composition , he then passes the brush carefully over the surface to be gilt, repeatedly dipping the brush in the mercurial solution and drawing it over the amalgam until the entire surface is uniformly and sufficiently coated. The article is afterwards well rinsed and dried, when it is ready for the next operation. Evaporation of the Mercury. For this purpose a charcoal fire, resting upon a cast-iron plate, has been generally adopted, a simple hood of sheet iron being the only means of partially protecting the workmen from the injurious effects of the mercurial vapours. M. D'Arcet, of Paris, invented a furnace, or forge, with an arrangement by which the workman could watch the progress of his work through glass, and thus escape the injurious effects of the mercury vapours. The difficulty of seeing the process clearly, howe/er, during the more important stages of the operation (owing doubtless to the condensa- tion of the mercurial vapour upon the glass), caused the arrangement to be disapproved by those for whose well-being it was specially designed, and the simple hood, regardless of its fatal inadequacy, is still preferred by many mercury gilders. When the amalgamated article is rinsed and dried, the gilder exposes it to the glowing char- coal, turning it about, and heating it by degrees to the proper point ; he then withdraws it from the fire by means of long pincers or tongs, and takes it in his left hand, which is protected with a leather or padded glove, and turns it over the fire in every direction, and while the mercury is volatilising, he strikes the work with a long-haired brush, to equalise the amalgam coating, and to force it upon such parts as may appear to require it. When the mercury has become entirely volatilised, the gilding has a dull greenish-yellow colour, and the workman examines it to ascer- tain if the coating is uniform ; if any bare places are apparent, these are touched up with amalgam, and the article again submitted to the fire, care being taken to expel the mercury gradually. Colouring. The article is next well scratch-brushed, when it assumes a pale greenish colour ; it is afterwards subjected to another heating to expel any remaining mercury, when, if sufficient amalgam has been applied, it acquires the characteristic orange -yellow colour of fine gold. It is next submitted to the process of colouring. If required to be bright, the piece of work is burnished in the ordinary way, or, according to the nature of the article, is subjected to the ormoulu process described further on. When the surface is required to be dead, or frosted, the article is treated somewhat in the same way as " dry coloured" gold jewellery work, that is, it is brushed over with a hot paste composed of common salt, nitre, and alum, fused in BRIGHT AND DEAD GILDING IN PAETS. 205 the water of crystallisation of the latter, after which it is heated upon a brisk charcoal fire, without draft, and moved about. until the salts become first dried and then fused ; the article is then plunged into a vessel containing a large quantity of cold water, in which the colour- ing salts are dissolved, and the dead or matted appearance of the work becomes at once visible. When applying the amalgam for dead gilding, great care must be exercised to insure a sufficiently stout coating of gold upon the work, otherwise the colouring salts will surely attack the underlying metal. When about to colour the work as above, the operator binds the article by means of iron wire to a short rod of the same metal ; he then either dips the article in the colouring paste or applies it with a brush, and after gently drying it, holds the piece over the fire until the perfect fusion of the composition has taken place, when it is at once dipped in water. The coloured marks left by the wire are removed by a weak solution of nitric acid. Bright and Dead Gilding in Farts. When it is desired to have some parts of an article burnished and other parts left dead, the former are protected by a mixture of Spanish white (pure white chalk), bruised sugar candy, and either gum or glue, dissolved in water. The mixture of alum, nitre, and common salt is then applied to the parts to be left dead, the article afterwards dried, and heated over the char- coal fire as before until the dried salts have been fused, when it is at once plunged into cold water, and subsequently in dilute nitric acid, being finally well rinsed and dried. The protected parts are then subjected to the operation of burnishing, when the article is complete. Another method adopted in France, in which electro -gilding takes a part, is described as follows : Those parts which are intended for a dead lustre are first gilt with the amalgam ; the article is then heated, scratch -brushed, and re -heated to the orange -yellow colour. Then, with the battery, a sufficiently strong gold deposit is given to the whole, without regard to the parts already mercury-gilt. All the surfaces are next carefully scratch-brushed, and the electro-gilt por- tions are brushed over, first with a thin mixture of water, glue, and Spanish white, and afterwards with a thick paste of yellow clay. After drying, the mercury-gilt portions are covered with the paste for dead-gilding (alum, nitre, &c.), and the article heated until the salts fuse, when it is plunged into water and treated as above. Roseleur, however, considers this method open to several objections, among which is, red spots are apt to be produced upon such places as may have been too much heated, or where the gold has not been suffi- ciently thick. He recommends the following by preference : " Gild with amalgam, and bring up the dead lustre upon those portions which are to receive it, and preserve [protect] them entirely with a stopping -off varnish. After thorough drying, cleanse the object by 206 MERCURY GILDING. dipping it into acids in the usual manner, and gild in the electro - bath. The varnish withstands all these acids and solutions. When the desired shade is obtained, dissolve the varnish with gazoline or benzine, which, unless there has been friction applied, do not injure in any way either the shade or velvety appearance of the dead lustre. Wash in a hot solution of cyanide of potassium, then in boiling water, and allow to dry naturally. . . . Gilding with dead lustre, whatever process be employed, suits only those objects which will never be sub- jected to friction ; even the contact of the fingers injures it." Gilding Bronzes with Amalgam. The article is first annealed very carefully, as follows : The gilder sets the piece upon burning charcoal, or peat, which yields a more lively and equal flame, covering it up so that it may be oxidised as little as possible, and taking care that the thinner parts do not receive an undue amount of heat. This operation is performed in a dark room, so that the workman may see when the desired cherry -red heat is reached. He then lifts the piece from the fire, and sets it aside to cool in the air gradually. When cold, the article is steeped in a weak sulphuric acid pickle, which removes or loosens the coating of oxide. To aid this he rubs it with a stiff and hard brush. When the article has been thus rendered bright, though it may appear uniform, it is dipped in nitric acid and rinsed, and again rubbed with a long-haired brush. After washing in clean water, it is dried in hot sawdust or bran. This treatment somewhat reduces the brightness of the surface, which is favour- able to the adhesion of the gold. The amalgam is next applied with the scratch-brush, as before, and the object then heated to expel the mercury. If required to be dead, it is treated with the colouring - salts, as before described. Ormoulu Colour. To obtain this fine colour upon bronze or other work, the gilt object is first lightly scratch-brushed, and then made to come back again, as it is termed, by heating it more strongly than if it were to be left dead, and then allowed to cool a little. The ormoulu colouring is a mixture of hematite (peroxide of iron), alum, and sea- salt, made into a thin paste with vinegar, and applied with a brush until the whole of the gilded surface is covered, except such parts as are required to be burnished. The object is then heated until it begins to blacken, the proper heat being known by water sprinkled over it producing a hissing noise. It is next removed from the fire, plunged into cold water, and washed, and afterwards rubbed with a brush dipped in vinegar if the object be smooth, but if it be chased, dilute nitric acid is employed for this purpose. The article is finally washed in clean water, and dried at a gentle heat. Bed Gold Colour. To produce this colour, the composition known as gilders' wax is used. The article, after being coated with amalgam, ORMOULU. 207 is heated, and while still hot is suspended by an iron wire, and coated with gilders' wax, a composition of beeswax, red ochre, ver- digris, and alum. It is then strongly heated over the flame of a wood fire ; sometimes small quantities of the gilders' wax are thrown into the fire to promote the burning of the fuel. The object is turned about in every direction, so as to render the action of the heat uni- form. As soon as all the wax has become burnt off, the flame is put out, and the article plunged into cold water, well washed, and brushed over with a scratch-brush and pure vinegar. Should the colour not be uniform or sufficiently good, the article must be coated with verdigris dissolved. in vinegar, dried over a gentle fire, then plunged into cold water and brushed over with vinegar ; and if the colour is of too deep a tone, dilute nitric acid may be substituted for the vinegar. After well washing, the article is burnished, then again washed, and finally wiped with soft linen rag, and lastly dried at a gentle heat. Orxnoulu. The beautiful surface noticeable on French clocks and other ornamental work is produced by the process called ormoulu. The article is first gilt, and afterwards scratch-brushed. It is then coated with the thin paste of saltpetre, alum, and oxide of iron before mentioned, the ingredients being reduced to a fine powder, and worked up into a paste with a solution of saffron, annatto, or other colouring matter, according to the tint required, whether red or yellow. When the gilding is strong, the article is heated until the coating of the above mixture curls over by being touched with a wet finger. But when the gilding is only a slight film of gold, the mix- ture is merely allowed to remain upon the article for a few minutes. In both cases, the article is quickly washed with warm water containing in suspension a certain quantity of the materials referred to. The article must not be dried without washing. Such parts as may have acquired too deep a colour are afterwards struck with a brush made with long bristles. By a series of vertical strokes with the brush the uniformity of surface is produced. If the first operation has not been successful, the colouring is removed by dipping the article in dilute sulphuric acid, and after well rinsing, the operation is repeated until the desired effect is obtained. Red Ormoulu is produced by employing a mixture composed of alum and nitre, of each 30 parts ; sulphate of zinc, 8 parts ; common salt, 3 parts ; red ochre, 28 parts ; and sulphate of iron, I part. To this may be added a small quantity of annatto, madder, or other colouring matter, ground in water. Yellow Ormoulu is produced by the following: red ochre, 17; potash alum, 50 ; sulphate of zinc, 10 ; common salt, 3 ; and salt- petre 20 parts, made up into a paste as before. 208 MERCUEY GILDING. Dead Ormoulu, for clocks, is composed of saltpetre, 37 ; alum, 42 ; common salt, 12 ; powdered glass and sulphate of lime, 4 ; and water, 5 parts. The whole of these substances are to be well ground and mixed with water. Gilders 1 Wax, for producing a rich colour upon gilt work, is made from oil and yellow wax, of each 25 parts ; acetate of copper, 13 parts ; and red ochre, 37 parts. The oil and wax are to be united by melt- ing, and the substances, after being well pulverised, added gradually. Notes on Gilding. When gilding single small articles, it is a good plan to hold the anode by its conducting wire in the left hand, so as to be able to control the amount of surface to be immersed in the bath, which must be considerably less (with hot solutions especially) than that of the article to be gilt. The object being slung by thin copper wire, the free end of the wire is to be twisted round the negative electrode (the wire issuing from the zinc of the battery), and the article then dipped into the bath. The article should gradually become coated, that is, in a few seconds, but not immediately after it is immersed. Gentle motion will secure an uniform deposit. After the article has become gilt all over, the anode may be lowered a little deeper into the bath, and the gentle motion of the article kept up for a short time, say from three to five minutes, or until it appears to be fairly coated. The length of time the article is to remain in the bath must be regulated by the price to be paid for the gilding. If a really good gilding is required, it may be necessary, after about five minutes' immersion, to rescratch-brush the article, dip it in the mer- curial solution for a moment, or until it is white, and then, after well rinsing, give it a second coating. Ordinary gilding, however, is generally accomplished in a single immersion. 1, Gilding Jewellery Articles. Chains, brooches, rings, pins, and other small articles of silver or metal jewellery should first be slung upon thin copper wire, then dipped for a few moments only in a warm potash bath. The articles are then to be rinsed in warm water and scratch-brushed, after which they are again rinsed, and at once immersed in the gold bath. When sufficiently gilt, the work should be rinsed in a vessel kept specially for the first rinsing, which should be saved, and afterwards in clean water. It is then to be properly scratch -brushed, and plunged into hot water ; next shaken about to remove as much water as possible, and finally put into warm boxwood sawdust. After moving it about in the boxdust for a few moments, the article requires to be shaken or knocked against the palm of the hand, to dislodge the sawdust. It is now ready to be wrapped up for the customer, pink tissue paper being preferable for gilt work, and blue or white tissue paper for silver or plated work. 2. Treatment of Gilding Solutions.^- When the gilding bath has been KEEPING THE SOLUTIONS UNIFORM. 2OQ heated for a few hours, it will have lost a considerable proportion of its water, which must be made up by adding an equivalent of hot water. If this is not done, the bath, being stronger than it was originally, will probably yield a non- adhering deposit, and the gold may strip off the work under the scratch-brush. The solution should be kept up to its standard height in the gilding vessel by frequent additions of hot water during the whol time it is subjected to evapo- ration by the gas-burner, or other heating medium. The solution- line of the bath should be marked upon the inside of the vessel when the liquid is first poured in. 4. Gilding different Metals. Silver and metal articles should not be slung upon the same wire and immersed in the bath at the same time, since brass, gilding metal, and copper receive the deposit more readily than silver. The latter metal should first receive a coating, after which, if time is an object, the metal articles may be placed in the bath with the partly -gilt silver articles. 5. Employment of Impure Gold. When it is desired to make up a gold solution from impure material, as from " old gold," for instance, the alloy should first be treated as follows : To I ounce of the alloyed gold, if of good quality say 1 8 -carat gold, for example add 2 ounces of silver, which should not be below standard ; melt them in a crucible with a little borax, as a flux. When the alloy is thoroughly melted it is to be poured into a deep vessel containing cold water, which must be briskly stirred in one direction, while the molten alloy is being poured in. This operation, termed granulation, causes the metal to assume the form of small lumps, or grains, as they are called. The water is now to be poured off and the grains of alloy collected and placed in a flask, such as is shown in Fig. 70. To remove the silver and copper from the granulated metal, a mixture of two parts water and one part strong nitric acid is poured into the flask, which is then placed on a sand-bath, moderately heated, until the red fumes which at first appear have ceased to be visible in the bulb of the vessel. The clear liquid is now Fi &- 7 8 ' to be carefully poured off into a suitable vessel a glass "beaker," such as is shown in Fig. 78, being a convenient vessel for the purpose. A small quantity of the dilute acid should then be poured into the flask, and heat again applied, in order to remove any remaining copper or silver. If, on the addition of the fresh acid, red fumes do not appear in the flask the operation is com- plete, and the grains of metal will have assumed a dark brown colour. The acid must now be poured off, and the grains well washed, whilo in the flask, with distilled water. The residuum is pure gold and 2IO NOTES ON GILDING. may be at once dissolved in aqua regia, and treated in the same -way as recommended for ordinary grain gold. The silver may readily be recovered from the decanted liquor, which, owing to the presence of copper removed from the original alloy, will be of a green colour, by immersing in it a strip of stout sheet copper, which in the course of a few hours will reduce the silver to the metallic state, in the form of a grey, spongy mass. When all the silver is thus thrown down, the green liquor is to be poured off and the silver deposit well washed with hot water. Being now pure silver, it may be used for making up solution, or fused with dried carbonate of potash into a button. 6. Gilding Filigree Work. Silver filigree work which has been an- nealed and pickled assumes a dead-white surface, which does not readily " take " the gilding unless the bath is rich in gold and free cyanide, and the current strong. If such parts of the article as can be reached by the scratch-brush are brightened by this means, the interstices which have escaped the action of the brush will sometimes be troublesome to gild, while the brightened parts will readily receive the deposit. In this case, if the bath is wanting in free cyanide, an addition of this substance must be made, and the article must be kept rather briskly moved about in the solution, and a good surface of anode immersed until the dead-white portions of the article are gilt. The anode may then be raised a little, and the piece of work allowed to rest in the bath, without movement, until the desired colour and thickness of coating are obtained. Some persons prefer dipping this kind of work in the mercury solution before gilding, by which a more uniform deposit is obtained. This plan is useful when the gold bath has been recently prepared. It must not be forgotten, however, that in gilding filigree work the battery current must be brisk. 7. Gilding Insides of Vessels. It sometimes happens, when gilding the interior of silver or electro -plated tankards, mugs, &c., which have been highly embossed or chased, that the gold, while depositing freely upon the prominent parts, refuses to deposit in the hollows. To overcome this, and to render the deposit uniform, the solution should be well charged with free cyanide ; the current must be of high tension (a Bunsen, for example), and the anode should be kept in motion during the first few moments. In this way very little trouble will be experienced from the causes referred to. It is im- portant, however, that insides of such embossed work should be very thoroughly scratch-brushed in the first instance ; indeed, as a mecha- nical assistant, the scratch -brush lathe is the gilder's best friend. 8. Old Solutions. When a gold solution has been much used it acquires a dark colour, from being contaminated by impurities ae beer from the scratch -brush lathe, &c., and in this condition if likely to yield a deposit of a dull red-brown colour, which, MANAGEMENT OP GOLD BATHS. 211 while being favourable to certain classes of work which can be readily got at by the scratch -brush, is very objectionable to articles of jewellery which are required to present a clear orange -yellow colour in all parts, including the interstices and soldered joints which cannot be reached by the lathe -brush. When the solution is in this condition we have found it advantageous to evaporate it to dryness, then to re -dissolve it in hot distilled water, filter the solution when cold, and add a small proportion of free cyanide, finally making up the bath to about three - fourths of its original volume. The solution thus treated yields a very rich colour in gilding. It is necessary to mention, however, that gold solutions which have been prepared by precipitating the gold from its chloride with ammonia should not be evaporated to dryness, since the explosive fulminate of gold may be present to some extent, which would render the operation hazardous. 9. Management of Gold Baths. The colour of the gilding may b5 varied from a pale straw or lemon colour to a dark orange -red at the will of the operator ; thus, when the solution is cold, a pale lemon-coloured deposit will be obtained. If the bath be warm, a very small surface of anode exposed in the solution, and the article kept in brisk motion, the deposit will also be of a pale colour. If, on the other hand, there be a large excess of cyanide in the bath, a considerable surface of anode immersed and a strong current, the gilding will be of a dark red colour, approaching a brown tone, and the article, when scratch- brushed, will assume a rich orange -yellow colour, specially suited to certain classes of work, as theinsides of cream-ewers, goblets, &c., and chains of various kinds. In order to obtain uniform results in any desired shade, when gilding a large number of articles of the same class, care must be exercised to keep the temperature of the bath uniform ; the anode surface immersed in the solution the same for each batch of work, consisting of an equal number of pieces of the same dimensions ; the battery current as uniform as possible, and, lastly, fresh additions of warm distilled water must be added frequently to the bath to make up for loss by evaporation. If these points be observed there will be no trouble fa obtaining uniform results. It is scarcely necessary to state that a large bulk of gilding solution will keep in an uniform condition for a longer period than a smaller quantity, since the effect of evaporation is less marked than in the latter case. 10. Worn Anodes. It is not advisable to employ anodes which have become ragged at the edges for gilding the insides of vessels, since particles of the metal are liable to be dislodged during the gilding process, and, falling to the bottom of the vessel, protect those parts upon which they drop from receiving the deposit ; indeed, the smaller fragments will sometimes become electro-soldered to the bottom of the vessel, causing some trouble to remove them. When the edges of an 2T2 NOTES ON GILDING. anode are very ragged it is well to trim them with shears or a pair of sharp scissors before using the anode for gilding insides. The anode should always be formed into a cylinder, and not used as a flat plate for these purposes, otherwise the deposition will be irregular, and the hollow surfaces of chased or embossed work may not receive the deposit at all. 1 1 . Defects in Gilding. When the gold becomes partially dissolved off portions of an article while in the gilding-bath, it generally indicates that there is too great an excess of cyanide in the solution. The same defect, however, may be caused by the current being too weak, the liquid poor in gold, too small a surface of anode in the solution, or by keeping the articles too briskly in motion in a bath containing a large excess of cyanide. Before attempting an alteration of the solu- tion, the battery should be looked to, and, if necessary, its exciting liquids renewed. The solution should then be well stirred and tried again ; if the same defect is observed an addition of chloride of gold should be made to the bath to overcome the excess of cyanide. If the deposit is of a very dark red colour, and of a dull appearance, this may be caused by employing too strong a current, by excess of cyanide, or too great a quantity of gold in the bath. If from the latter causes, the solution must be diluted ; if from the former, the articles should be suspended by a very thin slinging wire, or the positive element of the battery partially raised out of the battery-cell. 12. Gilding Pewter Solder. Common jewellery is frequently repaired with pewter solder, which does not so readily take the gilding as the other parts. A good plan to overcome this is first to well scratch - brush the articles, after which the solder may be treated as follows : Make a weak acid solution of sulphate of copper, dip a camel-hair brush into the solution and apply it to the soldered joint, and at the same time touch the spot with a steel point ; in a few seconds the solder will become coated with a bright deposit of copper. Now rinse the article, and proceed to the gilding as usual, when it will be found that the soldered part upon which the film of copper has been deposited will readily receive a coating of gold, more readily, in fact, than the body of the article itself. The article, when gilt, is then scratch- brushed and treated as usual. The copper solution for the above purpose may be prepared by dissolving about ^ oz. of sulphate of copper in ^ pint of water, and adding to the solution about J oz. of oil of vitriol. 13. Gilding Cheap Jewellery. This class of work, whether of French or Birmingham manufacture, seldom requires more than a mere dip to meet the requirements of the customer ; indeed, the prices obtainable for gilding articles of this character will not admit of gilding in the proper sense of the term. In France it is usual to employ a platinum STRIPPING GOLD FROM SILVER. 213 anode, and to renew the gilding solution as it becomes exhausted of its metal by fresh additions of gold salt. The author has found it a very economical plan to use a copper anode for gilding work of this description, and by making small additions of chloride of gold when the bath exhibited signs of weakness, he has been able to gild a very large number of articles, of a very fine colour, with an infinitesimal amount of the precious metal. The only preparation such work received was a good scratch-brushing before gilding, and a very slight scratch -brushing after. In his experience, although the prices were very low, the result was exceedingly profitable. Against the employment of a copper anode, it has been argued that the solution must of necessity become highly impregnated with copper. To which we may reply that we did not find such to be the case in practice. 14. Gilding German Silver. Since this alloy of copper, &c., will gene- rally receive a coating of gold in ordinary cyanide solution, without the aid of the battery, the solution should be somewhat weaker, and the battery current also, otherwise the gold will not firmly adhere. The temperature of the solution should also be lower than is required for gilding articles of silver or electro -plate. When German silver articles are first placed in the gilding -bath a small surface of anode only should be immersed, and the deposit allowed to take place gradually. If these precautions be not observed the operator may suffer the annoyance of finding the work strip when the scratch-brush is applied, or at all events under the operation of burnishing. 15. Stripping Gold from Silver. This may be done by making the article the anode in a strong solution of cyanide of potassium, or in an old gold solution containing a moderate amount of free cyanide. A quicker process, however, consists in immersing the articles in strong nitric acid, to which a little dry common salt is added. Care must be taken not to allow the article to remain in the stripping solution one moment after the gold has been removed, and the articles should be moved about in the liquid, especially towards the close of the opera- tion, to facilitate the solution of the gold from the surface. The gold may afterwards be recovered from the exhausted acid bath by im- mersing in it several stout pieces of sheet zinc or iron, which will precipitate the gold in the metallic state, and this may be collected, dried, and fused with a little dried carbonate of potash. Or the exhausted stripping solution may be evaporated to dryness, and the residuum fused with dried carbonate of potash or soda, a little nitre being added towards the end of the operation, to refine it more completely. 16. Spurious Gold ' 'Mystery Gold. ' ' Many attempts have been made from time to time to form an alloy which, having somewhat the colour 214 NOTES ON GILDING. of gold, would also withstand the action of the usual test for gold nitric acid. The introduction of the electro -gilding art greatly favoured such unscrupulous persons as desired to prey upon the public by selling as gold electro -gilt articles, which had not a fraction of the precious metal in their composition. An alloy of this kind entered the market many years ago, in the form of watch-chains and other articles of jewellery, the composition of which was, copper 16 parts, platinum 7 parts, and zinc I part. This alloy, when carefully prepared, bears a close resemblance to i6-carat gold, and when electro-gilt would readily pass for the genuine article. The manufacture of this variety of spurious gold seems to have received a check for a certain period ; but somewhat recently, in a modified formula, it has reappeared, not only in the form of articles of jewellery, but actually as current coin, and from its highly deceptive character, being able to resist the usual test, it has acquired the name of " Mystery Gold." It appears that, when converted into jewellery, the chief aim of the " manufacturers " is to defraud pawnbrokers, to whom the articles are offered in pledge ; and, since they readily withstand the nitric acid test, the "transac- tions " are often successful. According to Mr. "W". F. Love, in a communication to the Chemical News, a bracelet made from an alloy of this character had been sold to a gentleman in Liverpool, and when the gilding was removed the alloy presented the colour of 9-carat gold. The qualitative analysis proved it to be composed of platinum, copper, and a little silver. A quantitative analysis yielded the following result : Silver V 2 '4 8 Platinum ; . 32*02 Copper (by difference) . . . . . . 65*50 It was found that strong boiling nitric acid had apparently no effect upon it, even when kept in the acid for some time. 17. Gilding Watch Dials. To prepare a silver watch dial (for ex- ample) for gilding, it should be laid, face upward, upon a flat piece of cork, and the face then gently rubbed all over with powdered pumice, sifted through a piece of fine muslin, and slightly moistened with water, using the end of the third finger of the right hand for the purpose. The finger being dipped in the pumice paste, should be worked with a rotary motion over the surface of the dial, so as to pro- duce a perfectly uniform and soft dulness. When this is done, a piece of copper slinging wire is passed through the centre hole of the dial, and formed into a loop ; the dial is then to be rinsed, and placed in the bath, care being taken not to touch the face of the article either before or after gilding, except in the way indicated. The dial must afterwards be repainted. SLINGING WIRES. 215 1 8. Gilding solutions which have been worked with but a small excess of cyanide are apt to deposit more gold than is dissolved from the anode, by which the action of the bath becomes lessened, while the colour of the gilding is indifferent. It must always be borne in mind that in all cyanide solutions, but more especially such as are worked hot, the cyanide of potassium gradually becomes converted into car- bonate of potassium by the action of the atmosphere, and therefore loses its solvent power. 19. For producing a dead or matted surface upon brass articles of jewellery, as brooches, lockets, &c., they are first dipped for an instant in a mixture composed of equal parts of sulphuric and nitric acids, to which a small quantity of common salt is added, and imme- diately plunged into cold water. After being rinsed in one or two other waters, they are promptly immersed in the gilding-bath, in which, after a moment's immersion, they acquire the desired colour of gold. After rinsing in hot water, they are finally dried in hot box- wood sawdust. In treating this class of work, care should be taken to avoid handling the pieces ; after they have been removed from the sawdust they should be at once wrapped up ready for delivery. 20. When it is desired to give a stout coating of gold to an article, it should be occasionally removed from the gilding-bath, then scratch- brushed, rinsed, and returned to the bath. If the article were allowed to remain in the bath undisturbed until a thick coating was deposited, the surface would probably be rough and crystalline, and moreover liable to strip when being scratch-brushed. It is sometimes the prac- tice to dip the article for an instant in the quicking solution after each gilding, by which the respective layers of gold are less apt to separate in scratch -brushing or burnishing. 21. The wires used for slinging articles in the gilding-bath should never be reversed, but one end only employed for suspending the articles, the other being used for connection with the negative elec- trode of the battery. By adopting this system, the gold deposited upon the ends of the slinging wires is less liable to become wasted than when both ends of the wires are used indiscriminately. After the slinging wires have been used a few times, and before the gold upon them begins to chip or peel off, they should be carefully laid aside, with all the gilt ends in one direction, so that the gold may be removed, by stripping, at any convenient time. After stripping off the gold, the wires should be annealed, then pulled out straight, and placed in bundles. Before being again used, each end of the bundle of wires should be dipped for a few moments in an old dipping-bath, and then rinsed, when they will be ready for future use. It is better to treat slinging -wires thus carefully than to suffer them which is commonly the case to be scattered about. 2l6 NOTES ON GILDING. 22. Gilding Lead, Britannia Metal, $c. When articles composed of lead, tin, Britannia metal, iron, or steel are required to be gilt, it is best to give them a preliminary coating of copper in an alkaline bath, or to electro-brass them, after which they may be gilt with perfect ease, and with but little liability to strip when scratch -brushed. The softer metals, however, will require to be burnished with great care, owing to their yielding nature under the pressure of the burnishing tools. The same observation also applies, inversely, to silvered or gilt steel work, in which case the superior metals, being softer than steel, become expanded under the influence of the burnishing tools, and are consequently liable to become separated, in blisters, from the underlying harder metal. 23. Excess of Cyanide Injurious. When a newly prepared gilding solution is first used (hot), the deposit is usually of a rich, fine gold colour, if a sufficient quantity of free cyanide has been employed in its preparation, a proper surface of anode immersed in the solution, and the current brisk. If, on the other hand, the colour is pale that is yellow, without the characteristic orange tint this indicates that one or other of the above conditions is wanting. Before venturing to increase the amount of free cyanide, the condition of the battery should be examined, the temperature of the solution raised a little, and a larger anode surface immersed, when, if the solution still yields a light-coloured deposit, an addition of strong cyanide solution must be given gradually until the gilding assumes the proper orange-yellow colour. The addition of cyanide must always be made with caution, for if too great an excess be applied, the solution is apt to yield brown deposits, quite unsuitable for many articles of jewellery ware. This quality of gilding, however, is frequently taken advantage of for articles which are required lo have a deep gold colour after scratch -brushing, as the insides of tankards, &c., and also Albert chains and work of a similar description. If a gold solution is in really good working condition, and the current sufficiently brisk, a copper or brass article should gild readily, in hot solutions, with an anode surface considerably less than that of the cathode, or article being gilt, especially if no motion be given to either electrode. A silver article, however, would require, in the same bath, a much larger surface of anode, but more especially if the surface were frosted, as in filigree work. In gilding articles of this description it is better to expose a large anode surface and keep the article in gentle motion when first put into the bath, after which a portion of the anode may be withdrawn, and the object allowed to rest undisturbed until the coating is sufficiently thick. 24. In working small baths, additions of hot distilled water must be given frequently to make up for the loss by evaporation ; but where DISCOLOUEED SOLUTIONS. 21 7 large quantities of solution are employed, this addition need not be made more than once a day, or at the close of the operation. "With this exception, a good gilding solution will continue to give uniformly good results for many days especially if large in bulk without alteration. "When it begins to work tardily, however, which may readily be seen by the extra anode surface required to gild the articles promptly, moderate addition's of cyanide must be given until the bath acquires its normal activity. 25. After working gilding -baths for a lengthened period, they generally assume a brown colour, and the gilding is, under such circumstances, of an indifferent colour. The chief causes of this dis- coloration have been already explained, and can be to a great extent avoided, by thoroughly rinsing the articles before putting them in the bath. When a solution is in this condition the best remedy is to evaporate it as before, and then redissolve the dried mass in distilled water, using about one -third less water than the original bulk. A little fresh cyanide must also be added, and the solution filtered, after which it will generally yield a deposit of excellent colour. Old solu- tions which give deposits of a greenish -black colour may be improved by evaporation, but the heating of the dried product should be carried somewhat farther than in the former cases. It is better, however, to abandon such a solution altogether and to make a fresh one. The gold from the waste solution may afterwards be recovered by the processes given in another chapter. When gilding solutions, after being worked some time, yield a pale straw-coloured gilding, this is attributed by some to the gradual accumulation of silver from the gold anodes (which always contain a trace of silver) ; we are, however, disinclined to accept this view, owing to the exceedingly small quantity of silver present in fine gold ; moreover, since silver deposits first, if present in a gold solution, we doubt its liability to accumulate in the bath. We would rather attribute the paleness of deposit referred to, to one or both of the following causes : I . To the presence of a large excess of carbonate of potash in the bath from using an inferior cyanide ; 2. To the presence of tin derived from pewter soldered articles, imper- fectly prepared for gilding. 26. The Bunsen battery is most generally used for gilding, and indeed the current from this source produces a gold deposit of very fine colour. It must be used with caution, however, when gilding articles at a low price, since it deposits the metal very freely from hot solutions, and would soon yield a coating of gold of greater thickness than would pay for ordinary cheap work. In gilding with this battery, the regulation of the anode surface in solution should be strictly observed, only a sufficient surface being exposed to enable the article to become gilt almost immediately after immersion ; the anode 2l8 NOTES ON GILDING may be gradually lowered a little as the deposition progresses. Articles that only require to receive a mere colour of gold upon them (as in cheap jewellery) should be first scratch -brushed, then well rinsed in hot water ; dipped for a moment in the gold bath, then rinsed, and lightly scratch -brushed again, and after again rinsing receive a momentary dip in the gilding bath ; they are to be finally rinsed in boiling water, then shaken well, and placed in hot boxwood sawdust, from which they are afterwards removed and well shaken to cleanse them from this material. CHAPTER XVII. ELECTRO -DEPOSITION OJF SILVER. Preparation of Nitrate of Silver. Observations on Commercial Cyanide. Preparation of Silver Solutions. Bright Plating. Deposition by Simple Immersion. Whitening Articles by Simple Immers on. Whitening Brass Clock Dials, &c. THE process of " electro -plating " may be considered tlie most impor- tant branch of the great art of electro-deposition. Not only is it invaluable in giving to articles manufactured from German silver, Britannia metal, and other metallic surfaces, a beautifully white coating of the precious metal even superior in brilliancy to that of standard silver, but old plated and electro -silvered articles, from which the silver has worn off, may be resilvered by this process and made to look nearly equal to new, which there was no practical means of doing before the introduction of electro -plating. This term, by-the- bye, though generally used, is erroneous, since the process of plating consists in attaching two plates, or ingots of metal, and rolling them into sheets, from which, as in the old manufacture of Sheffield plate, various articles of utility are, or rather were, made. Preparation of Nitrate of Silver. Since the silvering or " plat- ing " solutions with one exception are prepared from the nitrate of silver, it will be necessary to consider its preparation previous to explaining the various ways in which silver baths are made up from this salt of silver. To prepare nitrate of silver, the required quantity of grain silver is carefully put into a glass flask * or evaporating dish, the former by preference, since during the chemical action which ensues while the solution of the metal is taking place, a portion of the metal may be lost by the spitting of the solution when the chemical action is at its height. In dissolving silver, take, say Grain silver 2 ounces. Pure nitric acid 3i Distilled or rain water . . . . . ij * When dissolving large quantities of siiver, a stoneware vessel may be employed. 220 ELECTRO-DEPOSITION OF SILVER. Put the silver carefully into the flask, then add the water, and lastly the acid. In a few moments vigorous ebullition takes place, with the disengagement of red fumes of nitrous gas, which should be allowed to escape through the chimney. When the action begins to quiet down a little, the flask must be placed on a warm sand-bath. For small operations, or where a proper sand-bath is not provided, an ordinary frying-pan nearly half -filled with silver- sand will answer the purpose well. The flask should remain upon the sand-bath until the red fumes cease to appear in the bulb, at which period the chemical action is at an end. It may be well to mention that, in dissolving silver, it is advisable in the first instance to use rather less of the acid than is necessary to dissolve the whole of the silver, and to treat the undissolved portion separately, by which means excess of acid is avoided. The nitrate of silver solution must now be decanted into an evaporating dish and placed in the sand-bath, where it is allowed to remain until a film or pellicle forms on the surface of the liquor, when the vessel must be set aside to cool. A few hours after, crystals of nitrate of silver will have deposited, from which the remaining liquor is to be poured off, and this again evaporated as before. Instead of crystallising the nitrate, it may simply be evaporated to nearly dry- ness, by which the free acid will become expelled. Should the nitric acid used in dissolving silver contain even a slight portion of hydrochloric acid, an insoluble white precipitate will be found at the bottom of the flask, which is chloride of silver. This, however, will not be injurious to the plating solution. Sometimes, also, a slight deposit of a brownish -black colour is found at the bottom of the vessel in which silver is dissolved ; this is gold, left in the gram silver through imperfect parting in the refining process. We have occasionally discovered more than a mere trace of gold at the bottom of the dissolving flask ; indeed in several instances an appre- ciable quantity. When dissolving the crystals of nitrate of silver, for the preparation of either of the following plating solutions, distilled or rain water only should be used, since river water always contains traces of sub- stances which form a white precipitate in the presence of nitrate of silver. In describing the silver solutions, the proportion of silver in the metallic state will be given, and it will be understood that in each case the weighed metal must be first converted into nitrate. We may also state that the proportion of silver to each gallon of solution may be varied according to the practice of the plater, some persons preferring solutions in which there is a moderate percentage of the metal, while others employ much greater quantities. The proportion of silver per gallon of solution ranges from | an ounce to 5 or 6 ounces, and even COMMERCIAL CYANIDE OF POTASSIUM. 221 more ; but for most practical purposes from i^ to 2 ounces will be quite sufficient ; indeed, some of our best results have been obtained with I ounce of silver per gallon. In most of the formulae given, I gallon of solution will be taken as the basis for making up any required quantity of silvering bath ; and it will be readily understood that when larger proportions of silver to the gallon are preferred, a proportionate increase of cyanide must be used, not only to dissolve the precipitated metal, but also to play the part of free cyanide in the solution. It must be remarked here, that unless the silvering-bath contains an excess of cyanide of potassium, the anode, or dissolving plate, whose function it is to resupply the solution with silver in the proportion in which it is deposited upon the articles, will not keep up the metallic strength of the bath, and consequently it will deposit the metal slowly. A large excess of cyanide, on the other hand, is not only unnecessary, but is liable to cause the deposited silver to blister and strip, or peel off the work under the pressure of the burnishing tools ; and when very greatly in excess, the coating will be so non- adherent that it may even yield to the scratch -brush, and separate from the underlying metal. Observations on Commercial Cyanide of Potassium. Since the cyanide of potassium is one of the most important and useful sub- stances that come under the command of the electro -depositor, while the success of his operations greatly depends upon its active quality, it is advisable to state that ordinary commercial cyanide varies considerably in this property ; so much so, indeed, as to render it absolutely neces- sary that the user should be put on his guard, lest in purchasing a cheap and worthless article, he should commit an error which may cost him much trouble and annoyance, as also pecuniary loss. Before making up any solution in large quantity, in which cyanide of potas- sium is the solvent, we advise him first to obtain samples of the com- mercial article, and to test them by either of the processes given in another chapter. We may state that some of the cheap cyanides con- tain a large excess of carbonate of potash. This substance, while being a necessary ingredient in the manufacture, is also frequently used greatly in excess to produce a cheap article, and may be called its natural adulterant. This salt (carbonate of potash), however, unless specifically recommended in the preparation of certain depositing solutions, is not only useless, but when greatly in excess reduces the conductivity of both silvering and gilding baths. Preparation of Silver Solutions. Solution I. The solutions of silver most generally used for electro -plating are those commonly called " cyanide solutions," the foremost of which is the double cyanide of silver and potassium, which is prepared as follows : I ounce of silver is converted into nitrate, as previously described, and the crystals rH- 222 ELECTRO-DEPOSITION OF SILVER. solved, with stirring, in about 2 quarts of distilled or rain water, which may, in the case of small quantities, be effected in a glass vessel or glazed earthenware pan. For large quantities a stoneware vessel should be used. When the crystals are all dissolved, a strong solution of cyanide (about ^ a pound, dissolved in I quart of water) is added, a little at a time, when a precipitate of cyanide of silver will be formed, which will increase in bulk upon each addition of the cyanide. Each time, after adding the cyanide solution, the mixture must be well stirred with a glass rod or strip of wood free from resin. When it is found that the addition of cyanide produces but little effect, it must be added very cautiously, since an excess will redissolve the precipitate, and cause waste in the after process of washing this deposit. To avoid adding too much cyanide, the precipitate should be allowed to fall down an inch or so, when a glass rod may be dipped in the cyanide solution, and the clear liquor touched with this, when if a milkiness is produced, a little more cyanide must be added, and the stirring resumed. After a short repose, the same test may be applied, and so on, until a drop of cyanide solution produces no effect. Great care must be taken not to add more cyanide than is absolutely necessary to throw down the silver. As an additional precaution, when nearly the whole of the silver is precipitated, the vessel may be allowed to rest for an hour or so, and the clear liquor then poured off and treated separately, by which means the bulk of the precipitate will be saved from the risk of coming in contact with an excess of cyanide. If, through accident or faulty manipulation, too much cyanide has been added, more nitrate of silver solution must be poured in, which, com- bining with the surplus cyanide, will again produce the characteristic milkiness ; and if the additions of nitrate are made with care, the clear liquor will be perfectly free from silver, and after allowing the cyanide of silver to deposit, may be poured off an 1 thrown away. Washing the Precipitate. In all such cases the precipitate should be allowed fully to settle; the supernatant liquor, or "mother liquor," is next to be poured off slowly, so as not to disturb the solid matter (cyanide of silver) ; a large quantity of fresh water which for this purpose may be common drinking water is now to be poured on to the precipitate with brisk stirring, and the vessel again left to rest, after which the clear liquor is to be poured off as before, these washings being repeated three or four times. Dissolving the Precipitate. To convert the cyanide of silver into the double cyanide of silver and potassium, the strong solution of cyanide must be added in moderate portions at a time, constantly stirring as before, until the precipitate appears nearly all dissolved, at which period the additions of cyanide must be made with more caution. In this case, as in the former, it is a good plan, when nearly the whole PREPARATION OF SILVER SOLUTIONS. 223 of the precipitate is dissolved, to allow the vessel to stand for a short time, then to pour off the clear liquor which is now a solution of the double cyanide of silver and potassium and to treat the remainder of the precipitate with cyanide solution ; by this means too great an excess of the solvent is avoided. When all the precipitated silver is redissolved, add about one-fourth more cyanide solution than that originally used, and pass the solution through a filter into the plating vat or depositing vessel, which may be conveniently done by means of a piece of unbleached calico (previously washed in lukewarm water to remove the " dressing") stretched over three strips of wood bound together in the form of Fig. 79. a triangle either with copper wire or string, as in Fig. 79. When all the solution has passed through the filter, this may be washed by pouring a little water over it while resting over the bath. The solution is finally to be made up to the full quan- tity by adding the necessary proportion of water, when its preparation is complete ; it will be better, however, to allow it to rest for twenty- four hours before using it for electro -plating. Free Cyanide. This term is applied, as we have before hinted, to a moderate excess of cyanide of potassium which it is always necessary to have in the bath, to dissolve the insoluble cyanide of silver which forms on the anode, but since the ordinary commercial article is of very variable quality, the addition of this substance must to a great extent depend upon the judgment of the plater, subject to the precau- tions we have previously given ; from one-fourth to one-half the quan- tity of cyanide used in dissolving the precipitate of cyanide of silver may be added to the solution as free cyanide, and water then added to make up i gallon. If the cyanide, in the first instance, be dissolved in a definite measured quantity of water, say at the rate of half a pound to a quart of water (40 ounces), the proportion of cyanide used in each of the former cases can be readily ascertained by simply measuring the balance of the solution and deducting its proportion of cyanide from the original weight taken. A fair quality of ordinary commercial cyanide should not contain less than 50 per cent, of pure cyanide, but we have frequently met with an article which contains a very much lower percentage, which should never be used for making up plating solutions, but may be employed in the less important process of dipping in the preparation of work for nickel-plating. Of course it will be understood that when cyanide containing a high percentage of the pure substance is obtained, a proportionately smaller quantity must be used. Solution II. One ounce or more of silver is converted into nitrate as before, and the crystals dissolved in from three to four pints of dis- 224 ELECTRO-DEPOSITION OF SILVER. tilled water. A solution of carbonate of potash (salt of tartar), con- sisting of about six or eight ounces of the salt to a pint of water, is to be gradually added to the solution of nitrate of silver, with constant stirring, until no further precipitation takes place. After settling, the clear liquor is poured off, and the precipitate (carbonate of silver) washed with water several times, as before directed. A strong solu- tion of cyanide is then to be added until all the precipitate is thoroughly dissolved, when a moderate excess is to be added as free cyanide. The solution should now be filtered and water added to make up one gallon, or such quantity in the same proportion of materials as may be required. In adding excess of cyanide to this and other solutions, it is always preferable to add it moderately at first, otherwise the work is very liable to strip. After working the bath for some time, an addition of cyanide may be made, but so long as the anode keeps perfectly clean while the work is being plated, the less free cyanide there is in the bath the better. A solution which has been worked for a considerable time acquires a good deal of organic matter, becom- ing dark in colour in consequence, and is then capable of bearing, without injury to the work, a larger proportion of free cyanide than newly prepared solutions. Solution III. Mr. Alexander Parkes, in 1871, patented a solution for depositing solid articles. One ounce of silver is first converted into nitrate, from which the silver is thrown down in the form of oxide of silver, by means of a solution of caustic potash gradually added, until no further precipitation takes place. After washing the oxide, it is dissolved in 2 gallons of water containing 16 ounces of cyanide of potassium. Solution IV. The best solution for depositing silver upon G-erman silver without recourse to the process of " quicking," is one which the author employed upon an extensive scale for many years with great success ; it is composed as follows, and although it is rather more expensive in its preparation than many other solutions, it is, so far as he is aware, the best solution in which German silver work may be plated without being previously coated with mercury, as in the " quicking " process hereafter referred to. To prepare the solution, I ounce of silver is converted into nitrate and dissolved in two or three pints of distilled water as before. About three ounces of iodide of potassium are next to be dissolved in about half a pint of distilled water. The iodide solution is to be gradually added to the nitrate solution, the operation being performed in a dark corner of the room, or preferably by feeble gaslight, when a bright lemon yellow precipitate will be formed. The liquid must be briskly stirred upon each addition of the iodide, and care must be taken not to add the latter salt on any account in excess, otherwise it will PREPARATION OF SILVER SOLUTIONS. 225 redissolve the precipitate. When the precipitation is nearly com- plete, it is better to allow the vessel to rest, and to put a little of the clear liquor in a test tube, Fig. 80, and to add a drop or two of the iodide solution, when if a cloudiness is produced, a moderate quantity of the iodide is to be added to the bulk and well stirred in. The clear liquor should be repeatedly tested in this way, until a single drop of the iodide solution produces no further effect upon it. In case of an accidental addition of too much iodide, nitrate of silver solution must be added to neutralise it. When the precipitation is complete, the vessel must be set aside in a dark place, since the iodide of silver is affected by light for an hour or so, after which the clear liquor must be poured off, and the precipitate repeatedly FigTso. washed with cold water. Lastly, the iodide of silver is to be dissolved in a solution of cyanide of potassium, and a moderate excess added as before recommended. In working this solution, whenever the anode becomes coated with a greenish film, an addition of cyanide must be made to the bath. Since the system of working the above solution differs in several respects from that adopted with other solutions, it may be well to describe our own practice in the treatment of German silver work. The articles are first placed in a warm solution of caustic potash, to remove greasy matter, after which they are well rinsed. Each article is then well scoured all over with powdered pumice and water, or finely powdered bath brick an excellent substitute for the former and water. As each article is brushed, it is to be well rinsed in clean water, and is then ready for the plating bath, in which it should be suspended without delay. Solution V. Mr. Tuck obtained a patent, in 1842, for " improve- ments in depositing silver upon German silver," in which he recom- mends, for plating inferior qualities of German silver, a liquid com- posed of sulphate of silver dissolved in a solution of carbonate of ammonia. Sulphate of silver is formed by adding a solution of sulphate of soda (Glauber's salt) to a solution of nitrate of silver, or by boiling silver with its weight of sulphuric acid. For plating the better qualities of German silver, cyanide of silver is dissolved in a solution of carbonate of ammonia. The proportions used are : Sulphate of silver 156 parts. Carbonate of ammonia (diss ed in distilled water) . 70 Or, Cyanide of silver . ' i y .... 134 Carbonate of ammonia . ...*.. ^t . . . . 70 226 ELECTRO-DEPOSITION OP SILVER. The silver salt in each case is boiled with the solution of the car- bonate of ammonia until it is dissolved. For coating common German silver, he adds half an ounce of sulphate of silver to a solution con- taining 107 grains of bicarbonate of ammonia. Solution VI. For producing very white deposits of silver, the following may be used : One ounce of silver is dissolved and treated as before, and the crystals of nitrate redissolved in about half a gallon of distilled water. A moderately strong solution of common salt is then prepared, and this is gradually added to the former, when a copious white precipitate of chloride of silver is formed, which must be well washed with cold water. After pouring off the last wash water, a strong solution of cyanide is to be added to the precipitate until it is all dissolved, when a moderate excess is to be added, and the solution carefully filtered through filtering paper, the first runnings to be passed at least twice through the same filter. Lastly, add water to make up I gallon. The solution may be used immediately, but will work better after a few hours' rest. This solution is very useful for obtaining delicately white deposits, but is not suitable for ordinary plating purposes, since the deposited silver is liable to strip under the action of the burnisher. If used somewhat weaker than in the above proportions, with a moderate current and small anode surface, the deposit will adhere to most metals with tolerable firmness ; it is, how- ever, most suitable for coating articles which are either to be merely scratch-brushed or left a dead white. Chased figures and cast metal work receive a brilliant white coating in this solution, but to retain their beauty they must be kept beneath a glass case, since the fine silver surface soon discolours in the atmosphere. Solution VII. This plating solution, which is one of the best for most; purposes, is prepared by dissolving silver in a solution of cyanide, by aid of the electric cur- rent. Suppose we wish the solution to contain I ounce of silver per gallon. The required quantity of water is first put into the bath, and for each gallon of liquid about 3 ounces of good cyanide is added, and allowed to dissolve. Fig. 81. A porous cell is now to be nearly filled with this solution, and stood upright in the vessel containing the bulk of cyanide solution, the liquid being at the same height in both vessels. A strip of sheet copper is next to be connected to the negativ* 4 PKEPAKATION OF SILVER SOLUTIONS. 227 electrode of a strong voltaic battery, and placed in the porous cell. A large sheet of silver is next to be connected to the positive elec- trode, and immersed in the larger vessel. The arrangement is shown in Fig. 81. The weight of the sheet silver being ascertained before- hand, the battery is allowed to remain in action for several hours, when the silver plate may be weighed to determine how much of it has been dissolved in the solution, and the action is to be kept up until the proper proportion has been dissolved by the cyanide in the outer vessel. When this point has been reached the porous cell is to be removed, and its contents may be thrown away. Another electrolytic method of preparing a silver bath is the follow- ing : To make a bath containing, say, one ounce of silver per gallon, the cyanide should be of known strength. Assuming the commercial article to contain 50 per cent, of real cyanide, about 3 ounces are to be dissolved in each gallon of water ; a large silver anode connected to the positive pole of a battery is to be suspended in the solution, and a smaller plate of silver as a cathode. A strong current should be used, and the anode weighed from time to time until the desired proportion of silver has become dissolved into the solution. The con- dition of the bath may then be tested by suspending a clean plate of brass from the negative rod, at the same time immersing about an equal surface of anode, using a moderate current, when if the solu- tion be in good working order, the cathode will at once receive a bright deposit of silver. During the action some caustic potassa is formed in the liquid, which may be converted into cyanide, by adding a moderate quantity of hydrocyanic acid, which must be done, however, with exceeding care, owing to the deadly nature of the acid, the vapour of which must not on any account be inhaled. Respecting the use of this acid, however, we must strongly recommend that its em- ployment should never, under any circumstances whatever, be placed in the hands of persons unacquainted with its highly poisonous character. Besides the foregoing, many other processes for preparing silver solutions have been proposed ; but since they are comparatively of little or no practical value, they deserve but a passing reference. By one of these processes chloride of silver is dissolved in hyposulphite of soda. The salt of silver thus formed (hyposulphite of silver) is readily acted upon by light, and the silver, being thus converted into an insoluble sulphide, gradually becomes deposited at the bottom of the bath. Solutions have also been prepared by employing ferrocyanide of potassium (yellow prussiate of potash) as the solvent of cyanide of silver. Again, the silver has been precipitated from its nitrate solu- tion by lime-water, forming oxide of silver ; as also by ammonia, soda, magnesia, &c. ; the various precipitates being subsequently dis- solved in a solution of cyanide of potassium. The ordinary double 228 ELECTRO-DEPOSITION OF SILVER. cyanide of silver and potassium solution, however, will be found most useful for the general purposes of electro-plating. Bright Plating. The silver deposited from ordinary cyanide solu- tions is of a pearly white or dull white, according to the condition and nature of the silver solution, and the strength of the current ; and it is necessary to brighten the work by scratch -brushing before it is subjected to the operations of burnishing or polishing. It is possible, however, by adding to the plating-bath a small quantity of bisulphide of carbon, to obtain deposits of silver which are bright instead of dull, for the discovery of which important improvement we are indebted to Mr. W. Milward, of Birmingham, who made the discovery in the fol- lowing way : He had observed that when wax moulds for electro - typing, which had been coated with a film of phosphorus by applying a solution of that substance in bisulphide of carbon, were put into the cyanide plating solution to receive a deposit of silver, that other articles as spoons and forks, for example silvered in the same solu- tion, assumed a brightness more or less uniform, sometimes extending all over the articles, and at others occurring in streaks and patches. This led him to try the effect of adding bisulphide of carbon alone to the platmg solution, which produced very satisfactory results. The improvement was worked as a secret for some time, but eventually leaked out, in consequence of which Mr. Milward and a person named Lyons (who had become acquainted with the secret) took out a patent in March, 1847, for bright silver deposition by adding "compounds of sulphur and carbon," bisulphide of carbon being preferred. From that time the bisulphide of carbon has been constantly employed for producing bright deposits of silver. To make up the solution for " bright plating," the following methods are adopted: i. " 6 ounces of bisulphide of carbon are put into a stoppered bottle, and I gallon of the usual plating solution added to it ; the mixture is first to be well shaken, and then set aside for 24 hours. 2 ounces of the resulting solution are then added to every 20 gallons of ordinary plating solution in the vat, and the whole stirred together ; this proportion must be added every day, on account of the loss by evaporation, but where the mixture has been made several days, less than this may be used at a time. This proportion gives a bright deposit, but by adding a larger amount a dead surface may be obtained, very different to the ordinary dead surface." Another method of preparing a solution for bright plating is the following : Put 1 quart of ordinary silver plating solution into a large stoppered bottle ; now add 1 pint of strong solution of cyanide and shake well ; 4 ounces of bisulphide of carbon are then to be added, as also 2 or 3 ounces of liquid ammonia, and the bottle again well shaken, which operation must be repeated every two or three hours. BRIGHT PLATING. 2 29 The solution is then set aside to rest for about 24 hours, when it will be ready for use. About 2 ounces of the clear liquid may be added to every 20 gallons of ordinary plating solution, and well mixed by stirring. A small quantity of the brightening solution, or ' ' bright, ' ' as it is termed in the plating-room, may be added to the solution every day, and the liquid then gently stirred. In course of time the bisulphide solution acquires a black colour, to modify which a quantity of strong cyanide solution, equal to the brightening liquor which has been removed from the bottle, should be added each time. In adding the bisulphide solution to the plating bath an excess must be avoided, otherwise the latter will be spoilt. Small doses repeated at intervals is the safer procedure, and less risky than the application of larger quantities, which may ruin the bath. A very simple way to prepare the brightening solution is to put from 2 to 3 ounces of bisulphide of carbon in an ordinary " Winches- ter " bottle, which holds rather more than half a gallon. Now add to this about 3 pints of old silver solution, and shake the bottle well for a minute or so ; lastly, nearly fill the bottle with a strong solution of cyanide, shake well as before, and set aside for at least 24 hours. Add about 2 ounces (not more) of the "bright" liquor, without shaking the bottle, to each 20 gallons of solution in the plating vat. Even at the risk of a little loss from evaporation, it is best to add the brightening liquor to the bath the last thing in the evening, when the solution should be well stirred so as to thoroughly diffuse the added liquor. The night's repose will leave the bath in good working order for the following morning. Other substances besides the bisulphide of carbon have been used, or rather recommended, for producing a bright deposit of silver, but up to the present no really successful substitute has been practically adopted. Amongst other compounds which have been suggested, are a solution of iodine and gutta-percha in chloroform, which is said to have a more permanent effect than the bisulphide ; carbonate, and acid carbonate of potassium, i| ounce of each, added once every nine or ten days to a plating solution containing 12 ounces of cyanide and 3^ ounces of silver per gallon. According to Plante, bright silver deposits may be obtained by adding a little sulphide of silver to the plating solution. Although the solution for "bright plating " is useful for some pur- poses, it is not adopted as a substitute for the ordinary cyanide of silver bath for the general purposes of electro -plating. For articles which have deep hollows and interstices which cannot be burnished without considerable difficulty, and for the insides of tea and coffee- pots, and articles of a similar description, which are required to be bright, but which cannot be rendered so by mechanical methods, a 230 ELECTRO-DEPOSITION OP SILVEE. slight coating of bright silver is an advantage. A bath of brightening solution is usually kept for this purpose, in which the articles, after being plated in the ordinary way, are immersed for a short time, by which they receive a superficial coating of the bright deposit. In the "bright solution" the articles first become bright at their lower surface, the effect gradually spreading upward, until in a short time they become bright all over, when they are removed from the bath and immediately immersed in boiling water, otherwise the silver would quickly assume a dark colour. Deposition by Simple Immersion. Articles of brass and copper readily become coated with a film of silver, without the aid of the battery current, in tolerably strong solutions of the double cyanide of silver and potassium ; the deposit, however, is not of such a degree of whiteness as to be of any practical use. Other solutions of silver are therefore employed when it is desired to give a slight coating of this metal to small brass or copper work which will present the necessary brilliant white colour. Silver may also be deposited upon these surfaces by means of a paste of chloride of silver, to which common salt or cream of tartar is added. The following processes are those most generally adopted : Whitening Articles by Simple Immersion. For small brass and copper articles, as buttons, hooks and eyes, coffin-nails, &c., silvering by simple immersion is employed ; and in order to produce the best possible effect, the solution bath should not only be prepared with care, but kept as free as possible from contamination by other substances. To prepare a bath for this purpose, a given quantity of fine grain silver is dissolved in nitric acid. The solution of nitrate of silver thus formed is added to a large quantity of water, a strong solution of common salt is then poured in, which precipitates chloride of silver in the form of a dense white precipitate. When the whole of the silver is thrown down (which may be ascertained by adding a drop or two of hydrochloric acid or solution of salt to the clear liquor) the precipitate is allowed to subside, after which the supernatant liquor is to be poured off, and the precipitate washed several times. The last rinsing water should be tested with litmus paper, when, if there be the least trace of acid, further washing must be given. The precipitate, which is very readily acted upon by sunlight, should be prepared in a dull light, or by gaslight, and, if not required for imme- diate use, it should be bottled and kept in a dark cupboard. The chloride of silver is to be mixed with at least an equal weight of bi- tartrate of potassa (cream of tartar), and only sufficient water added to form a pasty mass of the consistency of cream. In this mixture the articles, having been previously cleaned or dipped, are immersed, and stirred about until they are sufficiently white, when they are to WHITENING AETICLES BY SIMPLE IMMEESION. 231 be rinsed in hot water, and shaken up with boxwood sawdust. These preparations are also used for silvering clock-faces, thermometer and barometer scales, and other brass and copper articles, by being rubbed over the surface to be whitened with a cork. Another chloride of silver paste, for whitening articles of brass or copper, may be made by taking chloride of silver and prepared chalk, of each one part, common salt i part, and pearlash 3 parts, made into a paste, as before. A third mixture is prepared by taking chloride of silver I part, cream of tartar at least 80 parts, to which is sometimes added about 80 parts of common salt. The whole are dissolved in boiling water. This solution acquires a greenish tint, from the presence of copper, which takes the place of the silver in the liquid. In using tins solution the articles are introduced by means of a perforated basket, which is briskly stirred about in the hot liquid until uniformly white. Some operators modify the above solution by adding common salt, Glauber's salt, corrosive sublimate, caustic lime, &c., but it is doubtful whether any advantage is derived therefrom. A process, which is to be applied cold, was proposed by Roseleur, and seems to have worked exceedingly well in his experienced hands. A solution of the double sulphite of silver is formed in the following way : Four parts of soda crystals are dissolved in five parts of distilled water, sulphurous acid gas (prepared by heating in a glass retort strong oil of vitriol with some small pieces of copper wire) is then passed through the liquid, by allowing it to bubble through mercury at the bottom of the vessel, to prevent the exit tube from becoming clogged with crystals ; the gas is allowed to pass until the fluid re-dissolves the crystals of bicarbonate, and slightly reddens blue litmus paper. It is then allowed to repose for twenty-four hours, so that some of the bisulphite of sodium formed may crystallise. The liquid portion is then to be poured off, and stirred briskly to expel the carbonic acid. If alkaline to test paper, more sulphuric acid gas must be added ; or if acid, a little more carbonate of soda. After well stirring, the solution should only turn "blue litmus paper violet, or at most slightly red. A solution of nitrate of silver is now to be added to the above liquid, with stirring, until the precipitate at first produced begins to dissolve slowly, when the bath is ready for use. The solution thus prepared is said to be always ready for work, and " produces, quite instantaneously, a magnificent silvering upon copper, bronze, or brass articles which have been thoroughly cleansed, and passed through a weak solution of nitrate of binoxide of mercury, although this is not absolutely necessary. ' ' To keep up the strength of the bath fresh additions of nitrate of silver must be made from time to time, and after awhile some bisulphite of soda must also be added. In working this bath the solution is placed in a copper vessel, which also receiver 232 ELECTRO-DEPOSITION OF SILVER. a deposit of silver. Roseleur states that he used this bath for five years, during which period he daily silvered " as many articles as a man could conveniently carry." He also states that, without the aid of a separate current, the deposit from this solution may become nearly as thick as desired, and in direct ratio to the time of immersion. Whitening Brass Clock-Dials, &c., with the Paste. For this purpose chloride of silver and cream of tartar, with or without the addition of common salt, is made into a paste, as before described, and this should be well triturated in a mortar until it is impalpable to the touch. The paste is then spread, a little at a time, upon the brass surface which may be a clock-face or thermometer-scale, for instance and rubbed upon the metal surface with a piece of soft cork, or " velvet " cork as it is called. By thus working the silver paste over the metal it soon becomes silvered, and a coating of sufficient thickness for its purpose obtained in a very short time, according to the size of the object. When the silvering is complete the article is to be rinsed and dried in the hot sawdust. Although a very slight film of silver only is obtained in this way, its somewhat dull tone is specially ap- plicable to barometer and galvanometer scales, clock-dials, and objects of a similar nature, and, as far as its non -liability to tarnish is con- cerned, it may be considered superior to all other methods of silvering. CHAPTEE XVIII. ELECTRO -DEPOSITION OF SILVER (continued}. Preparation of New Work for the Bath. Quicking Solutions, or Mercury Dips. Potash Bath. Acid Dips. Dipping. Spoon and Fork Work. Wiring the Work. Arrangement of the Plating Bath. Plating Battery. Motion given to Articles while in the Bath. Cruet Stands, &c Tea and Coffee Services. Scratch-brushing. Preparation of New Work for the Bath. In order to insure a perfect adhesion of the silver deposit to the surface of the article coated, or plated, as it is erroneously termed, with this or any other metal, the most important consideration is absolute cleanliness. By this term we do not mean that the article should be merely clean in the ordinary sense, but that it must be what is termed chemically clean, that is, perfectly and absolutely free from any substance which would prevent the silver from attaching itself firmly to the metal to be coated. As evidence of the extreme delicacy which it is necessary to observe in this respect, we may mention that if, after an article (say a German silver spoon, for example) has been well scoured with powdered pumice and water, it be exposed to the atmosphere even for a few seconds, it becomes coated with a slight film of oxide owing to the rapidity with which copp"er (a constituent part of German silver) attracts oxygen from the air ; this effect is still more marked in the case of articles made from copper and brass. Now, this slight and almost imperceptible film is quite sufficient to prevent perfect contact between the deposited metal and that of which the article is composed. This fact, in the early days of electro -plating, created a great deal of trouble, for it was found that the work, after being silvered, was very liable to strip under the pressure of the burnisher. To overcome the difficulty, and to secure a perfect adhesion of the two metals, a third metal mercury or quicksilver which has the power of alloying itself with silver, gold, German silver, copper, and brass, was employed, and though the author for many years obtained most successful and per- fectly adherent deposits of silver without its aid, the process of quicJcing was, and still is, practised by the whole of the electro -plating trade. The silver solution which the author employed, however, and which is described in the foregoing chapter, was differently prepared 234 ELECTRO-DE POSITION OF SILVER. to those ordinarily adopted by the trade. Since the process of "quicking " is generally adopted, it mil be necessary to describe it in detail. Quicking Solutions, or Mercury Dips. This term is applied, as before hinted, to coating articles made of brass, copper, or German silver the metals most usually subjected to the process of electro- plating with a thin film of quicksilver, which may be effected by either of the following solutions : Nitrate of Mercury Dip. Put an ounce of mercury into a glass flask, and pour in an ounce of pure nitric acid diluted with three times its bulk of distilled water ; if, when the chemical action ceases, a small amount of undissolved mercury remains, add a little more acid, applying gentle heat, until the whole is dissolved. The solution is then to be poured into about I gallon of water, and well mixed by stirring. It is then ready for use, and is termed the quicking solution, or mercury dip. Articles of brass, copper, or German silver dipped into this solution at once become coated with a thin bright film of mercury. Cyanide of Mercury Dip. Dissolve one ounce of mercury as before, and dilute the solution with about I quart of distilled water. Now take a solution of cyanide of potassium, and add this gradually, stirring after each addition, until the whole of the mercury is precipitated, which may be determined by dipping a glass rod in the cyanide solution, and applying it to the clear liquor after the precipitate has subsided a little, when, if no further effect is produced, the precipitation is complete. The liquor is next to be separated by filtration. When all the liquor has passed through the filter, a little water is to be poured on to the mass, and when this has thoroughly drained off, the precipitate is to be placed in a glass or stoneware vessel, and strong solution of cyanide added, with constant stirring, until it is all dissolved, when a small excess of the cyanide solution is to be added, as also sufficient water to make up one gallon of solution. Another mercury dip is made by dissolving red precipitate (red oxide of mercury) in a solution of cyanide, afterwards diluted with water. Pernitrate of Mercury Solution. This solution is composed of Pernitrate of mercury . . . . . . i part. Sulphuric acid 2 parts. Water 1000 A very good mercury dip may be made by simply dissolving two ounces of mercury in two ounces of nitric acid, without the aid of heat; the solution thus formed is to be diluted with about three gallons of water. The quicking bath should contain just so much mercury in solution as will render a clean copper surface white almost immediately after QUICKING SOLUTIONS, OR MEECURY DIPS. 235 immersion ; if the solution be too strong, or too acid (when the nitrate of mercury solution is used), or if the solution has become nearly exhausted by use, when copper is dipped it may turn black or dark coloured instead of white, in which case the quicking bath must be rectified, otherwise it will be impossible to obtain an adherent coating of silver upon the article treated in it. As a rule, the articles merely require to become perfectly and uniformly white from the coating of mercury, but the practice is to give a stronger film to work which is required to receive a stout deposit of silver, or gold, as the case may be. When the mercury dip becomes nearly exhausted and the mercurial coating, in consequence, becomes dark coloured, the liquor should be thrown away and replaced by a new solution, which is considered better than strengthening the old liquor ; indeed, the small amount of mercury which remains in the bath after having been freely used is of so little consideration, that the liquor may be cast aside without sacri- fice the moment it gives evidence of weakness by the dark appearance of the work instead of the characteristic brightness of metallic mercury. It is a good plan to keep a quantity of concentrated mercurial solu- tion always in stock, so that when a bath becomes exhausted it may be renewed in a few minutes by simply throwing away the old liquor and adding the due proportions of strong solution and water to make up a fresh " dip." Potash Bath. To remove greasy matter communicated to the work by the polishing process, all articles to be plated must first be steeped for a short tune in a hot solution of caustic potash, for which purpose about half a pound of American potash is dissolved in each gallon of water required to make up a bath, and as this solution becomes ex- hausted by use it must receive an addition of the caustic alkali. The workman may readily determine when the solution has lost its active property by simply dipping the tip of his finger in the solution and applying it to the tip of the tongue, when, if it fails to tingle or " bite " the tongue, the solution has lost its caustic property, and may either be thrown away or strengthened by the addition of more caustic potash. When the bath has been once or twice revived in this way it is better to discard it altogether, when inactive, than to revive it. Indeed, when we consider that the object of the caustic alkali is to convert the greasy matters on the work into soap, by which they become soluble and easily removed by brushing, it will be apparent that the bath can only be effective so long as the causticity of the alkali remains. Many persons, from ignorance of this matter, have frequently used their potash baths long after they have lost their activity, and as a natural consequence the work has come out of such baths nearly in the same state as they entered it, greasy and dirty. 236 ELECTRO-DEPOSITION OP SILVER. Those who cannot conveniently obtain caustic potash (American potash, for example) may readily prepare it as follows : Obtain a few lumps of fresh lime and slake them by pouring water over them, and then covering them with a cloth ; soon after, the lime will fall into a powder, which must be made into milk of lime, as it is called, by mixing it with water to the consistence of milk or cream. A solution of pearlash is then made in boiling water, to which is added the cream of lime, and the mixture is to be boiled for at least an hour, in an iron vessel. About half or three-quarters of a pound of pearlash to each gallon should be employed, and about one-fourth less lime than potash. If the solution is thoroughly causticised, no effervescence will occur in the liquor if a drop or two of hydrochloric acid are added ; if, on the con- trary, effervescence takes place on the addition of the acid, the boiling must be continued. Acid Dips. In the preparation of certain kinds of work, acid solu- tions or mixtures are employed which may be advantageously men- tioned in this place. It is well to state, however, that after dipping the work in acid solutions it should be thoroughly rinsed in clean water, since the addition of even small quantities of acid to the alkaline plating or gilding baths would seriously injure these solutions. Indeed, careless and im- perfect rinsing must always be avoided in all de- positing operations, otherwise the baths will soon become deteriorated ; the rinsing waters should be frequently changed, and the workman taught that in this item of his labour his motto should be "water no object." Fig. 82. Nitric Acid Dip. This is frequently used for dipping copper, brass, and German silver work, and is the ordinary aquafortis of commerce, or /timing nitric acid (nitrous acid). Stoneware jugs of the form shown in Fig. 82 are used for conveying strong acids. A dipping acid, composed as follows, is also much used for producing a bright and clean surface upon certain classes of work : Nitric acid, commercial (by measure) . i . i part. Sulphuric acid . . . . ' * .2 parts. Water 2 To tnis mixture some persons add a little hydrochloric acid, and others a small quantity of nitrate of potassa (nitre). Dip for Bright Lustre. To give a bright appearance to copper, &c., the following mixture may be employed : Old aquafortis, or nitric acid dip which has been much used, i part ; water, 2 parts ; muriatic acid, 6 parts. The articles are immersed in this solution for a few ACID DIPS. 237 minutes, when they are to be briskly shaken in clean cold water, and if not sufficiently bright must be dipped again. If they become covered with a dirty deposit, the articles should be scoured with pumice and water, then Immersed in the dip for a short time and again rinsed. Another method is to first dip the articles in a weak pickle, formed by diluting old and nearly exhausted nitric acid dip with water for a few minutes, after which they are to be dipped in the same old acid dip in its undiluted condition, and finally in strong aquafortis for a moment ; they are next to be well rinsed in several waters. Dip for Dead Lustre. To produce a dead or matted surface upon copper, brass, or German silver work, the following mixture is used : Brown, or fuming aquafortis (by measure) Oil of vitriol 2 parts, i part. To the above mixture a small quantity of common salt is added. The articles are allowed to remain for some time in the dip, after which they are withdrawn and promptly dipped in the preceding liquid and immediately well rinsed. Respecting old aquafortis dips, Gore says these may be " revived to a certain extent by addition of oil of vitriol and common salt ; the sul- phuric acid decomposes the nitrate of copper in it, and also the common salt, and sets free nitric and hydrochloric acids, and crystals of sulphate of copper -form at the bottom of the liquid. All the nitric acid may be utilised in this manner." This is perfectly true, but as a rule ( acid "dips" which have become exhausted seldom produce the required brilliancy or tone of colour (when that is an object), even if strengthened by fresh ad- ditions of the concentrated acids with which they were first prepared. Zinc, tin, and lead, as also organic matter, generally find their way into these dips, and more or less interfere with the direct action of the nitric acid. Dipping. The article to be dipped should be sus- pended by a wire of the same metal, or by a wire covered with gutta-percha or india-rubber tubing, and after a moment's immersion in the acid solution, promptly plunged into clean cold water ; if the desired effect a bright or a dead lustre is not fully pro- duced by the first dip, the article must be again dipped for a moment and again rinsed. In order to remove the acid effectu- ally, several washing vessels should be at hand, into each of which the article is plunged consecutively, but the last rinsing water, more especially, should be renewed frequently. When a number of Fig. 83. =38 ELECTRO-DEPOSITION OF SILVER. small articles require to be dipped, they may be suspended from a wire, looped up as in Fig. 83, or they may be placed t a per- forated stoneware basket (Fig. 84), provided with a handle of the same material. These perforated baskets are specially manufac- tured at the potteries for acid dipping and other purposes, and if carefully treated will last for an indefinite period. The basket con- taining the articles to be dipped is plunged into the dipping acid, and moved briskly about, so as to expose every surface of the metal to the action of the acid ; as the vessel is raised the liquid escapes through the perforations, and after a brisk shaking the basket and its contents Fig. 84- Fig. 85. are plunged into the first washing water, in which it is again vigour- ously shaken, to wash away the acid as far as possible ; it is then treated in the same way in at least two more rinsing waters. The dipped articles are then to be thrown into a weak solution of crude bitartrate of potash, called aryol, to prevent them from becoming oxidised or tarnished. From this liquid they are removed as required, and again rinsed before being quicked and plated. For dipping pur- poses, stoneware and gutta-percha bowls (Fig. 85) are also used, and sometimes platinum wire trays, supported by a hook, as in Fig. 87, are employed for very small articles. Hooks of the same kind, but in Fig. 86. various forms, are likewise used for supporting various pieces of work during the dipping operations. One of these is shown in Fig. 86. Spoon and Fork Work. In large establishments this class of work may be said to hold the leading position, since, as articles of domestic utility, the spoon and fork are things of almost universal requirement. As in all other kinds of electro -plated ware and we may add everything else under the sun the silvering, or plating, is accomplished according to the requirement of the customer and the price to be paid for the work when done. In other words, the actual deposit of silver which each article receives depends upon whether it is intended to wear well, or merely required to sell. In the f ormei' SPOON AND FORK WORK. 239 case, it is usual for the customer to weigh the spoons and forks before he sends them to the plater, and again on their return, and he pays so much per ounce for the silver deposited, allowing a moderate discount from the original weight to cover any loss which may be sustained in preparing the work for the plating bath. When the goods, however, Fig. 87. are merely required to look "marketable," the amount of silver deposited upon such a class of work often ranges from little or nothing to less, if possible. Wiring the Work. Spoons and forks are first wired, as it is termed. For this purpose copper wire is cut into lengths of about 1 2 inches. A length of the wire is coiled once round the shank or narrow part of the article, and secured by twisting it several times ; the loop thus formed should be quite loose, so that the position of the spoon or fork may be easily reversed or shifted while in the plating vat, to equalise the deposit, and to allow the parts where the wire has been in contact to become coated with silver. The copper wire used for "slinging" is usually about No. 20 B.W.G. (Birmingham Wire Gauge), which is the gauge most generally adopted in this country. The spoons, &c., are next placed in the hot potash bath, where they are allowed to remain for a short time, when they are removed, a few at a time, and rinsed in cold water. They are next to be brushed or scoured all over with fine pumice-powder moistened with water, and then thrown into clean water, where they remain until a sufficient number have been scoured, when these are taken out by their wires and im- mersed in the quicking solution, which, for spoon work, may con- veniently be in a shallow oval pan of the form shown in Fig. 88. After remaining in the quicking bath a short time, they are examined, and if sufficiently quicked, and uniformly bright, like quicksilver, they are rinsed in water and at once suspended in the 240 ELECTRO-DEPOSITION OF SILVER. plating tank, as close together as possible without touching. When the bath is filled with work, the spoons or forks should be turned upside down by slipping the shank through the loop ; and the work- man who does this must be very careful to handle them as little as possible, and only to grip them with the fingers by the edges, which an experienced plater will do with great smartness, and with very trifling contact with his fingers. The objects of thus changing the position of the work are twofold, namely, to allow the wire mark to become coated with silver, and to equalise the deposit, which always takes place more energetically at the lower end of the article while in the bath. This system of shifting should be repeatedly effected until the required deposit is obtained. When shifting the spoons, &c., all that is necessary is to raise the straight portion of the suspending wire which is above the solution with one hand, which brings, say, the handle of the spoon, out of the solution ; if this be now gripped between the finger and thumb of the other hand at its edges, and raised until the bowl end touches the loop, by simply turning the spoon round its bowl will be uppermost, in which position the article is carefully but quickly lowered into the bath again. Another method of suspending spoons and forks in the plating bath is the following : Copper wire, about the thickness of ordinary bell wire, is cut up into suitable lengths, and which will depend upon the distance between the negative conducting -rod and the surface of the silver solution. These wires are next to be bent into the form of a hook at one end, and at the other end is formed a loop, as in Fig. 89, leaving an opening through which the shank of a spoon or fork may pass into the ring or loop and be supported by it. To prevent the silver from being deposited upon the vertical portion of the wire, where it would be useless and unnecessary, this portion of the wire should be protected by means of glass, Fig. 89. gutta-percha, or vulcanised india-rubber tubing, which is slipped over the wire before the upper hook is formed. After being some time in use, the lower ring becomes thickly coated with a crystalline deposit of pure silver, when these wires must be replaced by new ones, and the insulating tubes may be again applied after removal from the old wires. Ordinary slinging wires, as those previously described, should never be used more than once, and for this reason : when a certain amount of silver or other metal is deposited upon wire except under certain conditions it is invariably more or less brittle, and in attempting to twist it round an article it is very liable to break, often causing the article to fall from the hand perhaps into the bath and rendering the silver-covered fragments of wire liable to be wasted by being- ARRANGEMENT OF THE PLATING BATH. 241 swept away with the dirt of the floor. It is more economical to employ fresh wires for each batch of work, and to strip the silver or other metal from the wires by either of the processes hereafter given, by which not only may all the metal be recovered, but by annealing, cleaning, and straightening the wires, they may* be used again and again. Moreover, a wire that has been twisted once becomes hardened at that part, and cannot with safety be twisted again without being annealed. Arrangement of the Plating Bath. The size and form of deposit- ing tanks for silver plating vary in different establishments, as also does the material of which they are constructed. For small quanti- ties of silver solution, say from ten up to thirty gallons, oval stone- ware pans may be used, and with ordinary care will last a great number of years. Wooden tubs, if absolutely clean, may also be em- ployed for small operations, but since that material absorbs the silver solution, such vessels should be well soaked with hot water before pouring in the solution. Tanks made from slate, with india-rubber joints, have also been much used in silver- plating. Very good plating tanks may be made in the same way as directed for nickel - plating baths, that is, an outer vessel of wood, secured by Fig. 90. screwed bolts, lined with sheet lead, and re -lined with matched board- ing. Wrought-iron tanks, lined with wood, are, however, greatly pre- ferred, and when properly constructed and lined, form the most durable of all vessels for solutions of this description. Depositing tanks for large operations are usually about six feet in length, three feet in width, and about two feet six inches in depth, and hold from two to three hundred gallons of solution ; tanks of greater length are, however, sometimes employed. An ordinary wrought-iron plating tank is shown in Fig. 90, in which also the arrangement of the silver anodes and sundry articles in solution is seen. The upper rim of the tank is furnished with a flange of wood, firmly fixed in its position, upon which rest two rectangles of brass tubing or stout copper rod. The outer rectangle frequently consists of brass tubing about an inch in diameter, at one corner of which a binding screw is attached, by means of solder, for connecting it with the positive pole of the battery 242 ELECTRO-DEPOSITION OP SILVER. or other generator of electricity. The inner rectangle should be of stout copper rod, or wire usually about one -half the thickness of the former, and is also provided with a binding screw at one corner, to connect it with the negative pole of the battery. A series of brass rods, from half to one inch in diameter, and each about the length of the tank's width, are laid across the outer rectangle, and from these are suspended the silver anodes ; similar but shorter rods of brass are placed between each pair of anodes, and rest upon the inner rectangle ; from these rods the articles to be plated are suspended, as shown in the engraving. Before the respective conducting rods are placed in position, they must be thoroughly well cleaned with emery cloth, as also must be the rectangular conductors and wire holes of binding screws which are to receive the positive and negative conducting wires, the ends of which must likewise be cleaned with emery cloth each time before making connection with the battery. It may be well here to remark that all the -points of connec- tion between the various rods, wires, and binding screws must be kept perfectly clean, otherwise the electric current will be obstructed in its passage. When the conducting rods become foul by being splashed with the cyanide solution, they should be well cleaned with emery cloth, and the operation of cleaning these rods should always be performed each morning before the first batch of work is placed in the solution ; the emery cloth should only be applied when the conducting rods are perfectly dry. It is always a characteristic of a really good plater that all his conducting rods are kept bright and clean, and every appliance in its proper place. Plating Battery. The most useful form of battery for depositing silver, either upon a large or small scale, is a modification of the Wollaston battery shown in Fig. 91. For depositing upon a large scale, a stone jar capable of holding about ten gallons forms the battery cell. A bar of wood, D, having a groove cut in it, so as to allow a stout plate of zino to pass freely through it, rests across the battery jar, A. Two sheets of copper, B b, connected by strips of the same metal soldered to the upper corners, are placed over the wooden bar, and a binding screw connected to one of the copper plates, either by means of solder or by a side screw. The copper plates should nearly reach to the bottom of the jar. A suitable binding screw is attached to the zinc plate, c, which must be well amal- gamated. The exciting fluid consists of dilute sulphuric acid, in the proportion of one part of the latter to fifteen parts of cold water. To Fig. 91. Fig. 92. PLATING BATTEEY. 243 prevent the zinc from coming in contact with the copper plates, a small block of wood, having a tolerably deep groove of the same width as the thickness of the sheet of copper, may be fixed on to each edge of the pair of plates about midway between the top and the bot- tom. In order to regulate the amount of current in working these batteries, it is commonly the practice to drill a hole in the centre of the upper part of the zinc plate, to which a strong cord is attached, and allowed to pass over a pulley, the other end of the cord being con- nected to a counterweight. A windlass arrangement, as in Fig. 92, is also used for this purpose, by which the zinc plate can be raised and lowered by simply turning a handle connected to a revolving spindle, supported by up- rights of wood, round whicn the cord becomes wound or unwound according to the motion given to the handle. When the bath is about to be filled with work, the zinc plate should only be lowered a short distance into the acid solution, and the surface is to be increased as the filling of the bath progresses ; if this precaution is not observed, the deposition will take place too rapidly upon the work, and the deposited metal will assume a grey colour instead of the characteristic white, besides which the silver will be liable to strip or separate from the underlying metal in the subsequent pro- cesses of scratch-brushing and burnishing, or even under the less severe process of polishing. A very safe way to check the too rapid deposit, is to suspend an anode from the negative conducting rod as a cathode when the first batch of articles is being placed in the bath. When very powerful batteries or dynamo -machines are used, the resistance coil (vide Nickel-plating) must be employed. '.-. Motion given to Articles while in the Bath. In order to insure uniformity of deposit while employing strong electric power from magneto or dynamo machines, it has been found that by keeping the articles slowly in motion while deposition is taking place, this desirable end can be effectually attained. There are several ingenious devices adopted for this purpose, to several of which we may now direct attention. It is a fact that deposition takes place first at the extreme end of the article in solution that is the point farthest from the source of electricity ; * and this being so, we may be sure that the deposition * Except in electrotyping, in which case the surface which receives the deposit (plumbago) is but an indifferent conductor of electricity. 244 ELECTRO-DEPOSITION OF SILVER. progresses in the same ratio during the whole time the articles are receiving the deposited metal provided the solution and the work remain undisturbed. Indeed, in the case of table forks, if we suffer them to remain, with their prongs downward, undisturbed for a con- siderable time, we shall find, on removing them from the bath, that the prongs, from the extreme tips upward, will be coated with a crystalline or granular deposit, while the extreme upper portion of the article will be but poorly coated. In no case is the fact of the deposit taking place from the lowest part of an article upward more practi- cally illustrated than in the process of "stripping" (to which we shall refer hereafter) or dissolving the silver from the surface of plated articles, when, after they have been in the stripping solution for some time, we find that the last particles of silver which will yield to the Fig. 93- chemical action of the liquid are the points of the prongs of a fork, the lowest part of the bowl of a spoon, as also (if the articles have been duly shifted during the plating) the extreme ends of the handles of either article. 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 three inches in diameter connected to it, which slowly travel to and fro to the extent of three or four inches upon inclined rails attached to the upper edges of the tank, the motion, which is both horizontal and vertical, being given by means of an eccentric wheel driven by steam power. By another arrangement, the articles are Suspended from a frame (as in Fig. 93), and the motion given by the eccentric wheel as shown in the engraving. The simplicity of the former arrangement, however, will be at once apparent. Cruet Stands, &c. Before being submitted to the cleansing opera- CEUET STANDS, ETC. 245 tions, quicking, &c., before described, the " wires " of cruet and liqueur stands must be separated from the bottoms, to which they are generally connected by small nuts, and these latter should be slung- upon a wire and laid aside until the other parts of the article are ready for plating. A wire is then to be connected to each part of the cruet frame, and these are then to be immersed in the hot potash liquor, being left therein sufficiently long to dissolve or loosen any greasy matter which may attach to them. After being rinsed, they are to be well brushed with powdered pumice and water. The brushes used for this and similar purposes are made from hog hair, and are supplied with one or more rows, to suit the various purposes for which they are required ; for example, a one-rowed brush is very useful for cleaning the joints connecting the rings with the framework of cruet stands, as also for all crevices which cannot be reached by a wider tool ; a two- rowed brush is useful for crevices of greater extent and for hollows ; and three, four, five, and six-rowed brushes for flat surfaces, embossed work, and so on. One of these useful tools is shown in Fig. 94. Fig 94- After scouring and rinsing, the parts of the cruet stand or liqueur ' stand are to be immersed in the quicking solution until uniformly white in every part, after which they must be well rinsed and immedi- ately put into the plating bath ; after a short immersion, the pieces should be gently shaken, so as to shift the slinging wire from its point of contact, and thus enable that spot to become coated with silver ; it is always advisable to repeatedly change the position of the wire so as to avoid the formation of what is termed a wire mark, and which is of course due to the deposit not taking place at the spot where the wire touches the article, thereby leaving a depression when the article is fully plated. The flat base of the cruet stand should be suspended by two wires, each being passed through one of the holes at the corner, and it should be slung sideways and not lengthwise ; its position in the bath should be reversed occa- sionally, so as to render the deposit as uniform as possible ; the same observation applies to the " wire " part of the cruet stand. When mounts are sent with the cruet stand, not sepa- rate, but cemented to the cruets, which is often the case, it will be well, if it can be conveniently done, to remove the pin which connects the top or cover with the rim of the mustard mount, so as to plate these parts separately, otherwise the cover will require shifting 1 246 ELECTRO-DEPOSITION OP SILVER. repeatedly in order to allow those parts of the joint which are pro- tected from receiving the deposit when the cover is open, to become duly coated. Tea and Coffee Services. Like the foregoing articles, these are of very variable design, and are either plain, chased and embossed, or simply engraved. Unless sent direct from the manufacturer in the proper condition for plating that is, with their handles and covers unfixed it will be better to remove the pins connecting these parts with the bodies of tea and coffee pots before doing anything else to them, unless, as is sometimes the case, they are so well riveted as to render their severance a matter of difficulty. The disadvantages attending the plating of these vessels with their handles and lids on are that the solution is apt to get inside the sockets of the handles, and to ooze out at the joints when the article is finished, while the joint which unites the lid with the body can only be properly plated when the lid is shut, at which time the interior of the lid can receive no deposit. When sent to the plater by the manufacturer, the various parts are usually either separate, or merely held to- gether by long pins, which may readily be withdrawn by a pair of pliers, and the parts again put together in the same way when the articles are plated and finished that is burnished or polished, as the case may be. In plating work of this description, the articles are potashed, scoured and quicked as before, and when ready for the plating bath, the tea and coffee pots are generally wired by passing the slinging wire through the rivet-holes of the joints ; but in order to equalise the deposit as far as possible, it is a good plan, after the article has received a certain amount of deposit, to make a loop at one end of a copper wire, and to pass it under one of the feet of the teapot, then to raise the vessel somewhat, and connect the other end of the wire with the conducting rod ; care must be taken, however, not to let the wire touch the body of the vessel, or if it does so, to shift it frequently. Since deposition always takes place more fully at the points and projections of an article, it will be readily understood that the inte- riors of vessels being also out of electrical sight, so to speak, of the anodes will receive little if .any deposit of silver. This being the case, if we wish to do the work thoroughly well in every part, it will be necessary to deposit a coating of silver upon the inside either before or after the exterior has been plated. To do this, the vessel being well cleaned inside, is placed upright on a level bench, and a wire connected to the negative pole of the battery is slipped through the joint as before. A small silver anode, being either a strip of the metal or a narrow cylinder, is to be attached to the positive pole, and the anode lowered into the hollow of the vessel, care being taken that SCEATCH-BEUSHINa. 247 it does not touch in any part. The vessel is then to be filled to the top with silver solution dipped out of the bath with a jug, and the whole allowed to rest for half an hour or so, at the end of which time the interior will generally have received a sufficient coating of silver. Scratch-brushing. One of the most important mechanical opera- tions connected with silver-plating is that of scratch-brushing. For this purpose skeins of thin brass wire, bound round with stout brass or copper wire (Fig. 97), are used. When the plated articles are removed from the bath, they present a pearly white appearance not unlike very fine porcelain ware, but still more closely resembling standard silver that has been heated and pickled in dilute sulphuric acid, as in the process of whitening watch dials. The dead white lustre of electro - deposited silver is due to the metal being deposited in a crystalline form, and the dulness is of so fugitive a nature that even scratch- ing the surface with the finger nail will render the part more or less bright by burnishing the soft and delicate crystalline texture of the deposit. The object of scratch- brushing is to obliterate the white " burr," as it is called, before the work is placed in the hands of the burnisher or polisher, otherwise it would be apt to show in such parts of the finished article as could not be reached by the tools employed in those operations. As in the case of gilding, the revolving scratch -brushes are kept con- stantly wetted by a thin stream of stale beer, or half beer and water, supplied, by means of a tap, from a small vessel (which may conveniently be a wooden bucket) placed on the top of the scratch - brush box. A tin can, or other light vessel, stands upon the floor, beneath the box, to catch the beer runnings, which escape through a pipe let into a hole in the bottom of the box. A still more handy plan is to have a small hook fixed below the right-hand corner of the scratch -brush box, for supporting a tin can or other vessel ; and by giving the box a slight inclination forwards, and towards the right- hand corner, the liquor will flow out through a hole at the corner, in 95- 248 ELECTRO-DEPOSITION OF SILVER. which a short piece of lead pipe should be inserted. By this arrange- ment (Fig. 95), the workman can empty the can into the vessel above, whenever the beer liquor ceases to drip upon the scratch -brushes, without allowing the driving wheel to stop. Much time may be saved ki this way, especially when the liquid happens to run short, at which time the can requires to be emptied frequently. To prevent the beer runnings from overflowing, and thus making a mess on the floor, while wasting the liquor, no more liquor should be put into the cistern above than the vessel be- low will contain. A quart or three-pint can full will be quite sufficient for ordinary work, and a vessel of this latter capacity will be quite as large as the workman can manipulate readily without stopping the lathe. The lathe scratch-brush consists of a series of six or eight scratch- brushes (according to the number of grooves in the " chuck ") bound to the chuck by strong cord, as in Fig. 96. Previous to fixing the brushes, the skein of fine brass wire forming a single scratch -brush, Fig. 97, is to be cut with a pair of shears or strong scissors. Before applying the compound brush which is connected to the lathe -head by means of its screwed socket to the plated work, the brushes should be opened, or spread, by pressing rather hard upon them, while revolving, with a piece of stout metal, or the handle of one of the cleaning brushes ; this will spread the bundles of wire into a brush -like form suitable for the purpose to which they are to be applied. It may be well to state that the revolving scratch-brush should on no account be applied to the work in a dry state, but only when the beer liquor is running suffi- ciently free to keep the brushes wet. In working the scratch -brush, it must be allowed to re- volve to the right of the operator, otherwise the " chuck " will be liable to come unscrewed ; moreover, this is the most con- venient motion for enabling the workman to guide the articles without risk of their being jerked out of his hand an acci- dent that might readily occur if he inadvertently turned the F\a Q7 wheel the wrong way. In scratch -brushing spoons and forks, ' a very moderate pressure is all that is necessary to render the surface bright ; a little more pressure, however, is required for the edges of salvers, dishes, handles and feet of cruet stands, and other work in which hollows of some depth form a necessary feature of the ornamental mounts. PLATING- BY DYNAMO-ELECTEICITY. 249 Plating by Dynamo-Electricity. In the larger electro -plating establishments, magneto or dynamo -electric machines are employed, and the current from these powerful machines is conveyed by stout leading wires to the various baths, the force of the current entering the baths being regulated by resistance coils. In works of moderate dimensions, a good machine, either of the magneto or dynamo -electric type, will supply sufficient electricity to work a large bath of each of the following solutions : nickel, silver, brass and copper, as also a good -sized gold bath. In working with these machines, it is of the greatest importance that they should be driven at an uniform speed ; and though some machines require to be driven at a higher rate of speed than others, the maximum allowed by the respective makers should never be exceeded, or the machine may become considerably heated and seriously injured. "When start- ing the machine, the number of its revolutions should be ascertained by means of the speed indicator referred to elsewhere, and as far as practicable the normal speed should be maintained without sensible variation while the current is passing into the vats. Although this uniformity of speed is more certainly obtained, we believe, with gas engines than with steam power, if proper care and attention are given, and frequent examination of the speed of the dynamo -armature made by the plater, tolerable regularity may be attained from the latter source of power. It must always be remembered by the plater, that when the engine which drives the dynamo is also employed for driving polishing lathes, emery wheels, &c., when very heavy pieces are being treated in the polishing shop the speed of the dynamo may be greatly influenced ; indeed we have frequently known the belt to be suddenly thrown off the pulley of a dynamo from this cause, and the machine, of course, brought to a full stop. CHAPTER XIX. ELECTRO -DEPOSITION OF SILVER (continued). Plating Britannia Metal, &c Plating Zinc, Iron, &c . Replating Old Work. Preparation of Old Plated Ware. Stripping Silver from Old Plated Articles. Stripping Gold from Old Plated Articles. Hand Polishing. Resilvering Electro-plate. Characteristics of Electro-plate. Deposit- ing Silver by Weight. Roseleur's Argyrometric Scale. Solid Silver Deposits. On the Thickness of Electro-deposited Silver. Pyro-plating. Whitening Electro-plated Articles. Whitening Silver Work. Plating Britannia Metal, &c. It was formerly the practice to give a coating of copper or brass to articles made from Britannia metal, tin, lead, or pewter, since it was found difficult otherwise to plate such metals and alloys successfully, that is without being liable to strip. It is usual now, however, to immerse the articles first in the hot potash solution, and to place them, with or without previous rinsing, in the depositing -bath. Since the potash bath dissolves a small quantity of metal from the surface of articles made from these metals, a favourable surface is left for the reception of the silver deposit, to which the metal adheres tolerably well indeed sufficiently so to bear the pressure of the burnishing tools. Since Britannia metal, pewter, &c., are not such good conductors of electricity as German silver, copper, or brass, an energetic current must be applied when the articles are first immersed in the bath, and when the whole surface of each article is perfectly coated with silver, the amount of current may be somewhat diminished for a time, and again augmented as the deposit becomes stouter ; care being taken not to employ too strong a current, however, in any stage of the plating process. It may be mentioned that articles made from Britannia metal which, are generally sold at a very low price are seldom honoured with more than a mere film of silver, in fact just so much as will render them marketable, and no more ; still, however, a very extensive trade is done in work of this description, much of which presents an exceed- ingly creditable appearance. Plating Zinc, Iron, &c. To coat these metals with silver, it is best to first give them a slight coating of brass or copper, in an alka- line solution, which does not occupy much time, neither is it a costly REFLATING OLD WORK. 251 proceeding. Both these metals adhere pretty firmly to zinc, iron, and steel, while silver attaches itself freely to brass and copper. If hot solutions of copper or brass are used, the trifling deposit required to enable the subsequent coating of silver to adhere to the zinc, &c., can be obtained in a very few minutes. Each opera- tion, however, should follow in quick and unbroken succession, for if the brass or copper-coated article be allowed to remain, even for a few seconds, in the air before being placed in the silver bath, it will rapidly oxidise, and render the deposited silver liable to strip when the article is scratch-brushed. Moreover, if the brassed or coppered articles are allowed to remain for a short time in the air while in a moist condition, voltaic action will be set up between the zinc and the metallic covering, by which the latter will become loosened, and will readily peel off under the action of the scratch-brush. Each article, after being brassed or coppered, should, after rinsing, be placed at once in the silvering-bath. Replating Old Work. Under this head must be considered not only the old Sheffield and Birmingham ware, the manufacture of which became superseded by the electro -plating process, but also the more modern article known as " electro -plate " (the basis of which is German silver), which has, by domestic use, become unsightly in con- sequence of the silver having worn off the edges and other prominent parts most subject to friction in the process of cleaning. In the busi- ness of replating, there must ever be a constant if not a growing trade, if we consider the enormous quantity of plated goods which annually flow into the market, and which must even the best of it require resilvering at some time or other, while the inferior classes of goods may require the services of the electro -plater at a much earlier period than the purchaser of the articles expected. Preparation of Old "Plated" Ware for Resilvering. These articles, whether of Sheffield or Birmingham manufacture, have a basis of copper. The better class of plated ware, which was originally sold at about half the price of standard silver, and some of which may be occasionally met with, though doubtless becoming rarer every year, is of most excellent quality, both as to design and workmanship, and when properly prepared for replating, and well silvered and finished after, is well worthy of being replaced upon the table by the side of the more modern articles of electro -plate. Such articles, however, should never be replated with an insignificant coating of silver, since the copper surface beneath would soon reappear and expose the indif- ferent quality of the plater's work. It may be well to state, however, that by far the greater proportion of old " plated " articles are not of the same quality as the old Sheffield plate and the equally admirable work formerly manufackired by the distinguished firm of Boulton and 252 ELECTRO-DEPOSITION OF SILVER. Watt, of Birmingham, some specimens of which may also be occa- sionally met with ; but a very inferior class of goods, which may generally be recognised by their having lost nearly the whole of their silver covering which was never very much whereas in the better class of old plated ware the silver has worn off chiefly at the extreme edges, while the remainder of the article retains a sound coating of silver. In preparing old plated cruet frames, &c., for replating, the wires, which are generally attached by soft solder to the stands, must be separated by first scraping the solder clean, and then applying a hot soldering-iron (using a little powdered resin), which must be done very carefully, otherwise the solder which connects the feet of the stand may become melted, causing them to drop off ; it is safer, when applying the hot iron, to have an assistant at hand, who with a brush or hare's foot should wipe away the solder from the joint when it is melted. All the joints being treated in this way, in the first instance, the ground is cleared, when by a fresh application of the soldering- iron the legs of the wire may be loosened, one at a time, until the whole series have become partially displaced, after which, by again applying the hot iron, the legs, one after another, may be forced out. If the two parts of the frame are not taken asunder in this cautious way, the workman may involve himself in much trouble from the melting of the lead mounts (called " silver " mounts), the dropping off of legs, feet, &c., all of which may be avoided in the way we have suggested. It must be understood that our suggestions are specially made for the guidance of those who, though good platers, may not be experts in the application of the soldering-iron. It is usually the practice to remove what silver there may be upon old plated articles by the process termed " stripping." This consists in immersing the article in a hot acid liquid which, while dissolving the silver from the surface, acts but little upon the underlying metal, whether it be of copper, brass, or German silver. The process of stripping being an important auxiliary in connection with the replating of old work, as also in cases in which an unsuccessful deposit has been obtained upon new work, we may advantageously describe the process at once ; but previous to doing so, we may state that the silver removed by stripping from the better class of old plated articles is sometimes an important gain to the electro -plater, if he be fortunate enough to receive a liberal amount of such work, while, on the other hand, the inferior qualities of .plated ware will yield him no such satisfaction. Stripping Silver from Old Plated Articles. A stripping -bath is first made by pouring a sufficient quantity of strong oil of vitriol into a suitable stoneware vessel, which must be made hot, either by means of a sand bath, or in any other convenient way. To this must be added a small quantity of either nitrate of potash, or nitrate of soda, STRIPPING OLD PLATED ARTICLES. 253 and the mixture stirred with a stout glass rod until the latter is dis- solved. The article to be stripped is first slung upon a stout copper wire ; it is then to be lowered in the liquid, being held by the wire, until wholly immersed. Leave the article thus for a few moments, then raise it out of the solution, and observe if the silver has been partially removed ; then redip the article and leave it in the bath for a short time longer, then examine it again ; if the action appears rather slow, add a little more nitre, and again immerse the article. When the silver appears to be dissolving off pretty freely, the opera- tion must be watched with care, by dipping the article up and down in the solution, and looking at it occasionally, and the operation must be kept up until all the silver has disappeared, leaving a bare copper surface. When a large number of articles have to be stripped, a good many of these may be placed in a hot acid bath at the same time, but since they will doubtless vary greatly in the proportion of silver upon them, they should be constantly examined, and those which are first stripped, or desilvered, must be at once removed and plunged into cold water. When all the articles are thoroughly freed from silver, and well rinsed, they are to be prepared for plating by first buffing them, as described in the chapter on polishing, after which they are cleaned and quicked in the same way as new work. A Cold Stripping Solution, which is not so quick in its action as the former, is made by putting in a stoneware vessel a quantity of strong sulphuric acid, to which is added concentrated nitric acid in the pro- portion of I part of the latter acid to 10 parts of the former (by measure). In this mixture the articles are suspended until they give signs of being nearly deprived of their silver, when they are somewhat more closely attended to until the removal of the silver is complete, when they are at once placed in cold water. The articles must be perfectly dry when placed in this stripping liquid, since the presence of even a small quantity of water will cause the acid to attack the copper, brass, or German silver, of which the articles may be made. The vessel should also be kept constantly covered, since sulphuric acid attracts moisture from the air. The silver may be recovered from old stripping solutions by either of the methods described elsewhere. Buffing Old Work after Stripping. The stripped articles, after being thoroughly well rinsed and dried, are sent to the polishing shop, where they are buffed and finished, and the cavities, caused by the action of vinegar or other condiments upon the base of cruet stands, as far as possible removed. Sometimes these depressions are so deep that. they cannot be wholly removed without rendering the surface so thin that, in burnishing this portion of the article, it is liable to warp or become stretched, rendering the flat surface unsightly for ever after. The back of the stand, which is usually coated with tin, should be roughly 254 ELECTRO-DEPOSITION OF SILVER. "bobbed" with sand until all the tin is removed. The next items, which usually give some trouble, are the so-called " silver mounts," which are commonly of two kinds. The edge, or border of the stand, being originally a shell of silver foil, struck in design, and filled or backed up with lead or solder, is generally more or less free from silver, except in the hollows ; and since the soft metal does not receive the silver deposit so favourably as the metal of which the rest of the article is composed, these edges must receive special treatment, other- wise the silver deposited upon them will be brushed off in the after- process of scratch-brushing. There are several ways of treating ' ' leao 1 edges," as they are properly called. Some persons remove them alto- gether, and replace them by brass mounts, which are specially sold foi this purpose. If this plan be not adopted, we must endeavour to induce the silver to adhere to the lead mounts by some means or other. The edge of the article, after being cleaned, may be suspended, one angle at a time, in a brassing bath, or alkaline coppering solution, until a film of either metal is deposited upon the leaden mount, when, after being rinsed, a second angle may be treated in the same way, and so on, until the entire edge is brassed or coppered. The small amount of brass or copper, as the case may be, which may have deposited upon the plain portions of the work, may be removed by means of a soft piece of wood, powdered pumice, and water. Edges treated in this way generally receive a good adherent coating of silver. Sometimes, but not always, the ordinary "quicking" will assist the adhesion of the silver to the lead mounts. Another method of depositing a firm coating of copper upon lead edges is to put a weak acid solution of sulphate of copper in a shallow vessel, and having a small piece of iron rod in one hand, to lower one portion of the edge of the cruet bottom into the solution ; then touching the article under the liquid, in a short time a bright coating of copper will be deposited upon the leaden surfaces, by means of the voltaic action thus set up, when this portion may be rinsed, and the remainder treated in the same way. Or take a small piece of copper, and connect it by a wire to the positive electrode of a battery, envelop this copper in a piece of chamois leather or rag, then put the article in connection with the negative electrode. By dipping the pad, or " doctor," in either an acid or an alkaline solution of copper, or in a warm brassing solution, and applying it to the part required to be coated, a deposit will at once take place, which may be strengthened by repeatedly dipping the pad in the solution and applying again. In this way, by moving the pad containing the small anode of copper or brass along the edge, the required deposit may be effected in a very short time with a battery of good power a Bunsen cell, for example. Old " plated " tea and coffee pots are invariably coated inside with OLD PLATED AETICLES. 255 tin ; and if this part of the article is required to be silvered which is sometimes, though not always, the case the tin should first be removed by dissolving it in some menstruum which will not dissolve the copper beneath. For this purpose either hydrochloric acid or a solution of caustic potash may be used. If the former, the inside of the vessel should first be filled with a boiling hot solution of potash, and after a time the liquid is to be poured out and thoroughly rinsed. It must then be filled with strong muriatic acid, and allowed to rest until the upper surface, upon being rubbed with a strip of wood, exposes the copper, when the acid is to be poured out, and the vessel again rinsed. The inside must now be cleaned by brushing with silver sand and water as far as the brush will reach, when the bottom and hollow parts of the body may be scoured with a mop made with rag or pieces of cloth and silver sand. If it is preferred to dissolve the tin from the inside of the vessel by means of potash, the hot liquid must be poured in as before, and the vessel placed where the heat can be kept up until the desired object the removal of the tin is attained, when the vessel must be cleaned as before. Dissolving the tin from the inside of such old plated articles should be the first preparatory process they are subjected to ; indeed, the interiors of all vessels to be electro -plated should be attended to first, in all the preliminary opera- tions, but more especially in the operations of scouring, in which the handling of the outside, though a necessity, is liable to cause the work to strip (especially in nickel-plating), unless the hands are kept well charged with the pumice or other gritty matter used in scouring. To remove tin from copper surfaces, a hot solution of perchloride of iron may also be used, for although this iron salt acts freely upon copper, voltaic action is at once set up when the two metals, tin and copper, come in contact with the hot solution of the perchloride, which quickly loosens the tin so that it may be brushed away with perfect ease. From the rapidity of its action, we should prefer to adopt the latter mode of de-tinning copper articles, but either of the former would be safest in the hands of careless or inexperienced manipu- lators. Old " plated " we use the term in reference to Sheffield ware more especially sugar-bowls, cream-ewers, mugs, goblets, &c., which have been gilt inside, should have what gold may still remain upon the article " stripped off " before other operations are proceeded with ; and since these articles were originally mercury gilt, in which a liberal amount of gold was often employed, it is frequently worth while to remove this by dissolving it from the insides of the vessels ; and the same practice should be adopted with all silver- gilt articles which are merely required to be whitened, to which we shall refer in another place. 256 ELECTRO-DEPOSITION OP SILVER. Stripping Gold from the Insides of Flated Articles. The sugar-bowl or other vessel is placed on a level table or bench, and put in connection with the positive electrode of a battery. A strip of sheet copper or platinum foil is next to be attached to the negative electrode, and placed inside the vessel, without touching at any point. By this arrangement the article becomes an anode. The vessel must now be filled with a moderately strong solution of cyanide of potas- sium, consisting of about 4 ounces of cyanide to I quart of water. Since the metal beneath will also dissolve in the cyanide solution, the operation must be stopped as soon so the gold has disappeared from the surface. The solution should then be poured out, and bottled for future use. When the stripping solution, from frequent use, has acquired sufficient gold to make it worth while to do so, the metal may be extracted by any of the processes given in another chapter. Old plated table candlesticks, some of which are of admirable design and well put together, may be occasionally met with, as also a very inferior article, the parts of which are mainly held together by a lining or " filling " of pitch, or some resinous compound. In treating old plated candlesticks, the removal of the filling should be the first consideration, since it will give the plater a vast amount of after trouble if he attempts to plate them while the resinous or other matter remains in the interior. In the first place, the silver solution will be sure to find its way into the hollow of the article, from which it will be next to impossible to entirely extract it when the article is plated, for the liquid will continue to slowly exude for days, or even weeks, after the article is finished. Again, if the article be plated without removing the filling material, this, being freely acted upon by the cyanide solution, will surely harm it. After removing the socket, the green baize or cloth should be removed from the base of the candle- stick, when it should be placed before a fire until the whole of the resinous matter or pitch has run out. To facilitate this, the article should be slightly inclined in an iron tray or other vessel, so that the resinous matter may freely ooze out and be collected. In dealing with the inferior varieties of candlesticks which may be known by all or nearly all the silver having worn from their surface the plater may find, to his chagrin, that before all the stuffing has runout the candle- stick will have literally fallen to pieces. The various parts, not having been originally put together with solder, but held in position merely by the filling material, readily come asunder when the internal lining is loosened. In such a case as this he should, without losing his temper (if possible), determine to prepare and plate all the parts separately (keeping the parts of each "stick" together), and after scratch-brushing, carefully put them together again. The candlestick should now be turned upside down, and held in this position by an HAND POLISHING. 257 assistant, while a sufficient quantity of pitch (previously melted in an earthenware pipkin) is poured in. The candlestick must be left in the erect position until the fining has nearly set, when the hollow formed by the contraction of this substance must be filled up with the same material, and the article then left until quite cold, when it may be handed over to the burnisher. When burnished, the surface of the pitch should be levelled with a hot iron, and then at once brought in contact with a piece of green baize, placed upon a table, and gentle pressure applied to cause the uniform adhesion of the two surfaces. When cold, the remainder of the baize is cut away by means of a sharp pair of scissors, when, after being wiped with a clean or slightly rouged chamois leather, the article is finished. Hand Polishing. When the electro -plater is unprovided with a proper polishing lathe and the various appliances ordinarily used in polishing metals, he must have recourse to the best substitute he can command for polishing by hand. To aid those who may be thus cir- cumstanced, and who may have no special knowledge of the means by which the rough surfaces of old work may be rendered sufficiently smooth for replating, we will give the following hints : Procure a few sheets of emery-cloth, from numbers o to 2 inclusive ; one or two lumps of pumice-atone ; a piece of Water-of-Ayr stone, about f inch square and 5 inches long ; also a little good rottenstone, and a small quantity of sweet oil. Suppose it is necessary to render smooth the base, or stand, of an old cruet frame, deeply marked on its plane sur- face by the corrosive, or, rather, voltaic action of the vinegar dropping from the cruets upon the plated surface. The article, after being ttripped, as before, should be laid upon a solid bench, and a lump of pumice (previously rubbed flat upon its broadest part) frequently dipped in water and well rubbed over the whole surface, that is, not merely where the cavities are most visible, but all over. After thus rubbing for some time, the stand is to be rinsed, so that the operator may see how far his labour has succeeded in reducing the depth of the " pit-marks." The stoning must then be resumed, and when the surface appears tolerably uniform, the article should be well rinsed, dried, and again examined, when if the marks are considerably obliterated, a piece of No. 2 emery-cloth may be briskly applied to the surface by being placed over a large cork or bung, after which a finer emery-cloth should be applied. The article should next be thoroughly rinsed, and brushed with water to remove all particles of emery ; and while still wet, the Water-of-Ayr stone must be rubbed over the surface. The stone should be held in an inclined position, frequently dipped in water, and passed from end to end of the article. The effect of this will be and must be to remove all the scratches or marks produced by the pumice and emery-cloth. Until these have 2f>8 ELECTRO-DEPOSITION OP SILVER. disappeared, the smooth but keenly -cutting stone must be applied. After having rendered the surface perfectly smooth, the article is to be again rinsed and dried. It must now be briskly rubbed with rotten- stone, moistened with oil, and applied with a piece of buff, or belt (such as soldiers' belts are made of), glued to a piece of wood. When sufficiently rubbed or buffed with the rottenstone, the surface will be bright, and in order to ascertain how the work progresses, it should occasionally be wiped with a piece of rag. In very old plated articles, the pit-holes are frequently so deep that to entirely obliterate them would render the metal so thin as to spoil the article. It is better, therefore, not to go too far in this respect, and to trust to the cruets, when in their places, disguising whatever remains of the blemishes, after the foregoing treatment, rather than to endanger the solidity of the stand itself. By employing pieces of pumice of various sizes (keeping the flattened piece for plane surfaces), strips of emery-cloth folded over pieces of soft wood, Water-of-Ayr stone, and ordinary hand " buff -sticks " of various kinds, the "wires" of old cruet and liqueur frames may be rendered smooth enough for plating. "With perseverance, and the necessary labour, many old articles may be put into a condition for plating by hand labour with very creditable results ; and it may be some consolation to those living at a distance from large towns, if we tell them that during the first ten years of the electro -plating art, the numerous host of " small men " had no other means of preparing their work for plating than those we have men- tioned, many of whom have since become electro -depositors upon an extensive scale. Resilvering Electro-plate. This is quite a distinct class of ware from the preceding, inasmuch as the articles are manufactured from what is called white metal, in contradistinction to the basis of Sheffield plate, which, as we have said, is the red metal copper. The better class of electro -plate is manufactured from a good quality of the alloy known as German silver, which, approaching nearly to its whiteness, does not become very distinctly visible when the silver has worn from its surface. Inferior qualities of this alloy, however, are extensively used for the manufacture of cheap electro -plate, which is very little superior, as far as colour goes, to pale brass, while the latter alloy is also employed in the production of a still lower class of work. The comparatively soft alloy, of a greyish-white hue, called Britannia metal, is also extensively adopted as a base for electro -plate of a very showy and cheap description, of which enormous quantities enter the market, and adorn the shop -windows of our ironmongers and other dealers in cheap electro -plated goods. To determine whether an electro -plated article has been manufactured from a hard alloy, such as German silver, or from the soft alloy Britannia metal, it is only neces- OHAEACTEBISTICS OF ELECTRO -PLATE. 259 sary to strike the article with any hard substance, when a ringing, vibratory sound will be produced in the former case, while a dull, unmusical sound, with but little vibration, will be observed in the latter. Characteristics of Electro-Plate. Electro -plated articles of the best quality are invariably hard-soldered in all their parts ; the wires of cruet and liquor frames are attached by German silver nuts to the screwed uprights, or feet of the wires, instead of pewter solder, as in plated ware, and the bottoms of the stands are coated with silver, instead of being tinned, as in the former case. The mounts are of the same material as the rest of the article, and the handles and feet of cream-ewers and sugar-bowls are frequently of solid^ cast German silver. With these advantages the electro -plater should have little difficulty, if the articles have received fair treatment in use, in re- plating them and turning them out nearly equal to new, which it should be his endeavour to do. It sometimes occurs that ' ' ship plate ' ' that is, plated work which has been used on board ship when it reaches the hands of the electro -plater exhibits signs of very rough usage ; corner dishes are battered and full of indentations, while the flat surfaces of the insides are scored with cuts and scratches, sugges- tive of their having been frequently used as plates, instead of mere receptacles for vegetables ; the prongs of the forks, too, are frequently notched, cut, and bent to a deplorable extent. All these blemishes, however, must be removed by proper mechanical treatment, after the remaining silver has been removed by the stripping-bath. It is not unusual for those who contract for the replating of ship work 'to pay by the ounce for the silver deposited, in which case they will not allow the electro -plater to reap the full advantage of the old silver removed by stripping, but will demand an allowance in their favour, which, if too readily agreed to by an inexperienced plater, might greatly diminish his profit if the cost of buffing the articles happened to be unusually heavy ; he must, therefore, be upon his guard when undertaking work of this description for the first time, since, other- wise, he may suffer considerable loss, for which the present rate of payment for each ounce of silver deposited will not compensate. After stripping and rinsing, the articles require to be well polished, or buffed, and rendered as nearly equal to new work as possible ; they are then to be potashed, quicked, plated, and finished in the same way as new goods. Since there is now a vast quantity of nickel-plated work in the market, some of which is exceedingly white even for nickel, inexperienced or weak-sighted platers must be careful not to mistake such articles for silver-plated work. When in doubt, applying a single drop of nitric acid, which blackens silver while producing no imme- diate effect upon nickel, will soon set the mind at rest upon this point. 260 ELECTRO-DEPOSITION OF SILVER. Electro-tinned articles, which very much resemble silvered work, may also be detected in this way. We are tempted to make one other suggestion upon this subject, which may not be deemed out of place, it is this: a considerable quantity of nickel-plated German silver spoons and forks are entering the market, which, should they eventually fall into the hands of the electro -plater to be coated with silver, may cause him some trouble if he inadvertently treats them as German silver work, which in his haste he might possibly do, and attempts to render them smooth for plating by the ordinary methods of hand or lathe -buffing ; the extreme hardness of nickel even as compared with German silver will render his work not only laborious, but unne- cessary, for if he were aware of the true nature of the surface he would naturally remove the nickel by means of a stripping solution, and then treat the article as ordinary German silver work. The stripping solution for this purpose will be given when treating of nickel re-plating. It must be understood that in making suggestions of this nature, in passing, that they are intended for the guidance of those who may not have had the advantages of much practical expe- rience, of whom there are many in every art. Depositing Silver by Weight. In this country the silver deposit is frequently paid for by weight, the articles being carefully weighed both before and after being placed in the plater's hands. The price charged for depositing silver by the ounce was formerly as high as 143. 6d. ; at the present period, however, about 8s. per ounce only could be obtained, and in some cases even less has been charged. But unless dynamo -electricity be employed this would be about as profitable as giving ten shillings for half-a-sovereign. In France electro -plating is regulated by law, all manufacturers being required to weigh each article, when ready for plating, in the presence of a comptroller appointed by the Government, and to report the same article for weighing again after plating. In this way the comptroller knows to a fraction the amount of precious metal that has been added, and puts his mark upon tha wares accordingly, so that every purchaser may know at a glance what he is buying. In Birmingham there is a class of electro -depositors, called " electro -platers to the trade," who work exclusively for manufacturers of plated goods and others who, though platers, send a great portion of their work to the "trade" electro - platers, whose extensive and more complete arrangements enable them to deposit large quantities of the precious metals with consider- able economy and dispatch. In depositing silver at so much per ounce, the weighed articles, after being cleaned, quicked, and rinsed, are put into the bath, in which they are allowed to remain until the plater deems it advisable to re-weigh them, when they are removed from the bath, rinsed in DEPOSITING SILVER BY WEIGHT. 26 1 hot water, and placed in boxwood sawdust ; they are then lightly brushed over to remove any sawdust that may adhere to them, and carefully weighed. If still insufficiently coated the articles are again scratch-brushed, quicked, rinsed, and replaced in the bath ; the re- weighing and other operations being repeated as often as is necessary until the required deposit is obtained. This is a tedious and trouble- some method, and is sometimes substituted by the following : Suppose a certain number of spoons and forks have been weighed for the plating-bath, one of these articles is selected as a test sample, and is weighed separately ; being placed in the bath with the others, it is removed from time to time and re -weighed, to determine the amount of silver it has acquired in the bath. Thus if 24 dwts. of silver are required upon each dozen of spoons or forks, when the test sample has received about 2 dwts. of silver it is known that the rest have a like proportion, provided, of course, that each time it has been suspended in the bath the slinging wire and that part of the conduct- ing rod from which it was suspended were perfectly clean ; it is obvious, however, that even this method is open to a certain amount of doubt and uncertainty, if the workmen are otherwise than very careful. To render the operation of depositing by weight more certain and less troublesome, some electro -platers in France adopt what is termed a " plating balance." The articles are suspended from a frame connected to one end of the beam, and a scale pan, with its weights from the other end ; the balance, thus arranged, is placed in communi- cation with the negative electrode of the electric generator, and the anodes with the positive electrode. When the articles, as spoons and forks, for example, are suspended from the frame, and immersed in the bath, counter-balancing weights are placed in the scale-pan. A weight equivalent to the amount of silver to be deposited is then put into the pan, which, of course, throws the beam out of balance ; when the equilibrium becomes restored, by the weight of deposit upon the articles in solution, it is known that the operation is complete. The plater usually employs scales for each bath, especially when silvering spoons and forks. If preferred, the supporting frame may be circular, so that the soluble anode may be placed in the centre of the bath, and at equal distance from the articles. The centre anode need not prevent the employment of other anodes round the sides of the vessel, so that the articles receive the action of the current in front and behind them. A sounding bell may be so connected that it will indicate the precise moment when the equilibrium of the scale takes place. In working the silver baths for this purpose, the anode surface immersed in solu- tion is much greater than that of the articles. When the solution loses its activity additions of cyanide of silver are given to it, and when the cyanide is found to have become partially converted into 262 ELECTRO-DEPOSITION OF SILVER. carbonate of potassa, hydrocyanic acid is added, which combines with carbonate, and liberates carbonic acid gas. This method is preferred to that of adding fresh cyanide, since an accumulation of the car- bonated alkali retards the conductivity of the solution, as also does the hydrocyanic acid when added in excess. Roseleur's Argyrometric Scale. This is an automatic apparatus and is designed for obtaining deposits of silver ' ' without super- vision and with constant accuracy, and which spontaneously breaks the electric current when the operation is terminated. ' ' The apparatus is made in various sizes, suitable for small or large opera- tions ; Fig. 98 repre- sents the apparatus to be employed for the latter purposes. It consists of: I. A wooden vat, the upper ledge of which carries a brass winding rod, hav- ing 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 commu- nicate with cross brass rods by means of platinum wire hooks. These cross rods are flattened at their ends so that they may not roll, and at the same tune have a better contact with the "winding rod." 2. A cast-iron column screwed at its base to one of the sides of the bath, 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 being intended to maintain the beam and prevent the knives from leaving their bowls when the beam oscillates too greatly. In the middle of the two arms are two bowls of polished steel, hollowed out wedge-shaped, to receive the beam knives. One arm of the pillar has at its end a horizontal iron ring, in which is fixed a heavy glass tube which supports and insulates a polished iron cup to contain mercury ; beneath this cup is a small pad of india- Fig. 98. ARGYROMETRIC SCALE. 263 rubber, which, by means of a screw beneath, may be raised or lowered, by which means the mercury in the cup is levelled. A second lateral binding screw connects the negative electrode of the battery. 3. A cast-iron beam, carrying in its centre two sharp polished steel knives ; at each end are two parallel steel bowls, separated by a notch, intended for the knives of the scale pan and of the frame for supporting the articles. One arm of the beam is furnished with a stout platinum wire, placed immediately above and in the centre of the mercury cup, and as the beam oscillates it dips into, or passes out of, the cup. The scale pan is furnished with two cast- steel knives fixed to the metallic bar, which is connected to chains supporting the lower wooden box for the tare ; the smaller pan, for the weight representing the amount of silver to be deposited, is placed between these two. 4. The frame for supporting the work is also suspended by two steel knives, the vertical of which is of stout brass tubing, and is equal in size to the opening of the bath, and supports the rods to which the articles are suspended. The slinging wires are formed into a loop at one end for supporting the spoons or forks, and the vertical portion of each wire is covered with india-rubber tubing, to prevent it from receiving the silver deposit. In adjusting the apparatus, the pillar must be set perfectly upright by aid of a plumb line ; the clamps are then withdrawn from the forks, and the beam is carefully put in its place, care being taken to avoid injuring the knives that rest in the bowls in the centre of the pillar. The clamps are now replaced, and the beam should oscillate freely upon the knives without friction. The knives of the frame are next put in their places, as also those of the scale pan ; mercury is then poured into the six bowls, where the knives rest, until all the polished parts of the latter are covered. The insulated steel cup is then filled with mercury so high that the point of the platinum wire just touches it, when the beam is level ; the small elastic pocket is used for raising and lowering the mercury cup, so as to place it at the proper height for bringing the mercury in contact with the end of the platinum wire. When the articles have received the amount of silver corresponding to the weight in the pan at the opposite side of the beam, the equilibrium will be established, and the platinum wire will then leave the mercury, and thus break the circuit and stop the opera^ tion. By this automatic arrangement the operation needs no atten- tion, since the moment the platinum wire loses contact with the mercury electricity ceases to pass ; if, however, the articles are allowed to remain in the bath after they have received the proper amount of silver, a portion of this metal may be dissolved by the free cyanide in the solution, in which case the end of the platinum wire would again dip into the mercury and complete the circuit, when deposition would 264 ELECTRO-DEPOSITION OP SILVER. be renewed and continue until the increased weight of silver again caused the platinum wire to lose contact with the mercury. Solid Silver Deposits. Although it is possible to deposit silver, from a cyanide solution rich in metal (say eight ounces of silver per gallon), upon wax or gutta-percha moulds, this method is not practi- cally adopted. The usual method is to first obtain a copper electro- type mould or shell of the object in the ordinary way ; silver is then deposited within the mould (supposing it to be a hollow object) until of the required thickness ; the copper is afterwards dissolved from the silver either by boiling the article in hydrochloric acid, or, still better, a strong solution of perchloride of iron, either of which substances will dissolve the copper mould without in any way injuring the silver. The perchloride of iron for this purpose may be readily formed by dissolving peroxide of iron (commercial "crocus") in hot hydro- chloric acid. The method of dissolving the copper recommended by Napier, is as follows : " An iron solution is first made by dissolving a quantity of copperas in water ; heat this till it begins to boil ; a little nitric acid is then added nitrates of soda or potash will do ; the iron which is thus peroxidised may be precipitated either by ammonia or carbonate of soda ; the precipitate being washed, muriatic acid is added till the oxide of iron is dissolved. This forms the solution for dissolving the copper. When the solution becomes almost colourless, and has ceased to act on the copper, the article is removed, and the addition of a little ammonia will precipitate the iron along with a portion of the copper ; but after a short exposure the copper is redis- solved. The remaining precipitate is washed by decantation ; a little ammonia should be put into the two first waters used for washing. When washed, and the copper dissolved out, the precipitate is redis- solved in hydrochloric acid, and the silver article returned until the copper is all dissolved off. It is convenient to have two solutions of per- chloride of iron, so that while the iron in the one is being precipitated, the article is put into the other. The persalt of iron will be found to dissolve the copper more rapidly than muriatic acid alone ; persul- phate of iron must not be used, as it dissolves the silver along with the copper. " The silver article is now cleaned in the usual way, and heated to redness over a clear charcoal fire, which gives it the appearance of dead silver, in which state it may be kept, or, if desired, it may be scratched and burnished." A very simple and economical method of producing perchloride of iron is to reduce the native peroxide of iron, known as "redding," to a powder, and digest it in hot hydrochloric acid, by which the salt is obtained at a cost but little exceeding that of the acid employed, the native ore being worth only about 253. per ton, THICKNESS OF ELECTEO-DEPOSITED SILVER. 265 One great objection to solid electro-deposits of silver (and gold) is that the articles have not the metallic "ring," when struck with any hard substance, as silver ware of ordinary manufacture. "This disadvantage," says Napier, " is no doubt partly due to the crystalline character of the deposit, and partly to the pure character of the silver, in which state it has not the sound like standard or alloyed silver. That this latter cause is the principal one appears from the fact that a piece of silver thus deposited is not much improved in sound by being heated and hammered, which would destroy all crystallisation. v This is quite true, but when electron-deposited silver has been melted, and cast into an ingot, by which its crystalline character is completely destroyed, and which is only partially affected by simply annealing and hammering, the characteristic "ring" of the pure metal is re- stored. The absence of a musical ring in electro -deposited silver is not of much consequence, however, since this method of reproduction would only be applied to rare works of art, such as antique figures, and richly chased articles kept solely for ornament. On the Thickness of Electro -Deposited Silver. This may be considered a somewhat delicate theme to expatiate upon when we reflect that some articles of commerce, but more especially export goods and articles sold at mock auctions, frequently receive a coating of silver which not only defies measurement by the most delicate micrometer, but also renders estimation by any other means all but impossible. This class of work includes spoons and forks, cruet- frames, toast-racks, &c., manufactured from a very inferior descrip- tion of German silver or brass, while Britannia metal tea services, salt-cellars, and many other articles made from the same alloy enter the market in enormous quantities, with a mere blush of silver upon them, the thickness of which might be more readily estimated by imagination than by any practical test. As to the amount of silver which should be deposited upon articles of domestic use, to enable them to withstand ordinary wear and tear for a reasonable period, from i to 3 ounces per dozen for spoons and forks may be deposited. Taken as a guide, with the smaller quantity of silver upon them, such articles, with careful usage, should present a very creditable appear- ance after five years' use ; with the larger proportion, the articles should look well, though probably somewhat bare upon those parts most subject to friction, at the end of twenty years. The same arti- cles, if used in hotels or on board ship, would become unsightly in less than half the periods named, German silver tea and coffee services, to be fairly well plated or silvered, should not have less than 2 ounces of silver upon the four pieces, which may be distributed in about the following proportions : for a 5 -gill coffee-pot 12 dwts. ; 5 -gill teapot 12 dwts. ; sugar-basin 10 dwts. ; cream-ewer 6 dwts. 266 ELECTRO-DEPOSITION OF SILVER. When the same articles are required to be fully well plated, the pro- portions should be about as follows : For coffee and teapot, about i^ ounce of silver each ; sugar-basin I ounce, and cream-ewer about 10 to 15 dwts. The proportion of silver which should be deposited per square foot, for plating of good quality, is from i to i \ ounce. "With the latter proportion the electro -silvered work would nearly approach in quality the old Sheffield plate, and would last for a great number of years without becoming bare, even at the most prominent parts, unless the article were subjected to very severe treatment in use. Pyro-plating. It is well known that when a silver-gilt article as a watch-chain, for example has been broken, and afterwards repaired by hard soldering, that the film of gold almost entirely disappears from each side of the soldered spot, under the heat of the blow -pipe flame, to the extent of i or 2 inches on either side of the joining. The film of gold has, in fact, sunk into the body of the silver, as though it had become alloyed with this metal. By some persons this is really believed to be the case. We are, however, disposed to think that the absorption of the gold under these circumstances is due, not to an actual alloying of the two metals in the ordinary sense, but to the expansion of the silver by the heat, by which its molecular structure becomes disturbed, and the film of gold, being thus split up into infinitely minute particles, these become absorbed by the silver as the metal contracts on cooling, and consequently disappear from the sur- face. We hold this view because we do not think that the heat of the blowpipe flame required to fuse the solder would be sufficient to form an alloy in the proper sense; indeed, the heat required to "run" silver solder would not be sufficiently high even to " sweat " the silver of which the article is composed. The fact of a film of metal becom- ing absorbed by another metal under the influence of heat has been taken advantage of, and a process termed " pyro -plating " has been introduced, and has been worked to some extent in Birmingham. The process, which has been applied to coating articles of steel and iron more especially with gold, silver, platinum, aluminium, copper, &c., may be thus briefly described : The article is first steeped in a boiling solution of caustic potash ; it is then brushed over with emery - powder, and afterwards with a steel brush and a solution of common soda, in which it is allowed to remain for some time. It is next con- nected to the negative electrode of a strong battery, and immersed in a hot solution of caustic potash, abundance of hydrogen being evolved, and is allowed to remain until it has a " silvery " appearance. After rinsing, it is suspended in a silver bath, with a previously weighed metal plate of the same amount of surface placed as a cathode by its side ; this plate is taken out and weighed from time to time until sufficient WHITENING SILVER WORK. 267 silver has been deposited, -which indicates approximately the amount of deposit upon the article itself. The article is then removed and rinsed, and afterwards heated in a furnace until the silver is "driven" into the surface of the metal. If the steel article requires to be tem- pered, it is quenched in water, and then brought to the proper temper in the usual way. Whitening Electro-plated Articles. It is well known that articles which have been electro -plated tarnish more rapidly than silver goods ; and while this has by many persons been attributed to the extreme purity of the electro -deposited metal, which, it was. believed, was more susceptible of being attacked by sulphurous fumes and other impurities in the air, by others it is believed to be due to a small quantity of undecomposed salt remaining in the pores of the deposited metal, which undergoes decomposition, and causes the work to tarnish. In order to render electro -plate less liable to discolora- tion, the following method has been adopted, but, as will readily be seen, it could not be applied to all classes of work : The article is first dipped in a saturated solution of borax and then allowed to dry, when a thin layer of the salt remains upon the surface ; the article is then dipped a second or even a third time (drying after each dipping) until it is completely covered with a layer of borax. When large articles are to be treated this way, the borax may be applied with a soft brush. The article is next to be heated to a dull red heat, or until the borax fuses. When cold, it is to be put into a pickle of dilute sul- phuric acid, which rapidly dissolves the borax ; after rinsing in hot water it is placed in hot boxwood sawdust, and then treated in the usual way. "Whitening Silver Work. Articles of silver which in their original finished state were left either wholly or in part a dead white, and have lost this pleasing effect by wear or oxidation, may be restored to their original condition by the process termed whitening. The article is first brought to a dull red heat (not sufficient to melt the solder) over a charcoal fire if it be a brooch, watch-dial, or other small silver article, by means of the blowpipe flame, the article being placed on a large and flat piece of charcoal. When the piece of work has thus been heated uniformly all over, it is allowed to become cool, after which it is placed in a glazed earthenware vessel (an ordinary white basin will do), containing a sufficient quantity of very dilute sulphuric acid. In a short time the acid will dissolve the oxide from the surface, together with a small quantity of oxide of copper derived from the copper with which the silver was alloyed, and which, with the silver, becomes oxidised by the heat and subsequent action of the atmosphere. When the article is removed from the pickle in which it should remain for at least twenty minutes to half an hour if not of a suffi- 268 ELECTRO-DEPOSITION OF SILVER. ciently pure whiteness it may be heated and pickled again. "When the whitening is properly effected, the surface should present a beauti- ful pearl-white appearance, and be perfectly uniform in its lustrous dulness. Directly the article is removed from pickle, it should be rinsed in two separate waters, the last water (which should be distilled water, by preference) being boiling hot. The article, after being removed from the rinsing-bowl, should be allowed to dry spon- taneously, which it will do if the water is boiling hot. It is not a good plan, though it is frequently done, to put work which has been whitened in boxwood sawdust, since if it has been much used it is liable to produce stains. CHAPTER XX. IMITATION ANTIQUE SILVER. Oxidised Silver. Oxidising Silver. Oxidising with Solution of Platinum. Oxidising with Sulphide of Potassium. Oxidising with the Paste. Part-gilding and Oxidising. Dr. Eisner's Process. Satin Finish. Sul- phuring Silver. Niello, or Nielled Silver. Pink Tint upon Silver. Silvering Notes. Oxidised Silver. Soon after the art of electro -plating had become an established industry, the great capabilities of the "electro" pro- cess, as it was called, received the serious attention of the more gifted and artistic members of the trade, who, struck with the great beauty of electro -deposited silver, and the facilities which the process offered for the reproduction of antique works, induced some electro-platers of the time to make experiments upon certain classes of work with a view to imitate the effects seen upon old silver ; some of the results were highly creditable, and in a short time after "oxidised " silver became greatly in vogue, and has ever since been recognised as one of the artistic varieties of ornamental silver or electro -plated work. We scarcely think we shall err, however, if we venture to say that much, of the "oxidised " silver-plated work of the present time is far inferior in beauty and finish to that with which our shops and show-rooms were filled some thirty years ago. Indeed, when visiting the Paris Exhibition of 1878, we were much displeased with the very slovenly appearance of some of the plated goods which had been part- gilt and oxidised in the exhibits of some of the larger English and French firms. The specimens referred to had the appearance of having done duty as specimens in all the exhibitions since 1851, and had suffered by being repeatedly " cleaned up " for each occasion ; they were cer- tainly far from being creditable. " Oxidising " Silver. This term has been incorrectly applied, but universally adopted, to various methods of darkening the surface of silver in parts, by way of contrast to burnished or dead-white sur- faces of an article. Oxygen, however, has little to do with the discoloration, as will be seen by the following processes, which are employed to produce the desired effect. The materials used are various, and they are generally applied with a soft brush, a camel-hair brush 270 IMITATION ANTIQUE SILVER. being suitable for small surfaces. In applying either of the materials the article should be quite diy, otherwise it will spread over portions of the work required to be left white, and thus produce a patchy and inartistic effect. The blackening substances are generally applied to the hollow parts or groundwork of the object, while the parts which are in relief are left dead, or burnished according to taste. Oxidising with. Solution of Platinum. Dissolve a sufficient quantity of platinum in aqua regia, and carefully evaporate the result- ing solution (chloride of platinum) to dryness, in the same way as re- commended for chloride of gold. The dried mass may then be dissolved in alcohol, ether, or water, according to the effect which it is desired to produce, a slightly different effect being produced by each of the solutions. Apply the solution of platinum with a camel-hair brush, and repeat the operation as often as may be necessary to increase the depth of tone ; a single application is frequently sufficient. The ethereal or alcoholic solution of platinum must be kept in a well- stoppered bottle, and in a cool place. The aqueous solution of platinum should be applied while hot. Oxidising with Sulphide of Potassium. Liver of sulphur (sul- phide of potassium) is often used for producing black discoloration, erroneously termed oxidising. For this purpose four or five grains of the sulphide are dissolved in an ounce of hot water, and the solution applied with a brush, or the article wholly immersed if desired. The temperature of the solution should be about 150 Fahr. After a few moments the silver surface assumes a darkened appearance, which deepens in tone to a bluish -black by longer treatment. When the desired effect is produced the article is rinsed and then scratch-brushed, or burnished if required, or the blackened hollow surfaces are left dead according to taste. When it is desired to produce a dead surface upon an article which has been electro -silvered, the article may be placed in a sulphate of copper bath for a short time, to receive a slight coat- ing of copper, after which it is again coated with a thin film of silver in an ordinary cyanide bath. It has then the dead- white appearance of frosted silver. Where portions of the article are afterwards oxidised a very fine contrast of colour is produced. In using the sulphide of potassium solution it should be applied soon after being mixed, since it loses its activeness by keeping. Fresh solutions always give the most brilliant results. Since the sulphide dissolves the silver, it is necessary that it should be applied only to surfaces which have received a tolerably stout coating of this metal, otherwise the subjacent metal (brass, copper, or German silver) will be exposed after the sulphide solution has been applied. Oxidising with the Paste. For this purpose a thin paste is formed by mixing finely-powdered plumbago with spirit of turpentine, to OXIDISING PEOCfeSSES. 2*]! which mixture is sometimes added a small quantity of red ochre or jewellers' rouge, to imitate the warm tone sometimes observed in old silver articles. The paste is spread over the articles and allowed to dry, after which the article is brushed over with a long-haired soft brush, to remove all excess of the composition. The parts in relief are then cleaned by means of a piece of rag, or chamois leather, dipped in spirit of wine. This method of imitating old silver is specially applicable to vases, tankards, chandeliers, and statuettes. In case of failure in the manipulation, the dried paste may be readily removed by placing the article in a hot solution of caustic potash or cyanide, when, after rinsing and drying, the paste may be reapplied. To give the old silver appearance to small articles, such as buttons, for example, they are first passed through the above paste, and afterwards revolved in a barrel or " tumbler " containing dry sawdust, until the desired effect is produced. Fart-gilding and Oxidising. To give this varied effect to work, the articles are first gilt all over in the usual way ; certain parts are then stopped off, as it is termed, by applying a suitable varnish. When the varnish has become dry, the article is placed in the silvering bath until a sufficient coating, which may be slight, has been obtained. After rinsing, the object is immersed in a solution of sulphide of potassium until the required tone is given to the silvered parts, when the article is at once rinsed, carefully dried, and the protecting varnish dissolved off, when it is ready to be finished. Dr. Eisner's Process. A brownish tone is imparted to plated goods by applying to the surface a solution of sal-ammoniac, and a still finer tone by means of a solution composed of equal parts of sulphate of copper and sal-ammoniac in vinegar. To produce a fine black colour, Dr. Eisner recommends a warm solution of sulphide of potassium or sodium. Sulphide of Ammonium. This liquid may also be applied to the so- called oxidation of silver, either by brushing it over the parts to be oxidised, or by immersion. It may also be applied, with plumbago, by forming a thin paste with the two substances, which is afterwards brushed, or smeared over the surface to be coloured, and when dry a soft brush is applied to remove the excess of plumbago. If preferred, a little jewellers' rouge may be added to the mixture. Satin Finish. This process is thus described by Wahl : The sand- blast is in use in certain establishments to produce the peculiar dead, lustrous finish, known technically as satin finish, on plated goods ; a templet of some tough resistant material, like vulcanised india-rubber, is made of the proper design, and when placed over the article, pro- tects the parts which it is desired to leave bright from the depolishing action of the sand, while the only open portions of the templet are 272 IMITATION ANTIQUE SILVEE. exposed to the blast. The apparatus employed for this purpose con- sists of a wooden hopper, with a longitudinal slit below, through which a stream of fine sand is allowed to fall, by opening a sliding cover. Closely surrounding the base of the hopper is a rectangular trunk of wood, extending some distance below the base of the hop- per, and tapering towards the bottom, to concentrate the sand-jet. This trunk is closed about the sides of the hopper, and open below, and is designed to direct the stream of sand upon the surface of the article presented beneath its orifice. To increase the rapidity of the depolishing action of the sand, a current of air, under regulated pres- sure, is admitted into the upper part of the trunk, which, when the sand-valve is opened, propels it with more or less accelerated velocity upon the metallic surface below. For this purpose, either a " blower," or an air -compressor with accumulator, may be used ; and the pressure may be regulated at will. The sand is thus driven with more or less velocity down the trunk by the air-blast admitted above, and, falling upon the surface of the article presented at the bottom, rapidly v depolishes the exposed parts, while those protected by the templet are not affected. The articles are presented at the orifice of the trunk by the hands of the operator, which are suitably protected with gloves ; and as rapidly as the depolishing proceeds, he turns the article about till the work is done. The progress of the work is viewed through a glass window, set in a horizontal table, which surrounds the apparatus and which forms the top of a large box, into which the sand falls, and which is made tight to prevent the sand from flying about. A portion of this box in front, where the workman stands, is cut away, and over the opening is hung a canvas apron, which the operator pushes aside to introduce the work. The sand that accumulates in the box below is transferred again to the hopper, as required, and is used over and over again. The satin-finish produced by the sand-blast is exceed- ingly fine and perfectly uniform, and the work is done more rapidly than with the use of brushes in the usual way. Sulphuring Silver. A very fine blue colour, resembling " blued " steel, may be imparted to silver or plated surfaces, by exposing the article to the action of sulphur fumes. For this purpose, the article should be suspended in an air-tight wooden box ; a piece of slate or a flat tile is laid upon the bottom of the box, and upon this is placed an iron tray, containing a small quantity of red-hot charcoal or cinders ; about a teaspoonful of powdered sulphur is now quickly spread over the glowing embers, and the lid of the box immediately closed. After about a quarter of an hour, the lid may be raised (care being taken not to inhale the sulphur fumes) and the article promptly withdrawn ; if the article is not sufficiently and uniformly blued, it must be again suspended and a fresh supply of hot charcoal and NIELLO, OR NIELLED SILVER. 273 sulphur introduced. It is necessary that the articles to be treated in this way should be absolutely clean. Niello, or Nielled Silver. These terms* are applied to a process which is attributed to Maso Finniguerra, a Florentine engraver of the fifteenth century, and somewhat resembles enamelling. It consists, essentially, in inlaying engraved metal surfaces with a black enamel, being a sulphide of the same metal, by which very pleasing effects are produced. The " nielling " composition may be prepared by making a triple sulphide of silver, lead, and copper, and reducing the resulting compound to a fine powder. The composition is made as follows : A certain proportion of sulphur is introduced into a stoneware retort, or deep crucible. In a second crucible, a mixture of silver, lead, and copper is melted, and when sufficiently fused the alloy thus formed is added to the fused sulphur in the first vessel, which converts the metals into sulphides ; a small quantity of sal-ammoniac is then added, and the compound afterwards removed from the retort or cru- cible and reduced to a fine powder. The following proportions are given by Mr. Mackenzie : Put into the first crucible Flowers of sulphur 750 parts. Sal-ammoniac 75 Put into the second crucible Silver 15 parts. Copper . . , 40 Lead . ' . 80 When fused, the alloy is to be added to the contents of the first crucible. Roseleur recommends diminishing the proportion of lead, which impairs the blue shade of the nielling, and corrodes too deeply. To apply the powder, obtained as above, it is mixed with a small quantity of a solution of sal-ammoniac. After the silver work is en- graved, the operator covers the entire surf ace with the nielling compo- sition, and it is then placed in the muffle of an enamelling furnace, where it is left until the composition melts, by which it becomes firmly attached to the metal. The nielling is then removed from the parts in relief, without touching the engraved surfaces, which then present a very pleasing contrast, in deep black, to the white silver surfaces This process, however, is only applicable to engraved work. "Wahl describes a cheaper process of nielling, which consists "in engraving in relief a steel plate, which, applied to a sheet of silver, subjected to powerful pressure in a die, reproduces a faithful copy of the engraving. The silver sheet thus stamped is ready to receive the * The art was formerly called working in niello, T 274 IMITATION ANTIQUE SILVER. nielling. A large number of copies may be obtained from the same matrix. Such is the method by which a quantity of nielled articles are manufactured, as so-called Russian snuff-boxes, cases for spectacles, bon-bon boxes, &c. Roseleur suggests the following to produce effects similar to niel- ling : A pattern of the design, cut out of thin paper, such as lace paper, is dipped into a thin paste of nielling composition, or into a con- centrated solution of some sulphide, and then applied upon the plate of silver, which is afterwards heated in the muffle. The heat destroys the organic matter of the paper, and a design remains, formed by the composition which it absorbed. A solution of chloride of lime (bleaching powder) will blacken the surface of silver, as also will nitric acid. For all practical purposes, however, chloride of platinum and weak solutions of the sulphides before mentioned will be found to answer very well if applied with proper judgment. Fink Tint upon Silver. Fearn recommends the following for pro- ducing a fine pink colour upon silver : Dip the cleaned article for a few seconds in a strong hot solution of chloride of copper, then rinse and dry it, or dip it in spirit of wine and ignite the spirit. Silvering Notes. i. The anodes, if of rolled silver, should always be annealed before using them. This may easily be done by placing them over a clear charcoal, or even an ordinary clear fire, until they acquire a cherry-red heat : when cold, they are ready for use. If convenient to do so, it is a good plan to hard solder a short length of stout platinum wire (say about three inches long) to the centre of one edge of the anode, which may be united to the positive electrode of the battery, or other source of electricity, by a binding screw, or by pewter solder. The object of attaching the platinum wire is to enable the anode to be wholly immersed in the bath, and thus prevent it from being cut through at the water line, which is generally the case where anodes are only partially immersed. 2 . Worn Anodes. When the anodes have been long in use, their edges frequently become ragged, and if these irregularities are not removed fragments of the metal will fall into the bath, and, possibly, upon the work, causing a roughness of deposit. It is better, therefore, to trim the edges of anodes whenever they become thin and present a ragged appearance. 3. Precautions to be Observed when Filling the Bath with Work. Assum- ing the suspending rods to have been cleaned, the battery connections adjusted, and the preparation of the articles to be plated commenced, some means must be adopted to prevent the articles first put into the bath from receiving too quick a deposit while others are being got ready. In the first instance, the full force of the current must be SILVEEING NOTES. 275 checked, which may be done by exposing a small surface of anode in solution or suspending a plate of brass or a small silver anode as a "stop," or check, to the negative rod, until a sufficient number of articles (say spoons or forks, for example) have been suspended, when the stop may be removed and the remainder of the articles immersed until the conducting rod is full ; the rest of the suspending rods should then be treated in tho same way. When magneto or dynamo- electric machines are employed, the full strength of the current is checked by the employment of the resistance coil, a description of which is given in Chapter XXXVI. A simple way of diminishing the amount of current, when filling the bath with work, is to inter- pose a thin iron wire between the positive electrode and the sus- pending rod, which must be removed, however, when the cathode surface (the articles to be plated) in the bath approaches that of the anode surface. 4. Plating Different Metals at the Same Time. It is not good practice to place articles composed of different metals or alloys indiscriminately in the bath, since they do not all receive the deposit with equal facility. For example, if two articles, one copper or brass, and another Britannia metal or pewter, be immersed in the solution simultaneously, the former will at once receive the deposit of silver, while the latter will scarcely become coated at all, except at the extremities. Since the best conductor receives the deposit most freely, the worst conductor (Britannia metal, pewter, or lead) should first be allowed to become completely coated, after which copper or brass articles may be intro- duced. It is better, however, if possible, to treat the inferior con- ductors separately than to run the risk of a defective deposit. 5. Excess of Cyanide. When there is a large excess of cyanide in the plating bath, the silver is very liable to strip, or peel off the work when either scratch-brushed or burnished ; besides this, the anodes become dissolved with greater rapidity than is required to merely keep up the proper strength of the bath, consequently the solution becomes richer in metal than when first prepared. The depositor must not confound the terms "free cyanide" with "excess" of cyanide : the former refers to a small quantity of cyanide beyond that which is necessary to convert into solution the precipitate thrown down from the nitrate, which is added to the solution to act upon and dissolve the anode while deposition is going on ; the latter term may properly be applied to any quantity of cyanide which is in excess of that which is necessary for the latter purpose. In preparing plating solutions from the double cyanide of silver and potassium, great care must be taken, when precipitating the silver from its nitrate solution, not to add the cyanide in excess, other- wise a portion of the precipitated cyanide of silver will be re-dissolved, 276 IMITATION ANTIQUE SILVER and probably lost when decanting the supernatant liquor from the precipitate. When the precipitation is nearly complete, the last additions of cyanide solution should be made very cautiously, and only so long as a turbidity, or milkiness, is produced in the clear liquor above the precipitate. Instances have been known in which not only silver, but gold precipitates also, have been partially re- dissolved by excess of cyanide and the solutions thrown away by ignorant operators as waste liquors. If by accident an excess of cyanide has been used during the precipitation of gold or silver solutions, the difficulty may be overcome by gradually adding a solu- tion of the metallic salt until, in its turn, it ceases to produce turbidity in the clear supernatant liquor. Again, in dissolving precipitates of silver or gold, care is necessary to avoid using a large excess of cyanide ; a moderate excess only is necessary. 6. Articles Falling into the Bath. When an article falls into the bath, from the breaking of the slinging wire or otherwise, its recovery generally causes the sediment which accumulates at the bottom of the vat to become disturbed, and this, settling upon the work, produces roughness which is very troublesome to remove. If not immediately required, it is better to let the fallen article remain until the rest of the work is plated ; or if its recovery is of immediate importance, the rod containing the suspended articles should be raised every now and then during about half an hour, in order to wash away any sediment that may have settled on the work. By gently lifting the rod up and down, or raising each piece separately, the light particles of sediment may readily be cleared from the surface of the work. When very large articles, as salvers, for example, are immersed in the bath, they should be lowered very gently, so as not to disturb the sediment referred to ; if this precaution be not rigidly followed, especially if the vat be not a very deep one, the lower portion will assuredly become rough in the plating, which the most skilful burnishing will be incapable of removing. We have frequently known it to be neces- sary to strip and replate articles of this description from the cause referred to. It must also be borne in mind that when anodes become very much worn minute particles of silver fall to the bottom of the vessel, which, when disturbed in the manner indicated, rise upward, settle upon the work, and become attached, by what may be termed electro- soldering, to the work, causing the deposit to be rough, and when such surface is afterwards smoothed by polishing, the part exhibits numerous depressions, or is "pitted," as the Sheffield burnishers term it. 7. Gleaning Suspending Rods. It is a very common practice with care- less workmen to clean the suspending rods with emery cloth while they are in their places across the sides or ends of the plating- vat. SILVERING NOTES. 277 This is a practice which should be strictly disallowed, for it is evident that the particles of brass, emery, and metallic oxides which become dislodged by the rubbing process, must enter the solution, and being many of them exceedingly light, will remain suspended in the solution for a considerable time, and finally deposit upon the articles when placed in the vat, while some portions of the dislodged matter will become dissolved in the bath. All suspending rods should be cleaned at some distance from the plating vat, and wiped with a clean dry rag after being rubbed with emery cloth before being replaced across the tank. 8. Electro-silvering Pewter Solder. Besides the methods recommended elsewhere, the following may be adopted : After thoroughly cleaning the article, apply to the soldered spot with a camel-hair brush a weak solution of cyanide of mercury ; or if it be a large surface the soldered part must be dipped for a short time in the mercury solution. In either case the article must be well rinsed before being immersed in the silver bath. 9. Metal Tanks. When working solutions in iron tanks, the plater should be very careful not to allow the anodes, or the work to be coated, to come in contact with the metallic vessel while deposition is taking place, since this will not only cause the current to be diverted from its proper course, but will also cause the anodes, especially if there be a large excess of free cyanide in the bath, to become eaten into holes, and fragments of the metal will be dislodged and fall to the bottom of the vat, and possibly small particles of the metal will settle upon the work. We remember an instance in which several wooden nickel-plating tanks, lined with stout sheet lead, coated with pitch, yielded very poor results from some cause unknown to the plater. Having been consulted on the matter, the author soon discovered the source of mischief : the copper hooks supporting the heavy anodes had become imbedded in the pitch, and were in direct communication with the lead lining, from which a greater portion of the pitch had scaled off, leaving the bare metal exposed below the surface of the solution. Upon applying a copper wire connected to the negative electrode of the large Wollaston battery, at that time used at the establishment, to the leaden flange of each tank the author obtained bril- liant sparks, to the great astonishment of the plater and his assistants, and subsequently caused strips of wood to be placed between the side anodes and the lead lining, after which nickel-plating proceeded with- out check. 10. Bright Plating. Even in the most skilful hands the bright solu- tion is very liable to yield ununiform results. When the solution has remained for some time without being used it is apt to give patchy results, the work being bright in some parts only ; if the solution is 2y3 IMITATION ANTIQUE SILVER. disturbed, by taking out work or by putting in fresh work, sometimes the latter will refuse to become bright, and the remainder of the work in the bath will gradually become dull. To obviate this the bath should be well stirred over night, and all the work to be plated at one time put into the bath as speedily as possible, and all chances of disturbance avoided. When the work is known to have a sufficient coating of the bright deposit, the battery connection should be broken and the articles then at once removed from the bath. On no account must an excess of the "bright " liquid be allowed to enter a bath. 1 1 . Dirty Anodes. When the anodes, which should have a greyish appearance while deposition is taking place, have a pale greenish film upon their surface, this indicates that there is too little free cyanide in the bath, or that the current is feeble ; the battery should first be attended to, and if found in good working order, and all the connec- tions perfect, an addition of cyanide should be made ; this, however, should only be done the last thing in the evening, the bath then well stirred and left to rest until the following morning. 12. Dust on the Surface of the Bath. Sometimes in very windy weather the surface of the bath, after lying at rest all night, will be covered with a film of dust ; to remove this spread sheets of tissue paper, one at a time, over the surface of the liquid, then take the sheets up one by one and place them in an earthen vessel ; the small amount of solution which they have absorbed may be squeezed from the sheets, passed through a filter, and returned to the bath, and the pellets of paper may then be thrown amongst waste, to be afterwards treated for the recovery of its metal. 13. Old Slinging Wires. It is not a good plan to use a slinging wire, one end of which has received a coating of silver or other metal more than once, without first stripping off the deposited metal , in the first place the coated end of the wire becomes very brittle, and is liable to break when twisting it a second time, possibly causing the article to fall into the bath, or on a floor bespattered with globules of mercury and other objectionable matter ; again, the broken fragments of silver- covered wire, if allowed to fall carelessly on the floor, get swept up with the dirt, and the silver thus wasted. The wires which have been used once should be laid aside, with the plated ends together, and at a convenient time these ends should be dipped in hot stripping solution, until all the silver is dissolved off, and after rinsing, the ends should be made red hot, to anneal them ; the wires may then be cleaned with emery cloth and put in their proper place to be used again. These minor details should always be attended to, since they do not neces- sarily involve much time and are assuredly advantageous from an economical view. It is too commonly the practice with careless opera- tors to neglect such simple details, but the consequence is that their SILVERING NOTES. 279 plating operations are often rendered unnecessarily troublesome, while their workshops are as unnecessarily untidy. 14. Battery Connections, Before preparing work for the bath, the binding screws, clamps, or other battery connections should be ex- amined, and such orifices or parts as form direct metallic communication between the elements of the battery and the anodes and cathodes should be well cleaned if they have any appearance of being oxidised or in any way foul. The apertures of ordinary binding screws may be cleaned with a small rat-tail file, and the flat surfaces of clamps rubbed with emery cloth laid over a flat file. When binding screws, from long use or careless usage, become very foul, they should be dipped in dipping acid, rinsed, and dried quickly. Previous to put- ting work in the bath, a copper wire should be placed in contact with the suspending rod and the opposite end allowed to touch the anode, when the character of the spark will show if the current is sufficiently vigorous for the work it has to do ; if the spark is feeble, the connec- tions should be looked to, and the binding screws tightened, if neces- sary ; the hooks and rods supporting the anodes should also be examined, and if dirty, must be well cleaned, so as to insure perfect contact between the metal surfaces. 15. Gutta-percha Lining for Plating Tanks. This material should never be used for lining the insides of tanks which are to contain cyanide solutions, since the cyanide has a solvent action upon it, which, after a time, renders the solution a very bad conductor. The author once had to precipitate the silver from an old cyanide solution which had remained for a long period in a gutta-percha lined bath, and soon after the acid (sulphuric) had been applied to throw down the silver, there appeared, floating upon the surface of the liquid, numerous clots of a brown colour, which proved to be gutta-percha, although greatly altered from its original state. CHAPTER XXI. ELECTRO-DEPOSITION OF NICKEL. Application of Nickel-plating. The Depositing Tank. Conducting Rods. Preparation of the Nickel Solution. Nickel Anodes. Nickel-plating by Battery. The Twin-Carbon Battery. Observations on Preparing Work for Nickel-plating. The Potash Bath. Dips or Steeps. Dipping Acid. Pickling Bath. Application of Nickel-plating. When applied to purposes for which it is specially adapted, nickel-plating may be considered one of the most important branches of the art of electro -deposition. In the earlier dayB of nickel-plating too much was promised and expected from its application, and, as a natural consequence, frequent disap- pointments resulted from its being applied to purposes for which it was in no way suited. For example, it was sometimes adopted as a substitute for silver-plating in the coating of mugs or tankards used as drinking vessels for malt liquors, but it was soon discovered that those beverages produced stains or discolorations upon the polished nickel surface, which were not easily removed by ordinary means, owing to the extreme hardness of the metal as compared with silver or plated goods. Again, nickel-plated vegetable -dishes became stained by the liquor associated with boiled cabbage or spinach, rendering the articles unsightly, unless promptly washed after using a precau- tionary measure but seldom adopted in the best-regulated sculleries. It was also found that polished nickel -plated articles when exposed to damp assumed a peculiar dulness, which after a time entirely destroyed their brilliant lustre, whereas in a warm and dry situation they would remain unchanged for years, a fact which the mullers of our restaurants and taverns which were nickel -plated many years ago bear ample testimony at the present day. While practical experience has taught us what to avoid in connec- tion with nickel-plating, it has also shown how vast is the field of usefulness to which the art is applicable, and that as a protective and ornamental coating for certain metallic surfaces, nickel has at present no rival. Its great hardness which closely approximates that of steel renders its surface, when polished, but little liable to injury from ordinary careless usage ; while, being a non-oxidisable metal, it retains its natural whiteness, even in a vitiated atmosphere. THE DEPOSITING VAT. 28l The metals ordinarily coated with nickel by electro -deposition are copper, brass, steel, and iron, and since these require different pre- paratory treatment, as also different periods of immersion in the nickel bath, they will be treated separately. The softer metals, as lead, tin, and Britannia metal, are not suited for nickel-plating 1 , and should never be allowed to enter the nickel bath. Tlie Depositing Vat, or Tank. The depositing vessel may be made from slate or wood, but the following method of constructing a vat is that most generally adopted, and when properly carried out produces a vessel of great permanency. The tank is made from 2|-incJi deal, planed on both sides, the boards forming the sides, ends, and bottom being grooved and tongued, so as to make the joints, when put R _________ !l __^^ together, water-tight ; they are held together by long bolts, tapped at one end to receive a nut. The sides and ends, as also the bottom, are likewise secured in their position by means of screw-bolts, as seen in Fig. 99. When the tank is Fi - 99- well screwed together, as in the engraving, the interior is to be well lined with pure thin sheet lead. It is of great importance that the lead used for this purpose be as pure as possible, for if it contain zinc or tin it will be liable to be acted upon by the nickel solution which it is destined to hold, and pin-holes will be formed, through which the solution will eventually escape. The joints of the leaden lining must not be united by means of solder, but by the autogenous process, or " burning," as it is called, that is, its seams are fused together by the hydrogen flame an operation with which intel- ligent plumbers are well acquainted. If solder were used for this purpose voltaic action would soon be set up between the lead and the tin of the solder by the action of the nickel solution, and in time a series of holes would be formed, followed by leakage of the vat. When the lead lining is complete the vessel must be lined throughout with matched boarding, kept in its position by a rim of wood fastened round the upper edge of the tank. These tanks are usually 3 feet wide, 3 feet deep, and about 6 feet long, and hold about 250 gallons. Before using the tank it should be well rinsed with clean water. It is a good plan to quite fill the tank with water, and allow it to remain therein for several hours, by which time the pressure of the liquid will soon indicate if there be a leakage at any part ; it should then be emptied and examined, to ascertain if thoroughly water-tight. 282 ELECTRO-DEPOSITION OF NICKEL. "We will assume that it is desired to make up 100 gallons of nickel solution in which case the depositing tank should be capable of holding not less than 120 gallons, to allow for the displacement of liquid by the anodes and articles to be immersed, as also to allow sufficient space say 3 inches above the solution to prevent the liquid from reaching the hooks by which the anodes are suspended, when the bath is full of work. Although we have taken 100 gallons of solution as a standard, we may state that, for large operations, tanks capable of holding 250 up to 500 gallons, or even more, are commonly employed. Conducting Rods. These rods, which are used for supporting the nickel anodes, as also the articles to be nickeled, generally consist of I -inch brass tubing, with a core of iron rod ; they are commonly laid across the bath, lengthwise, extending about 3 inches beyond the extreme ends of the vessel. Sometimes, however, shorter rods are employed, and these are laid across the bath from side to side. For a nickel bath of 100 gallons and upwards three such suspending rods are used, one rod being laid from end to end, close to each side of the tank, upon which the requisite number of anodes are suspended by their hooks ; a third rod is laid, also longitudinally, along the centre of the tank, midway between the other two, for suspending the articles to be nickeled ; the anode rods are to be con- nected together by a stout copper wire at one end by soldering. These rods are termed respectively the posi- tive and negative conducting rods, the former receiving the anodes, and the latter the work to be nickeled. Fig. 100 represents a cast nickel anode and its supporting hook of stout copper wire, which latter should not be less than inch in thickness. In order to insure a perfect connection Fi S- I00 ' between the copper hook and the anode, the author has found it very advantageous to unite the two by means of pewter solder, in the following way,* and which it may be useful to quote here: The holes " Electro-Metallurgy Practically Treated." By Alexander Watt. PBEPAEATION OF NICKEL SOLUTIONS. 283 being cleaned with a rat-tail file, the hooks were dipped into ordinary- dipping acid (sulphuric and nitric acid) for one instant, and rinsed. One end of each hook was then moistened with chloride of zinc, and immediately plunged into a ladle containing molten tin or pewter solder. The tinned hook was next inserted into the hole in the anode, and a gentle tap with a hammer fixed it in its place. The anode being laid flat on a bench, with a pad of greased rag beneath the hole, the next thing to do was to pour the molten solder steadily into the hole, and afterwards to apply a heated soldering iron. It is better, however, before pouring in the solder, to heat the end of the anode, so as to prevent it from chilling the metal, and a little chloride of zinc solution should be brushed over the inner surface of the aperture, so as to induce the solder to "run" well over it, and thus insure a perfect connection between the hook and the anode. The importance of securing an absolutely perfect connection between these two surfaces will be recognised when we state that we have known instances in which more than half the number of anodes, in a bath holding 250 gallons, were found to be quite free from direct contact with the supporting hooks, owing to the crystallisation of the nickel salt within the interior of the perforation having caused a perfect separation of the hooks from their anodes. It was to remedy this defect that the author first adopted the system of soldering the con- nections. Preparation of the Nickel Solution. The substance usually employed is the double sulphate of nickel and ammonia (or ''nickel salts," as they are commonly called), a crystalline salt of a beautiful emerald green colour. This article should be pure. For 100 gallons of solution the proportions employed are : Double sulphate of nickel and ammonia . . 75 Ibs. Water .;...'*... 100 gallons. Place the nickel salts in a clean wooden tub or bucket, and pour upon them a quantity of hot or boiling water ; now stir briskly with a wooden stick for a few minutes, after which the green solution may be poured into the tank, and a fresh supply of hot water added to the undissolved crystals, with stirring, as before. This operation is to be continued until all the crystals are dissolved, and the solution trans- ferred to the tank. A sufficient quantity of cold water is now to be added to make up 100 gallons in all. Sometimes particles of wood or other floating impurities occur in the nickel salts of commerce ; it is better, therefore, to pass the hot solution through a strainer before it enters the tank. This may readily be done by tying four strips of wood together in the form of a frame, about a foot square, over which a piece of unbleached calico must be stretched, and secured either by 284 ELECTKO-DEPOSITION OF NICKEL. means of tacks or by simply tying it to each corner of the frame with string. Nickel Anodes. It is not only necessary that the nickel salts should be perfectly pure which can only be relied upon by purchas- ing them at some well-known, respectable establishment but it is equally important that the nickel plates to be used as anodes which may be either of cast or rolled nickel should be of the best quality. A few years ago there was no choice in this matter, for rolled nickel was not then obtainable. Now, however, this form of nickel can be procured of almost any dimensions, of excellent quality, and any degree of thinness, whereby a great saving may be effected in the first cost of a nickel-plating outfit. Again, some years ago it was im- possible to obtain cast nickel anodes of moderate thickness, conse- quently the outlay for this item alone was considerable. Such anodes can now be procured, however, and thus the cost of a nickel-plating plant is greatly reduced, even if cast anodes are adopted instead of rolled nickel. Nickel-plating by Battery. For working a loo-gallon bath, four cells of a 3 -gallon Bunsen battery will be required, but only two of these should be connected to the conducting rods until the bath is about half full of work, when the other cells may be connected, which should be done by uniting them for intensity; that is, the wire attached to the carbon of one cell must be connected to the zinc of the next cell, and so on, the two terminal wires being connected to the positive and negative conducting rods. If preferred, however, the batteries may be united in series, as above, before filling the bath with work, in which case, to prevent the articles first placed in the solution from "burning," as it is termed owing to the excess of electric power it will be advisable to suspend one of the anodes temporarily upon the end of the negative rod farthest from the battery, until the bath is about half filled with work, when the anode may be removed, and the remainder of the articles suspended in the solution. In working larger arrangements with powerful currents to which we shall here- after refer resistance coils are employed, which keep back the force of the electric current while the bath is being supplied with work, and even when such coils are used it is usual to suspend an anode or some other " stop," as it is called, from the negative rod during the time the work is being put into the solution. Twin-Carbon Battery. A very useful modification of the Bunsen battery, and well suited for nickel-plating upon a small scale, is the American twin- carbon battery, introduced by Condit, Hanson and Van Winkle, of New Jersey, U.S.A., which, in its dissected condition, is represented in Fig. TOI. A pair of carbon plates are united by a clamp, with binding screw attached, as shown in Fig. i . A plate TWIN-CAKBON BATTERY. of stout sheet zinc is cut out so as to leave a projecting piece, to which a binding screw is also connected, as at 2, and the zinc is turned up into an oval form to admit the porous cell, 4. The zinc being put into the outer cell, 3 (which is made of stoneware), the porous cell is Fig. 10 1. placed within the zinc cylinder, and the twin carbons then deposited in the porous cell. The exciting fluids are, for the zinc, which must of course be well amalgamated, I part oil of vitriol to 12 parts water. The porous cell is filled to the same height with a mixture composed of equal measures of oil of vitriol and water, to which 2 ounces of nitric acid are added. This is an exceedingly useful and compact battery, and is specially serviceable in nickel-plating upon a moderate scale. When great electro -motive force is required, strong nitric acid is used instead of the above mixture in the porous cell. Observations on Preparing the Work for Nickel-plating. For several reasons, it is of greater importance that the articles to be coated with nickel should be what is termed chemically clean, than in any other branch of electro-deposition. The excess of cyanide used in gilding, silvering, and brassing solutions is capable of dissolving from the work such slight traces of organic matter as might be accidentally communicated by the hands, and being a powerful solvent of metallic oxides, the delicate film of oxide which quickly forms upon the surface of recently scoured work becomes at once dissolved in a cyanide solu- tion. In the case of a nickel solution, however, which is prepared from a neutral salt, no such solvent action would take place, and the slightest trace of organic matter or of oxide resulting from the action of the air upon the prepared article, would prevent the adhesion of the nickel to the underlying metal, and the work would consequently strip. In some establishments, to prevent the possibility of direct contact of the hands with the work while being scoured, the men are required to hold the work with a clean piece of rag, which is frequently dipped in water during the operation of scouring ; a good substitute for this is to keep the hand holding the work, while 286 ELECTRO-DEPOSITION OP NICKEL. brushing it with powdered pumice or other material, well charged with the substance by dipping the fingers occasionally in the powder. Before explaining the operation of scouring, it will be necessary to describe the various solutions, or "dips," as they are termed, in which the articles are immersed before and after being scoured. The first and most important of these is the potash bath, in which all articles to be nickel-plated are immersed before undergoing any other treatment. The Potash Bath. The vessel in which the solution of potash is kept for use generally consists of a galvanised wrought -iron tank capable of holding from 20 to 150 gallons, according to the require- ments of the establishment. An iron pipe, or worm, is placed at the bottom of the tank, one end of which communicates with a steam boiler, a stopcock being connected at a convenient distance for turn- ing the steam on or off ; or the tank may be heated by gas jets, by Fig. 102. means of perforated piping fixed beneath it. An ordinary form of potash tank is shown at A in Fig. 102, in which the worm-pipe is indicated by the dotted lines, &c., a , the vertical pipe b, with its stopcock c, being conveniently placed at one corner of the tank, as shown in the engraving. The waste steam from the worm-pipe escapes into a second tank B, partly filled with water, which thus becomes heated, and is used for rinsing. A rod of iron, or brass tube with an iron core, rests upon the bath, longitudinally, for suspending the articles in the caustic liquor. The potash solution is made by dissolving half a pound of American potash in each gallon of water required to make up the bath, and the solution is always used hot. The object of immersing the work to be nickeled in the potash bath, is to render soluble any greasy matter which may be present, as, for example, the oil used in the various processes of polishing. In a freshly made solution (which must DIPS, OB STEEPS. 287 always be kept hot), the work will only require to be immersed for a few minutes, by which time the greasy matter will have become con- verted into soap, and being thus rendered soluble, may easily be removed by the subsequent operations of brushing with pumice, &c. ; but we must bear in mind that the causticity of the solution (and consequently its active property) gradually becomes diminished, not only in consequence of the potash having combined with the greasy matter, but also owing to its constantly absorbing carbonic acid from the air. When the bath has been some time in use, therefore, it will be necessary to add a fresh quantity of potash, say about a quarter of a pound to each gallon. It is easy to ascertain if the potash has lost its caustic property by dipping the tip of the finger in the solu- tion, and applying it to the tongue. As the bath becomes weakened by use, the articles will require a longer immersion, and, with few exceptions, a protracted stay in the bath will produce no injurious effect. Articles made from Britannia metal, or which have pewter solder joints, should never be suffered to remain in the potash bath longer than a few minutes, since this alkali (caustic potash) has the power of dissolving tin, which is the chief ingredient of both. Again, articles made from brass or copper should never be suspended from the same rod as steel and iron articles, in case the potash solution should have become impregnated with tin dissolved from solder, &c. ; for if this precaution be not observed it is quite likely (as we have frequently seen in an old bath) that the steel articles will become coated with tin, owing to voltaic action set up in the two opposite metals by the potash solution. Cast-iron work, in which oil has been used in the finishing, should, owing to its porous character, be immersed in the potash bath for a longer period than other metals in order to thoroughly cleanse it from greasy matter. Dips, or Steeps. Besides the potash solution/certain other liquids are employed in nickel-plating after the work has been " potashed " and scoured, which may be properly described in this place ; and we may here remind the reader that the employment of these dips, as they are called, is based upon the fact that the neutral solution of nickel has no power (unlike cyanide solutions) of dissolving even slight films of oxide from work which, after being scoured, has been exposed to the air and become slightly oxidised on the surface. In order, therefore, to remove the faintest trace of oxidation from the surface of the work the presence of which would prevent the nickel from adhering it is usual to plunge it for a moment in one or other of the following mixtures after it has been scoured, then to rinse it, and immediately suspend it in the nickel bath. The Cyanide Dip. This solution is formed by dissolving about half a pound commercial cyanide of potassium in each gallon of water ; for 288 ELECTRO-DEPOSITION OF NICKEL. operations on a moderate scale, a stoneware vessel capable of holding about fifteen gallons may be supplied with about twelve gallons of the solution. Baths of the form shown in A, Fig. 103, and which are to be obtained at the Lambeth potteries, are well suited to this purpose. Another form of stoneware vessel is seen in Fig. 104, which, being Fig. 103. Fig. 104. deeper, is useful for certain classes of work. In applying the cyanide dip to articles of great length, it is commonly the practice to employ a common earthenware jug, kept near the dipping bath ; this, being filled with the cyanide solution, is held above the highest point of the article (a brass tube, for instance) and tilted so that its contents may flow downward and pass all over the tube, which is then quickly taken to the water trough or tray and well rinsed, when it is at once placed in the nickel bath. On using the cyanide dip, it must be remembered that its only object is to dissolve from the surface of the recently scoured work an almost imaginary film of oxide , therefore the mere contact of the cyanide solution is amply sufficient to accomplish the object ; on no account should brass or copper articles be exposed to the action of the dip for more than a few seconds ; indeed, if the solution is in an active condition, the quicker the operation is con- ducted the better. It will readily be understood, however, that the weak cyanide bath will gradually lose its activity, when the dipping may be effected somewhat more leisurely. It is a common fault, however, to use these dips long after they have yielded up their active power, and we have frequently known them to be employed, and relied upon, when they were utterly useless. The Acid Dip. This solution, which is used for dipping steel and iron articles after they have been scoured, is composed of hydrochloric (muriatic) acid and water, in the proportion of half a pound of the acid to each gallon of water. The solution is generally contained in a shallow wooden tub, which may conveniently be the half of a brandy cask or rum puncheon ; but since the acid eventually finds its way to the iron hoops by which such vessels are held together, it is a good DIPPING ACID. 289 plan, in the first instance, to have a couple of wooden hoops, secured by copper rivets, placed over the vessel so as to prevent it from leak- ing in the event of the iron hoops giving way in consequence of the corrosive action of the acid liquor. Precautions of this nature will prevent leakage and the inconvenience which it involves. Dipping Acid. This name is given to a mixture which is frequently used for imparting a bright surface to brass work, and which is variously composed according to the object to be attained. When required for dipping brass work preparatory to nickel-plating, it is commonly composed of Sulphuric acid . . . . . .4 Ibs. Nitric acid . . . . . . . . 2 Water 4 pints. In making up the above mixture, the nitric acid is first added to the water, and the sulphuric acid (ordinary oil of vitriol) is then to be gradually poured in, and the mixture stirred with a glass rod. When cold, it is ready for use. The mixture should be made, and kept, in a stoneware vessel, which should be covered by a sheet of stout glass each time after using, to prevent its fumes from causing annoyance and from injuring brass work within its vicinity. The "dipping" should always be conducted either in an outer yard, or near a fire- place, so that the fumes evolved during the operation may escape, since they are exceedingly irritating when inhaled by the lungs. When it is convenient to do so, it is a good plan to have a hood of wrought iron, painted or varnished on both sides, fixed above an ordinary fireplace in the workshop, and to have a hole made in the brickwork above the mantelpiece to conduct the fumes into the chim- ney ; this arrangement, however, will be of little use, unless there is a good draught in the chimney. It is well to ascertain this, there- fore, before the dipping is proceeded with, which may be readily done by holding a large piece of ignited paper above the grate, when, if the flame persistently inclines towards the chimney, the draught may be considered perfect ; if, however, it shows any inclination to come forward, it may be assumed that the draught is imperfect, owing to the chimney being filled with cold air. In this case lighted paper should be applied as before, until the flame and smoke of the ignited material have a direct tendency upward, or in the direction of the chimney. We are induced to give these precautionary hints more especially for the guidance of those who may be necessitated to work in apartments of limited space. In all cases, a vessel of clean water should be placed close to the dipping bath, into which the articles are plunged the instant after they have been removed irom the dipping acid. 2 9 6 ELECTRO-DEPOSITION OF NICKEL. Pickling Bath. Cast iron, before being nickeled, requires to be placed in a cold acid solution, or pickle, as it is called, to dissolve or loosen the oxide from its surface. The pickle may be prepared in a wooden tub or tank, from either of the following formulae : Sulphuric acid (oil of vitriol) . . . . J lb. Water i gallon. Cast-iron work immersed in this bath for twenty minutes to half an hour will generally have its coating of oxide sufficiently loosened to be easily removed by means of a stiff brush, sand, and water. When it is desired that the articles should come out of the bath bright, instead of the dull black colour which they present when pickled in the plain sulphuric acid bath, the following formula may be adopted : Sulphuric acid . . . . . . . i Ib. Water . . . . ; . ;: . ' . i gallon. Dissolve in the above two ounces of zinc, which may be conveniently applied in its granulated form. When dissolved, add half a pound of nitric acid, and mix well. CHAPTER XXII. ELECTRO -DEPOSITION OF NICKEL (continued). Preparation of Nickeling Solutions. Adams' Process. Unwin's Process Weston's Process. Powell's Process. Potts' Process. Double Cyanide of Nickel and Potassium Solution. Solution for Nickeling Tin, Britannia Metal, &c. Simple Method of preparing Nickel Salts. Desmur's Solution for Nickeling Small Articles. Preparation of Nickeling Solutions. Although many solutions have been proposed, we may say, with confidence, that for all prac- tical purposes in the electro -deposition of nickel, a solution of the double sulphate of nickel and ammonium, wifh or without the addition of common salt, will be found the most easy to work and the most uni- form in its results, while it is exceedingly permanent in character if worked with proper care and kept free from the introduction of foreign matter. The preparation of a nickel bath from the pure double salt is exceedingly simple, as we have shown, and only needs ordinary care to keep such a solution in good working order for a very considerable period. In order that the reader may, however, become conversant with the various solutions and modifications which ingenious persons have from time to time introduced, we will, as briefly as possible, explain such of these processes as may appear to deserve attention, if not adoption. Boettger's original process having been already referred to, we will now describe Mr. Adams' modification of it, for which he obtained patents in this country, in France, and the United States, and which, after much costly litigation, and consequent loss to those who had become possessed of them, were proved to be unnecessary to the success- ful deposition of nickel by electrolysis. When the ordinary simple methods of preparing the double salts of nickel and ammonium are taken into consideration, it seems marvellous that Adams' exceedingly round- about process which no one with practical chemical knowledge would dream of following should have been considered worth contesting ; not to defend the process as such, which no one infringed, but to secure the sole right to deposit nickel by electro -chemical means, by any process whatever. And what was the real " bone of contention" ? It was based upon the most absurd " claim " ever allowed to become attached to a patent t which runs as follows : 2Q2 ELECTRO-DEPOSITION OF NICKEL. "The electro -deposition of nickel by means of a solution of the double sulphate of nickel and ammonia, or a solution of the double chloride of nickel and ammonium, prepared as [below] described, and used for the purposes [below] set forth, in such a manner as to be free from the presence of potash, soda, alumina, lime, or nitric acid, or from any acid or alkaline reaction." According to this, if any solution of nickel, no matter how pre- pared, which could be proved by analysis to be free from the sub- stances named (not one of which would be a necessary associate of nickel or of its double salts), such solution, if used in nickel-plating, would be an infringement of the patent! This we know was the impression of those who held the English patent, and we vainly endeavoured to show its fallacy. " Any solution of nickel which is free from these substances and used for plating purposes is an infringe- ment of our patent." That was the contention, and the owners of this patent believed themselves entitled to an absolute monopoly of the right to nickel-plate within the four quarters of the United Kingdom. Adams' Process. In preparing the solution, the inventor prefers to use pure nickel, but commercial nickel may be used. ''Commercial nickel," says the patentee, " almost always contains more or less of the reagents employed in the purification of this metal, such as sul- phate of lime, sulphide of calcium, sulphide of sodium or potassium, chloride of sodium, and alumina. When any of these substances are present, it is necessary to remove them. This can be done by melting the nickel, or by boiling it in water containing at least I per cent, of hydrochloric acid. The boiling must be repeated with fresh acid and water until the wash-waters give no indication of the presence of lime when treated with oxalate of ammonia. When the metal is purified by melting, the foreign substances collect on the top of the metal in the form of slag, which can be removed mechanically. If the nickel contains zinc, it should be melted in order to volatilise the zinc and drive it off. The crucible in such a case must not be closed so tightly C,3 to prevent the escape of the zinc fumes. If copper, arsenic, or antimony be present in the nickel, they can be removed, after the nickel is dissolved, by passing sulphuretted hydrogen through the solution. The acid to be used in dissolving the metal consists of I part strong nitric acid, 6 parts muriatic acid, and I part water. Nitric acid or muriatic acid may be used separately, but the above is preferred. A quantity of this acid is taken sufficient to dissolve any given amount of the metal, with as little excess of the former as pos- sible ; a gentle heat is all that is required. The resulting solution is filtered ; and to prepare the solution of the double sulphate of nickel and ammonium, a quantity of strong sulphuric acid, sufficient to con- vert all the metal into sulphate, is added, and the solution is then ADAMS PROCESS. 293 evaporated to dryness. The mass is then again dissolved in water, and a much smaller quantity than before of sulphuric acid is added, and the whole again evaporated to dryness, the temperature being raised finally to a point not to exceed 650 Fahr. This temperature is to be sustained until no more vapours of sulphuric acid can be detected. The resulting sulphate of nickel is pulverised, and thoroughly mixed with about one-fiftieth of its weight of carbonate of ammonia, and the mass again subjected to a gradually increasing tempera- ture, not to exceed 650 Fahr., until the carbonate of ammonia is entirely evaporated. If any iron is present, the most of it will be converted into an insoluble salt, which may be removed by filtration. The resulting dry and neutral sulphate of nickel is then dissolved in water by boiling, and if any insoluble residue remains, the solution is filtered. From the weight of nickel used before solution, the amount of sulphuric acid in the dry sulphate can be calculated. This amount of sulphuric acid is weighed out and diluted with four times its weight of water, and saturated with pure ammonia or carbonate of ammonia the former is preferred. This solution, if it is at all alkaline, should be evaporated until it becomes neutral to test-paper. The sulphate of ammonia of commerce may likewise be used, but pure sulphate of ammonia is to be preferred. The two solutions of the sulphate of nickel and sulphate of ammonia are then united, and diluted with sufficient water to leave i J to 2 ounces of nickel to each gallon of solu- tion, and the solution is ready for use. The object of twice evaporat- ing to dryness and raising the temperature to so high a degree is, in the first place, to drive off the excess of sulphuric acid ; and secondly, to convert the sulphate of iron, if it exists, into basic sulphate, which is quite insoluble in water. ' ' In order to give the best results, it is necessary that the solution should be as nearly neutral as possible, and it should in no case be acid. The inventor prefers to use the solution of a specific gravity of about 1*052 (water i-ooo), though a much weaker or still stronger solution may be used. At temperatures above the ordinary the solu- tion still gives good results, but is liable to be slowly decomposed. An excess of sulphate of ammonia may be used to dilute the solution, in cases where it is desirable to have it contain much less than I ounce of nickel to the gallon. " In preparing the solution of double chloride of nickel and ammo- nium, the nickel is to be purified and dissolved in the same manner as is described for the previous solution ; and it is to be freed from copper and other foreign matters in the same manner. The solution is then evuporated to dryness ; it should be rendered as anhydrous as possible. The salt is then placed in a retort, and heated to a bright red heat. The salt sublimes, and is collected in a suitable receiver, the earthy 20^ ELECTRO-DEPOSITION OF NICKEL. matter being left behind. The salt, thus purified, is dissolved in water, and to the solution is added an equivalent quantity of pure chloride of ammonium. The solution is then ready for use ; it may have a specific gravity of 1*050 to I'loo." The repeated evaporations recommended by Adams are wholly unnecessary in the preparation of the double sulphate of nickel and ammonium or the double chloride, for if the nickel be pure (and there is no difficulty in obtaining it in this condition), the ordinary method of dissolving the metal or its oxide, and subsequent addition of the ammonia salt and careful crystallising the double salt, would give the same result, with far greater economy, both of time and trouble. TTnwin's Process. This ingenious process, for which Mr. Unwin, of Sheffield, obtained a patent in 1877, is conducted as follows, and it will be seen that the salts of nickel and ammonia are thrown down in the form of a granular salt, readily soluble in water, by which the process of crystallisation is rendered unnecessary. He first prepares the sulphate of nickel ' ' by taking three parts of strong nitric acid (sp. gr. about 1*400), one P ar ^ ^ strong sulphuric acid (sp. gr. about 1*840), and four parts of water, all by measure, mixing them cautiously, and about half filling an open earthenware pan with the mixture. To every gallon of this mixed acid, I then add about two pounds of ordinary grain or cube nickel, and I heat the liquid by a sand-bath or other suitable means. If during the process of solution the action becomes inconveniently violent, I moderate it by the addi- tion of a little cold water. If the nickel entirely dissolves (except a email quantity of black matter), I add more of it, in small portions at a time, and continue the addition at intervals until it is in excess. When the production of red fumes has nearly, or entirely, ceased, or when the liquid becomes thick and pasty, from the separation of solid sulphate of nickel, I add a moderate quantity of hot water, and boil and filter the solution ; the deep green liquid so obtained is a strong solution of sulphate of nickel. If, from the circumstance of its pro- duction, I consider that it requires purification, I concentrate the solution by evaporation, until on cooling it yields a considerable percentage of crystals of sulphate of nickel ; these crystals I collect, wash with a little cold water, and redissolve in a moderate quantity of hot water, filtering again if necessary. When cold, the liquid is ready for further treatment. " I next prepare a strong solution of sulphate of ammonia, by dis- solving the salt in hot water, in the proportion of about four pounds of the salt to each gallon of water, and then filter the liquid if neces- sary, and allow it to become cold. I then obtain the pure double sulphate of nickel and ammonia by adding the above solution of sulphate of ammonia to that of the sulphate of nickel ; but I do no j UNWIN S PROCESS. 295 stop the addition of the solution of sulphate of ammonia, when suffi- cient has been added to combine with all the sulphate of nickel present, but I continue to add a large excess. I do this because I have discovered that the double sulphate of nickel and ammonia is far less soluble in the solution of sulphate of ammonia than in pure water, so that it is precipitated from its solution in water on adding sulphate of ammonia. I therefore continue adding the solution of sulphate of ammonia, continually stirring, until the liquid loses nearly all its colour, by which time the double sulphate of nickel and ammonia will have been precipitated as a light blue crystalline powder, which readily settles to the bottom of the vessel. I then pour off the liquid from the crystalline precipitate of double sulphate of nickel and ammonia, and wash the latter quickly with a strong, cold solution of sulphate of ammonia, as often as I consider necessary for its sufficient purification ; but I do not throw away this liquid after use, but employ it at my discretion for combining with fresh sulphate of nickel, instead of dissolving a further amount of sulphate of ammonia. If I desire to make a further purification of the double sulphate of nickel and ammonia, I make a strong solution of it in distilled water, and add to the liquid a strong solution of sulphate of ammonia, by which means the double sulphate is precipitated in a very pure condition, and is separated from the liquid by filtration, or by other convenient means, and then dried, or used direct as may be desired ; the liquid strained away can be employed, instead of fresh solution of sulphate of ammonia, for combining with more sulphate of nickel, or for washing the precipitate of the double sulphate." Western's Process. Mr. Edward "Weston, of Newark, N.J., having observed that boric acid, when added to nickel solutions, pro- duced favourable results in the electro -deposition of nickel, obtained a patent for " the electro -deposition of nickel by means of a solution of the salts of nickel containing boric acid, either in its free or com- bined state. The nickel salts may be either single or double." The advantages claimed for the boric acid are that it prevents the deposit of sub-salts upon the articles in the bath, which may occur when the bath is not in good condition. Mr. "Weston further claims that the addition of this acid, either in its free or combined state, to a solution of nickel salts renders it less liable to evolve hydrogen when the solu- tion is used for electro -deposition ; that it increases the rapidity of deposition by admitting the employment of a more intense current, while it also improves the character of the deposit, which is less brittle and more adherent. Mr. Wahl, after extended practical trials of Mr. Weston' s formula, states that they have " convinced him of the substantial correctness of the claims of the inventor," and he adds, " "Where the double sulphate of nickel and ammonia is used, the addi- 296 ELECTRO-DEPOSITION OF NICKEL. tion of boric acid, in the proportion of from I ounce to 3 ounces to the gallon of solution, gives a bath less difficult to maintain in good working order, and affords a strongly adhesive deposit of nickel. The deposited metal is dense and white, approaching in brilliancy that obtained from the solution of the double cyanide." The formula for preparing the solution is Double sulphate of nickel and ammonia . . .10 parts. Boric acid, refined . . . . . 2j to 5 Water 150 to 200 Powell's Process. This inventor claims to have discovered that benzoic acid, added to any of the nickel salts, arrests, in a marked degree, the tendency to an imperfect deposit, prevents the decompo- sition of the solution, and consequent formation of sub-salts. The proportion of benzoic acid to be added to the bath is said to be one- eighth of an ounce to the gallon of solution. This bath has been favourably spoken of. Powell also gives the following formulae for nickel baths : 1. Sulphate of nickel and ammonia . . . .10 parts. Sulphate of junmonium 4 Citric acid ........ i Water 200 The solution is prepared with the aid of heat, and when cool, a small quantity of carbonate of ammonia is added until the solution is neutral to test paper. 2. Sulphate of nickel . , ' . . . . 6 parts. Citrate of nickel . ... ... 3 Phosphate of nickel . . . . . 3 Benzoic acid . . , . ' . ' , . i ,, Water . . 200 3. Phosphate of nickel . . .'''.*. . 10 parts. Citrate of nickel 6 Pyrophosphate of sodium . . . .- icj Bisulphite of sodium . . . . . . i Citric acid . . . .... . 3 Liquid ammonia . . .... . 15 Water . . . . <.'... . 400 These solutions are said to give good results, but the very compli- cated nature of the latter almost takes one's breath away. Potts' Process. In 1 880, Mr. J. H. Potts, of Philadelphia, patented an improved solution for the electro -deposition of nickel, which consists in employing acetate of nickel and acetate of lime, POTTS' PROCESS. 297 with ' ' the addition of sufficient free acetic acid to render the solution distinctly acid." The formula is given below : Acetate of nickel 2! parts. Acetate of calcium 2j Water . . . . -. - . .100 To each gallon of the above solution is added I fluid ounce of acetic acid of the sp. gr. 1*047. Mr. Potts first precipitates the carbonate of nickel from a boiling aqueous solution of the sulphate, by the addition of bicarbonate of soda, then niters and dissolves the well- washed precipitate in acetic acid, with the aid of heat. " To prepare this bath, dissolve about the same quantity of the dry carbonate of nickel as that called for in the formula (or three-quarters of that quantity of the hydrated oxide) in acetic acid, adding the acid cautiously, and heating until effervescence has ceased and solution is complete. The acetate of calcium may be made by dissolving the same weight of carbonate of calcium (marble dust) as that called for in the formula (or one-half of the quantity of caustic lime), and treat- ing it in the same manner. Add the two solutions together, dilute the volume to the required amount by the addition of water, and then to each gallon of the solution add a fluid ounce of free acetic acid as prescribed." In reference to the above solution, Wahl says that he has worked it under a variety of circumstances, and has found it, in many respects, an excellent one. " It gives satisfactory results," he states, ' ' without that care and nicety in respect to the condition of the solution and the regulation of the current which are necessary with the double sulphate solution. The metallic strength of the solution is fully maintained, without requiring the addition of fresh salt, the only point to be observed being the necessity of adding from time to time (say once a week) a sufficient quantity of acetic acid to maintain a distinctly acid reaction. It is rather more sensitive to the presence of a large quantity of free acid than to the opposite condition ; as in the former condition it is apt to produce a black deposit, while it may be run down nearly to neutrality without notably affecting the character of the work. The deposited metal is characteristically bright on bright surfaces, and requiring but little buffing to finish. It does not appear, however, to be so well adapted for obtaining deposits of extra thickness as the commonly used double sulphate of nickel and ammonium. On the other hand, its stability in use, the variety of conditions under which it will work satisfactorily, and the trifling care and attention it calls for, make it a useful solution for nickeling." Double Cyanide of Nickel and Potassium Solution. This was 298 ELECTRO-DEPOSITION OF NICKEL. one of the earliest solutions used for depositing nickel, and is capable of yielding an exceedingly white deposit. Though neither so econo- mical nor so susceptible of yielding stout deposits of nickel as the ordinary double sulphate or double chloride, it may be advantageously employed when only a thin coating of a fine white colour is desired. It is stated to be somewhat extensively used in some large nickel- plating works in the United States. To prepare the solution, pure nickel or oxide of nickel is dissolved in either of the mineral acids ; a mixture of hydrochloric and nitric acids, in the proportion of four parts of the former to one of the latter, may be used, an excess of the metal being taken to fully neutralise the acid. The solution is then evaporated and set aside to crystallise. The crystals, after being well drained and quickly rinsed in cold water, are next dissolved in water by the aid of heat, and when the solution has become cold a solution of cyanide of potassium is carefully added, with stirring, until all the metal has been thrown down in the form of cyanide of nickel. Care must be taken not to add an excess of cyanide. The supernatant liquor is now to be poured off, and the precipitate washed repeatedly with water. A strong solution of cyanide is next added, with stirring, until all the cyanide of nickel is dissolved. A small excess of cyanide is then to be added, when a reddish-brown solution of double cyanide of nickel and potassium will result, which, after filtering, is ready for use. The solution should be as concentrated as possible, almost to the point of saturation. Solution for Nickeling Tin, Britannia Metal, &c. The follow- ing formula has been recommended for coating tin, Britannia metal, lead, and zinc, as also brass and copper : Sulphate of nickel and ammonium . . .10 parts. Sulphate of ammonium . . . . . . 2 Water 300 The salts are to be dissolved in boiling water, and when cold the solution is ready for use. For nickeling cast and wrought iron and steel the following bath is recommended : Sulphate of nickel and ammonium . . .10 parts. Salphate of ammonium . . .- . . ij Water . . . . . . . ' . . 250 Simple Method of Preparing Nickel Salts. To make the double chloride of nickel and ammonia take, say, 2 ounces of pure cube nickel, or oxide of nickel, and dissolve in hydrochloric acid, to which a little nitric acid may be added, taking care not to have an excess ; apply gontle heat to assist the chemical action. When the evolution of gas has ceased dilute the resulting solution with cold water to make about I quart of liquor ; now add liquid ammonia gradually, stirring after DESMUR S SOLUTION. 2pQ each addition, until the solution is neutral to test-paper ; now dissolve I ounce of chloride of ammonium (sal-ammoniac) in sufficient water, and add this to the former solution ; evaporate the mixture until crystals begin to form, then allow it to cool and crystallise gradually ; next pour off the clear liquor, and repeat the evaporation to obtain a second batch of crystals ; in the latter operation the solution may be evaporated to dryness. Finally, mix all the resulting products together and dissolve in about three pints of hot water, filter, and make up to about one gallon by the addition of cold water. The solution should have a specific gravity of 1*050 to i'O75. The Double Sulphate of Nickel and Ammonium may readily be formed by dissolving oxide or carbonate of nickel in dilute sulphuric acid (i part acid to 2 parts water). The resulting solution is then to be neutralised with ammonia and crystallised. To each pound of the dry crystals add I pound of pure sulphate of ammonia, dissolve the mixed salts, evaporate the solution, and re -crystallise. Cube or grain nickel may also be dissolved in a mixture composed of I part sulphuric acid and 2 parts water, with the addition of a small quantity of nitric acid, moderate heat being applied as before. The solution is then to be evaporated and set aside to crystallise, and to convert the sulphate of nickel into the double salt, sulphate of ammonia is to be added in the same proportion as before ; the mixed salts must be dissolved, filtered, and crystallised. In making up a bath from the double sulphate prepared by either of the above methods, about 12 ounces of the dry crystals are to be taken for each gallon of bath, and the crystals should be dissolved in sufficient hot water, the solution filtered, and the requisite quantity of cold water added to make up the full quantity of the solution in the proportions given. At the temperature of 60 Fahr. the bath should have a specific gravity of about 1-52. It is necessary to state that the nickel employed should be pure, which can only be relied upon by obtaining it from some well-known respectable house. Desmur's Solution for Nickeling Small Articles. The author is indebted to M. Desmur for the following formula for coating small articles, which we recommend to the attention of those whose trade chiefly lies in nickeling struck work, such as umbrella -mounts, and the like : Double sulphate of nickel and ammonium . 7 kilogrammes Bicarbonate of soda ..... 800 grammes. Water . . . 100 litres. The bicarbonate of soda must be added when the nickel solution is warm, in small quantities at a time, otherwise the effervescence which occurs may cause the solution to overflow. The bath is to be worked up to nearly boiling point. If, after working for some time, the < deposit becomes of a darkish colour, add a small lump (about the size 30O ELECTRO-DEPOSITION OF NICKEL. of a nut) of sulphide of sodium, which will remedy it. ' ' Of all the solutions of nickel which I have tried," says M. Desmur, " this has, without doubt, given me the best results, both as to quickness of working and whiteness of deposit, which is equal to that of silver. Nickel deposited from this solution can be burnished. If the nature of the articles to be nickeled will not allow them to be either polished or burnished, they may be rendered bright by first dipping them in nitric acid and afterwards passing them rapidly through a mixture of old nitric acid dip (already saturated with copper), sulphuric acid, greasy calcined soot, and common salt." .U.COBV. CHAPTER XXIII. ELECTED -DEPOSITION OF NICKEL (continued). Preparation of the Work for Nickel-plating. The Scouring Tray. Brass and Copper Work. Nickeling small Steel Articles. Nickeling small Brass and Copper Articles. Nickeling by Dynamo-electricity. Nickeling Mullers, Sausage Warmers, &c. Nickeling Bar Fittings, Sanitary Work, &c. Nickeling Long Pieces of Work. Dead Work. Nickeling Stove Fronts, &c. Nickeling Bicycles, &c. Nickeling Second-hand Bicycles, &c Nickeling Sword-scabbards, &c. Nickeling Harness Furniture, Bits, Spurs, &c Nickeling Cast-iron Work. Nickeling Chain Work. Re-Nickeling Old Work. Nickeling Notes. Preparation of the Work for Nickel-plating. Since the various metals ordinarily coated with nickel require different treatment, it will be more convenient to treat them under their re- spective heads, by which the intending nickel-plater will become more readily conversant with the mani- pulation requisite in each particular case. All the Fig. 105. preliminary arrangements of nickel bath, batteries, dips, &c., being complete, the work, as it is received from the polishing shop, should be placed in regular order upon a bench, the name of each customer being indicated by a ticket for each group of work, so as to prevent confusion. Small work is generally handed into the plating-room upon shallow trays, of the form indicated in Fig. 105. These trays are usually about 2 feet long by 15 inches wide, and about 3 inches deep ; they are made of ordinary inch deal, planed on both sides, and the corners are bound with stout sheet iron. The trays are made of various sizes to suit the different classes of work to be conveyed in them. The reader is referred to another chapter for a description of the process of polishing. The Scouring Tray. This apparatus, which has to be subjected to much wear and tear, requires to be well put together, and must be 302 ELECTRO-DEPOSITION OF NICKEL thoroughly water-tight. A sketch of the scouring tray generally adopted is shown in Fig. 106. It is usually made from two-inch deal, planed on both sides ; the joints are rendered water-tight by means of india-rubber, and the various parts are well bound together by screwed bolts and nuts. The dimensions may be 6 or 8 feet long (inside), 2 feet 6 inches wide, and about 15 or 18 inches deep. It is divided into two equal compartments by a wooden partition, and a stout shelf is fixed across one compartment, upon which is a small block of wood about 7 or 8 inches long, and 2 inches square, secured to the shelf, by screws, from beneath, for scouring small articles. A water-tap, [\ ^ 1 E= B Fig. 106. with india-rubber hose, is placed at a convenient distance above the tray, by which means either compartment may be filled at pleasure. At the corner of either compartment of the scouring tray is a flanged exit pipe, let into the bottom at the far corner, to allow the tray to be emptied when required. The second compartment is used as a rinsing trough. The exit pipes are furnished with a wooden plug, which the workman withdraws when he desires to run off the water from either compartment. A wooden shelf is generally fixed at a convenient dis- tance above the back of the scouring tray, to hold various brushes, pumice-box, or other tools required in preparing work for the bath. Brass and Copper Work. The articles are first suspended, by BRASS AND COPPER WORK. 303 means of short lengths of copper wire, in the hot potash bath, where they are allowed to remain until ready for scouring. The ' ' slinging wires" for this purpose, as also for suspending the articles in the nickel bath, should be of various thicknesses, according to the weight they have to sustain, and it is a good plan to keep bundles of these wires, cut up into regular lengths, bound together by a piece of the same wire, so that they may be readily withdrawn as required. The articles being taken out of the potash bath, one by one, or a few at a time, according to their size, are at once plunged into the water in either compartment of the scouring tray. They are next subjected to the operation of scouring. Scouring. This usually consists in well brushing the work with finely powdered pumice and water, by means of hog-hair brushes. Some platers prefer a mixture of pumice and rottenstone for brass work, as being rather less cutting, and therefore less liable to scratch the work so severely as the pumice and water alone. The author's son, Mr. A. N. Watt, has succeeded well in employing ordinary whiting in scouring brass and copper work, which, while suffi- ciently cleaning the articles, enables them to come out of the nickel bath in a much brighter condition than when pumice is used, and as a natural consequence the work requires less time and trouble in finish- ing. "We believe that recently slaked lime, either alone or mixed with whiting, would be better still, were it not for the fact that the caustic lime would be injurious to the hands of the workmen. In scouring the work it is placed on the shelf across the scouring tray ; the brush is then dipped in water and afterwards in the powdered pumice, or other material which is kept in a wooden box upon the back shelf and the article is well brushed all over, beginning at one end, and then turning the article round to brush the other ; a final brushing is then given all over, as quickly as possible, so as to render the surface uniform. As each article is brushed it is rinsed in clean water, the slinging wire is then attached, and the article next dipped, for an instant, in the cyanide dip, again well rinsed, and immediately after suspended in the nickel bath, where it is allowed to remain from four to eight hours, according to whether the work is to be moderately or thoroughly coated with nickel. As we have before observed, all work which is to be bright when finished must be polished before being nickel-plated. If, however, it were to be immersed in the nickel bath without any further preparation (unless a very slight coating of nickel were given), even if perfectly free from greasy matter and oxide upon its surface, the nickel would surely strip or peel off. Hence the operation of scouring is adopted not alone to render the surface of the metal absolutely clean, but to give it an almost imaginary decree of roughness. It is a fact well known to 304 ELECTEO-DEPOSITION OF NICKEL. electro -depositors that when a surface of metal is perfectly bright any other metal deposited upon it will readily separate. The surface may be all but bright, and the two metals will adhere more or less firmly ; but if it is absolutely bright, the metals have little or no cohesion. In scouring-, therefore, great care must be taken that the application of the brush and pumice has been perfectly uniform all over the work, and that the bright lustre given to it by the polisher has been thoroughly removed. To produce this result, the work does not entail laborious scrubbing, but is accomplished by a brisk brushing, taking care to keep the brush well charged with the pumice. "We have seen men, improperly instructed in this respect, who have first dipped the brush in water, then in the pumice powder, and finally in the water again, before applying it to the work, whereby they actually washed away the material before the brush was applied ! Again, it is a common error to dip the brush in the pumice before shaking the superfluous water from it, which not only causes the powder to become deluged with water, and a considerable portion of it to be wasted, but in this extremely wet condition it has little effect upon the surface to be cleaned. The brush should only be moist when dipped in the powder, in which state it will take up sufficient material to spread over a considerable surface, and will then do its required work effectually, with very little waste. Some scourers are very wasteful in this respect, and as a rule their work is never properly cleaned, or pumiced. The brushes employed in scouring are made from hog bristles, and are supplied, for the general purposes of the plater, of various widths, and are known as one -rowed, two -rowed, three-rowed, and four-rowed brushes, each terminating in a suitable handle (see Fig. 94). The brushes, in their separate sizes, may belaid upon the shelf behind the scouring tray, so as to be ready to hand when required for use, and they should on no account be used for any other purpose than scouring the work. New brushes may be dipped for an instant in the potash bath, and immediately rinsed, by which any greasy matter communicated to the hairs or bristles during the manufacture will be rendered soluble, and will afterwards wear away in use. This precaution is not altogether unnecessary, since these brushes have frequently been used by workmen for brushing their clothes, and sometimes even their hair. Immersing the Work in the Bath. When we bear in mind that the nickel anodes have a stationary or fixed position in the bath, and that consequently a very large surface of the positive electrode is exposed, it will be at once apparent that some means must be adopted, when the first batch of articles are being placed in the bath, to prevent the deposit from taking place too rapidly (owing to the excess of anode surface), and thereby causing the work to "burn," as it is called. NICKELING SMALL STEEL ARTICLES. 305 When dynamo or magneto -electric machines are employed, resistance coils are used to regulate or control the force of the current, as we shall explain hereafter ; but although such coils are less necessary when depositing by battery power, some other equally effective means must be adopted. The most simple plan is to hook one of the anodes on the negative conducting rod, at its farthest end from the battery, and there to leave it until the rod is nearly supplied with work, when it may be removed and put in its proper place on the positive rod. By adopting this practice with each suspending rod in turn the " burn- ing " of the work is entirely prevented, and deposition takes place, as it should do, gradually, which is of special importance in the earlier stages of the operation. When work of moderate dimensions as brass taps, for example and very small articles are in hand for nickeling, the larger work should be put into the bath first, and the smaller work then introduced between other pieces of larger work. It is also usual to commence suspending the work from the end of the rod nearest the battery (Avhere the power is weakest) rather than from the opposite end. Small articles such as screws, for example should not be slung singly, but several of them CLLI I ffl '~b suspended from the same wire, as in Fig. 107, in siich a way as not to be in contact with each other. Nickeling Small Steel Articles. This class of work, after cleaning, immersion in the acid dip, and Fig. 107. rinsing, should be suspended in the bath, if prac- ticable, between other articles of larger dimensions, so that depo- sition may take place slowly and gradually ; otherwise the articles are very liable to strip. This precaution is specially necessary in nickeling small dentists' tools, as excavators, &c., which, when ex- posed to too strong a current, are apt to burn at the lower end and strip. In nickeling such work the rule is, after the article has be- come " struck" (that is, coated all over), to allow the deposit to take place very slowly, especially during the first half -hour's immersion. When battery power is used, from one to two hours' immersion will be sufficient for a serviceable coating upon the smaller dental tools, but a somewhat longer period say, up to three hours should be given to dental forceps. When a dynamo -machine is employed, about half this time will be sufficient. It is very important that steel work should be placed in the bath immediately after being cleaned, since even a few moments' exposure to the air or immersion in water will cause an invisible film of oxide to form on the surface, which will prevent the nickel from firmly adhering to the steel. After nickeling, the articles ore rinsed in hot water and handed to the finisher, who gives them the X 306 ELECTRO-DEPOSITION OF NICKEL. necessary Irigh polish. Small steel or iron articles which are not required to receive a stout coating of nickel are first steeped for a short time in the potash bath, and after being rinsed are dipped for a moment in the hydrochloric acid dip, again rinsed, and put into the nickeling bath, without any preparatory scouring, and given a short immersion only say, half -an -hour. Such work is generally finished by being dollied only, which brings up the surface to its proper brightness. Nickeling Small Brass and Copper Articles. When these have to receive a good coating and afterwards to be finished bright, they must be scoured after polishing, and treated in all respects the same as larger work. Articles which are not required to be stoutly nickeled, however, but only moderately well coated with this metal, may be polished with the rouge composition referred to in another chapter, instead of with lime in the usual way, and then placed in the bath without previous scouring. When they have received a moderate coat- ing of nickel they are rinsed in hot water, and afterwards finished with the mop, or dolly, with the aid of the same composition. This method of treating small brass work which we believe is of American origin is especially suitable for umbrella mounts, reticule and purse frames, cheap fancy work, and such articles as are not liable to much friction in use. Small brass articles which are not required to be bright are first put into the potash bath for a short time, and after rinsing they are dipped in ordinary dipping acid, again well rinsed in several waters, and then put into the nickel bath, in which they receive a deposit according to the nature and quality of the work and the price to be paid for it, a short immersion, in many cases, being all that is given when the price is low. Nickeling by Dynamo -electricity. Although a very consider- able amount of work of all kinds is coated with nickel by battery current, by far the greater portion passes through the hands of those who adopt dynamo or magneto -electric machines as the source of electricity. Indeed, if it were not for the great advantages which these machines present in the deposition of this metal, the art of nickel- plating would never have attained its present magnitude. In arrang- ing a nickeling plant upon a large scale, the baths should be placed parallel to each other, having sufficient space between each vat for the free passage of the workmen ; and the dynamo -machine should be stationed conveniently near the vats, so as to be under the immediate control of the plater. The conducting wires should be so arranged that the current may be applied to one or more of the baths, as occasion may require, and this may be most conveniently effected by fixing two stout brass or copper rods, by means of insulating brackt ts, to the wall of the apartment nearest the nickel tanks ; these leading 3 o8 ELECTRO- DEPOSITION OF NICKEL. wires or conducting rods must have attached to them a series of binding screws, corresponding in number to the connecting screws of the suspending rods. A large form of nickel tank, capable of holding from 250 to 500 gallons of solution, is shown in Fig. 109. To connect the machine with the leading rods stout copper wire is used, the thickness of which is regulated according to the power of the machine. For a medium -sized Weston, half -inch copper wire is generally used, but for larger machines the wire employed is usually three -fourths to one inch in thickness. To convey the current from the leading rods to the baths, the wire need not be so stout as in the former case, about one- half the thickness being sufficient. To give motion to the machine a counter- shaft is usually fixed overhead, with its driving pulley immediately in a line with the pulley of the machine, the two being connected by a belt in the usual way. The counter -shaft, an im- Fig. 109, proved form of which has been introduced by Carlyle, is shown in Fig. no, is furnished with a long iron handle within reach, by the raising or lowering of which the belt is placed on the fast or loose pulley of the shaft, according to whether the machine is required to run or stop. To regulate the amount of current entering the respective baths, a resistance coil is either attached to the end of each bath or fastened to the wall facing the end of each vat, and these coils are interposed in the circuit by means of short conducting wires. (See Fig. 108.) In working large tanks of nickel solution for coating articles of moderate size, as taps, spurs, bits, table lamps, &c., three rows of anodes are generally used, which are thus disposed : one row of anodes is suspended from a conducting rod on each side of the tank, and the third row is placed in the centre of the bath, midway between the other two. Two rods for supporting the work to be nickeled are placed between the side and centre rows of anodes, by which arrange- ment the suspended articles will be exposed to the action of two anode eurfaces. The three anode rods must be united at their ends by means KICKELING BY DYNAMO-ELECTRICITY. 309 of thick copper wire, in which case one binding screw only, attached to the end of one of the side rods, will be necessary to connect the anodes with the positive leading wire of the machine ; or a separate binding screw may be connected to the end of each rod, and the con- nection with the leading rods completed with short lengths of stout wire. The latter plan is the best, since one or more rows of anodes Fig. no. can be more readily thrown out of circuit by simply disconnecting the wire from the binding screw at the end of the rod. Nickeling Mullers, Sausage Warmers, &c. Large brass and copper articles such as beer and wine mullers, for example owing to the extent of surface they present, and their peculiar form, require a different arrangement of the anodes to that which is adopted for ordinary work, and for this reason : it is well known that all metals re- ceive the deposit most freely upon the surfaces facing the anode ; and although in gilding, silvering, and coppering the deposit takes place to a moderate extent upon those sur- faces of an article which do not directly face the anode, in the case of nickel it is quite different, for under the same conditions little or no deposit would take place at the oppo- ff site parts of the article unless an anode were suspended ^e on each side of it, as in the arrangement we have de- scribed. Since mullers, and articles of the class to which they belong, present an extensive convex surface, it is necessary, in order to secure a uniform coating of nickel, to surround such work with anodes as far as is practicable. This is ordinarily done in the following manner : The centre row of anodes is first removed ; two short brass rods are then placed across the other positive rods, about 2 feet apart, and upon each of these is suspended one or more anodes, according to their width. The centre conducting rod, lately occupied by the anodes, is now used as the suspending rod for the muller. Where more than one nickel bath is employed, it is best to keep one of these specially for mullers and other large work, in which case two rows of anodes only and one centre negative rod, should be applied. The bath used for nickeling mullers should be kept covered with a frame, upon which oiled calico is stretched, to protect the work from dust. The drawing (Fig. 1 1 1) 310 ELECTRO-DEPOSITION OP NICKEL. shows the relative position of the muller and the surrounding anodes. When the article has been in the bath some time, its position must be reversed that is to say it must be inverted so as to equalise the coat- ing as far as possible, since the deposit always occurs most energetic- ally at the lower surface of the article in the solution. In a loo-gallon bath only a single muller, or similar article, could be nickeled at one time ; in other words, it should have the whole bath to itself. When dynamo -machines are employed, however, the baths seldom consist of less than 250 gallons of solution. In nickeling the above class of work great care and smartness of manipulation are necessary. The work requires to be well and briskly brushed with pumice after removal from the potash bath, and after being rinsed is passed through the cyanide dip for a moment, and again well rinsed, and no time should now be lost in getting it into the nickel bath, and connecting it to the conducting rod. Soon after immersion the characteristic whiteness of the nickel should be visible upon its surface, as evidence that cur- rent is sufficiently strong to do the work required of it. Such being the case, the I article must be left for awhile, after which it may be gently moved up and down by its slinging wires (but not out of the solution) to disperse any dusty particles that may have settled upon Fig. in. its u PP er surface, since these, how- ever slight and imperceptible, will sometimes cause a rough and irregular deposit, which will give some trouble to the polisher when finishing the article. When plating work of this description in a bath which has been long in use, the anodes should be arranged as described some time before a muller is placed in the bath, so that the sediment (which always accumulates at the bottom of the vessel), if disturbed, may have time to subside ; and in placing the article in the bath care should be taken to lower it gently, so as not to disturb the " mud," if we may call it so, at the bottom. The opposite of this careful treatment needs only to be tried once to make the plater exceedingly particular thereafter. However careful the operator may be, it sometimes happens that certain parts of the article will become bare, or " cut through," as it is termed, during the process of finishing, in which case it is sent back from the polishing-room to the plater, who must in some way deposit nickel upon the exposed surface. This is accomplished by applying the " doctor," by which means a coating of metal is deposited upon the naked spot in the following way : a piece of stout copper wire, about a foot in length, is bent in the form of a hook at each end ; a NICKELING BAB FITTINGS, ETC. 311 small piece of nickel, about an inch and a half square, is attached to one of the hooks, and this is wrapped up in several folds of rag, secured to the wire by twine. The other hook is connected by a long copper wire to the anode rod, and the article to be doctored connected in tho same way to the negative rod. Now dip the rag-end of the wire in the nickel bath, and apply it to the bare spot (which should be previously brushed over lightly with pumice), keeping it in contact for a few seconds, then dip it in the bath again and apply as before, repeating the operation every half -minute or so, until a sufficient deposit of nickel has been given to the spot to enable the finisher to apply the "dolly," and thus render this part as bright as the rest of the article. Although this may not be considered a very conscientious method of getting over the difficulty, unless performed with patience, so as to impart something more than a mere film upon the bare place, it must be borne in mind that if the entire article were to be re -nickeled this would involve an amount of trouble and expense of labour which would never be compensated for. The "doctoring," however, should always be done well, and since the articles to which it is usually applied are rarely subjected to such friction as would affect so hard a metal as nickel, the defective portion of the work may cause little or no annoy- ance to the owner. Nickeling Bar Fittings, Sanitary Work, &c. Articles of this description require to be thoroughly well coated with nickel, and finished in the best possible manner. Before submitting such work to any preparatory process, the plater should carefully examine each piece to ascertain if it has been properly polished and all scratches and file marks obliterated, since if any of these be present after the article is nickeled and finished they will greatly impair the appearance of the work, while the finisher will be quite powerless to remove them without cutting through the nickel deposit. A careful examination of all work should be made by the plater before allowing it to enter the potash bath, and since in most establishments the polishing and finishing are done on the establishment, a proper understanding should exist between the finisher and plater as to the absolute necessity of having the work finished in the best possible manner. The articles, after being approved by the plater, are handed to the scourer, who con- nects a stout copper wire to each piece, and slings them to the suspend- ing rod of the potash bath ; after a short time these are removed, one or more at a time, according to their size, and after rinsing are taken to the scouring tray, where they are well brushed with pumice, then well rinsed in the water-trough of the scouring tray, and dipped for a moment in the cyanide dip. After being again well rinsed they are promptly suspended in the nickel bath. The articles should be thoroughly rinsed after being in the cyanide dip to prevent the intro- 312 ELECTRO DEPOSITION Otf NICKEL. duction of this substance into the nickel bath. About two and a half hours' immersion in the bath, when a dynamo-machine is used, will be sufficient time to obtain a good deposit. It may be well to remark here, that however desirous a nickel -plater may be to give a good thick coating to his work, there is a limit, as far as nickel is concerned, which must on no account be exceeded ; otherwise the deposited will strip or peel off the work, even without touching. Indeed, we have known the nickel, when the articles have been too long in the bath, to separate from the work and curl up in flakes, while a second deposit has taken place upon the parts thus deprived of metal. nickeling Long Pieces of Work. Hand-rails, cornice poles, the framework of shop fronts, and other long pieces of work, require to be nickeled in a bath of suitable dimensions : for this purpose a tank of the form shown in Fig. 112 is generally used, which is supplied with a series of short anodes to suit the form of the vessel. Such a tank should be about 12 feet long, 20 inches deep, and about 1 8 inches wide. Since articles of this character do not very fre- Fig. 112. quently come into the hand of the plater, it is unnecessary to employ special dipping baths for potash and cyanide ; the hot potash liquor may be poured over the article from a jug, beginning at one end, and continuing the operation until the whole surface has been washed over with the hot liquor. After rinsing and scouring, the cyanide dip may be applied, quickly, in the same way. The article must now be well rinsed and got into the bath as promptly as possible. Dead Work. Ships' deck lamps, and many other classes of work, which are not required to be polished, but left dead that is, just as they come out of the nickel bath are potashed, as usual, and after scour- ing and rinsing placed in the bath and allowed to remain until suffi- ciently coated. Since work of this kind should look as white as deposited nickel is capable of becoming, it is necessary, more especially during the last few minutes' immersion, to employ a strong current. When the articles are sufficiently coated they must be taken out of 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. Since dead nickel is very readily stained or soiled even when touched with clean hands, the work should be handled as NICKELING BICYCLES, ETC. 313 little as possible before being sent home to the customer. We have known instances in which dead nickel work, which from its silvery whiteness was pleasing to behold after removal from the bath, looked dirty and patchy before delivery to the customer, merely through the careless fingering to which it had been subjected by the warehouse- man and others. Nickeling Stove Fronts, &c. These are usually nickeled in a vat specially constructed for the purpose, the form of which is shown in Fig. 113. It consists of a wooden vessel about 5 feet deep, 4 feet long, and about 18 inches wide, held together by bolts and screws, and is sometimes lined with pitch owing to the difficulty of lining such a vessel with lead. The anodes should be at least 30 inches long, and since only the fronts of stoves require to receive the coating of nickel, a single row of anodes only is necessary. This class of work is usually sent to the plating works in a polished state that is, such parts as are to be bright are put in this condition by the manufacturers. To prepare the front for plating, it is first put into the potash bath as usual, and after a short immersion is well rinsed and scoured with pumice ; it is next dipped in the hydrochloric acid dipping bath, again rinsed, and then put into the nickel vat with all possible despatch. After about two to three hours' immersion, the article is steeped in hot water, and when dry is handed to the finisher. Large pieces of orna- mental iron work which have to be left dead may be also nickeled in the " stove bath." Nickeling Bicycles, &c. When this class of work is sent to the plater in parts, these may be nickeled in the ordinary bath with the exception of the rim of the wheel, and all parts must be polished and treated in the same way as other steel work. A convenient method of suspending bicycle spokes in the bath is shown in Fig. 114. The copper slinging wire is simply coiled into a series of equidistant loops, through which the wires of the spokes pass freely, and when a sufficient number have been wired in this way the two ends of the slinging wire are pulled with both hands, by which the loops become tightened and the spokes held firmly. They are then lowered into the bath and suspended from the negative rod as shown in the engraving. After a short immersion, each spoke is shifted a little, so as to allow the wire mark to be coated, and this operation is repeated several Fig. 113. 3^4 ELECTRO-DEPOSITION OF NICKEL. times during their immersion in the bath, so that the coating may be as regular as possible. "With a dynamo-machine a sufficient coating will be obtained in about an hour and a half. In nickeling the back- bone and fork of a bicycle, and the larger parts of tricycles, these pieces should be frequently shifted in the bath to ensure uniformity of deposit, for it must be borne in mind that from the peculiar curved form of the backbone, for example, the parts farthest from the anodes will receive the least de- posit. In cases where the bath is not large enough to take in the entire rim of a large bicycle wheel, it is usual to nickel one -half at a time ; when this has to be resorted to, great care must be taken to well clean the line where the deposited metal and the bare steel meet, otherwise, when depositing upon the second or third portion of the rim, F jg j I4> the nickel will strip at the junction of the separate deposits. In each case, a portion of the nickeled part should be immersed in the bath with the uncoated surface. "When finishing the rim the polisher should be par- ticularly careful with these junctions of the separate deposits, otherwise he may readily cut through the nickel and expose the underlying metal. In establishments where the nickeling of bicycles forms a special branch of the business, baths of suitable dimensions are em- ployed for depositing nickel upon the larger pieces of bicycle and tricycle work. Nickeling Second-hand Bicycles. Some few years ago, when nickel-plated bicycles first appeared in the market, the whole bicycle fraternity, who had been accustomed to plain steel or painted wheelers, looked with admiration, if not with envy, upon those who appeared amongst them upon their brilliant and elegant nickel-plated roadsters. At the time we speak of there was a rush of bicyclists at the various nickel-plating works, and anxious inquiries were made as to the possi- bility of nickeling bicycles which had become hideously rusty from neglect, or even those which had been more carefully treated. Could not a bicycle be popped in the solution, or whatever it was, and covered with the stuff, so as to come out bright like those in the shop win- dows ? Questions such as these were asked, even with apparent seriousness. One firm, after consulting the foreman, determined to undertake the task of nickeling one of these second-hand bicycles, and after a good deal of trouble since it was probably the first time such a thing had been attempted the task was accomplished with consider- able success, and the owner cheerfully paid the cost of its transmuta- tion, three pounds ten shillings a price that in these days of brisk NICKELING SWORD SCABBARDS. 315 competition would scarcely be thought of. Since the period referred to, the nickeling of bicycles has become an ordinary matter of detail in most nickel-plating works. In preparing a bicycle for nickeling, the principal parts must first be taken asunder. The head nut is first unscrewed to liberate the backbone ; the bolt which runs through the fork of the backbone must next be removed, by which the small wheel becomes dislodged ; the bolt is next withdrawn from the hub of the large wheel, which liberates the fork ; the spring is next disconnected by removing the screws at the head and back of the spring. All these parts, with the exception of the wheels, must pass through the hands of the polisher. It is not usual to remove the spokes, which in the case of a much-used machine would entail considerable risk, since much difficulty would occur not only in removing but in replacing them. The wheels are, therefore, nickeled entire, but before doing so they must be polished in the best way possible by hand, since it would not only be dangerous, but impracticable, to polish them at the lathe. The spokes and other parts of the wheel are first well rubbed with emery-cloth of various degrees of fineness, and then hand-buffed with chamois-leather, first with trent-sand, and afterwards with lime, as good a surface as possible being produced by these means. The wheels and other parts, when polished, are placed in the hot potash bath, where they are allowed to remain for a considerable time to remove the large amount of grease which invariably hangs about this class of work. To assist in the removal of this, the pieces are brushed over while in the potash tank ; it is important that the potash liquor be in an active condition that is, rich in the caustic alkali or it will fail to kill the grease, as it is termed, or convert it into soap. After being thus cleansed in the potash bath, the work is removed piece by piece and rinsed, after which it is briskly scoured, and, after again rinsing, is passed through the acid dip for an instant, again well rinsed, and put into the nickel tank. When all parts of the machine are nickeled they are handed to the finisher, who " limes " them ; that is, the backbone, fork, and other pieces, excepting the wheels, are polished and dollied with Sheffield lime at the lathe. The wheels, as before, are finished with lime, applied, by means of chamois-leather, by hand. The various parts are then readjusted, the machine carefully wiped all over, and it is then ready for the customer. Should the india-rubber tyre come off the wheel after being in the nickel bath, it may be replaced by fusing india-rubber cement upon the periphery of the wheel by heating over a gas-burner. While the cement is hot the tyre should be replaced in its position. Nickeling Sword Scabbards, &c. It not unfrequently occurs that a nickel-plater receives a sword and sheath with instruction to nickel the latter only. When such is the case, the sword should be with- 316 ELECTRO-DEPOSITION OF NICKEL. drawn and placed where it cannot become moistened by the steam from the potash tank or otherwise injured. To prepare the scabbard for plating, the thin laths of wood with which it is lined must first be removed, since if the sheath were placed in the nickel bath without doing so, these pieces of wood, by absorbing the nickel solution, would become so completely saturated that much difficulty would afterwards occur in drying them. "We have heard of instances in which this precaution has not been observed, and as a consequence the sword, after being sheathed for some time probably for some months was not only thickly coated with rust, but deeply corroded, owing possibly to voltaic action set up by the nickel solution absorbed by the wooden lining ; in one such instance the sword had become so firmly fixed in the scabbard, through the oxidation of its blade, that it was unsheathed with great difficulty, and when at last withdrawn it was thickly coated with rust. The strips of wood referred to must, therefore, in all cases be removed before the sheath is immersed in either of the liquids employed. To do this, remove the screw which unites the collar to the upper part of the sheath ; remove the collar, and with the blade of a knife loosen the strips of wood and withdraw them from the sheath, taking care to remove all of them. The two parts of the sheath and the screw must then be handed to the polisher, and when returned to the plating -shop they are first to be potashed, and after- wards scoured, passed through the acid dip, and after well rinsing put into the nickel bath, in which the scabbard should be slung horizon- tally, so as to get as uniform a deposit as possible. The collar and screw, slung upon separate wires, should then be placed in the bath, care being taken that the latter does not receive too heavy a coating, or some difficulty may arise in replacing it. To avoid this, the head of the screw only should be put into the bath. To prevent the nickel deposit from entering the screw-hole of the scabbard, a small plug of wood may be forced into the hole before the latter is put into the bath. When the several parts are sufficiently coated, which occupies about two hours, they are removed from the bath, rinsed in hot water, and well dried ; they are then sent to the finisher, after which any lime that may have got into the screw-hole must be removed with a brush ; the strips of wood and collar are then re- adjusted, the scabbard carefully wiped with a chamois -leather, and the sword replaced. Nickeling Harness Furniture, Bits, Spurs, &c. This class of work, when properly nickeled, may be considered one of the most use- ful applications of the nickel-plating art, but unfortunately as is also the case with many other articles a good deal of indifferent nickel- ing, the consequence, in a great measure, of unwholesome competi- tion, has appeared from time to time, which has had the effect of NICKELING HARNESS FURNITURE, ETC. 317 shaking the confidence of manufacturers who were at one time much disposed to encourage this branch of electro-deposition. That com- petition may be carried too far is evidenced by the extremely low prices which are asked for nickeling articles at the present time, as compared with, say, five years ago ; in many instances (if the work were done conscientiously) below the fair cost of polishing. When it is borne in mind that bits, spurs, stirrups, and all kinds of harness work are necessarily subjected to severe treatment in use, and that to nickel-plate such articles badly, for a temporary advantage, has a positive tendency, if not to close this market entirely against nickel- plating, at least to confine it solely to those who have a known repu- tation for doing their work properly, and can therefore be relied upon. We are led to make these remarks, en passant, because we have an earnest desire that nickel-plating should not lose its character for absolute usefulness for the temporary advantages of competition. We say temporary, because we know that much mischief has accrued to the art generally in consequence of work undertaken at prices that could not yield a profit being so badly nickel -plated, that some manufac- turers have ceased to avail themselves of this branch of industry except in cases of absolute necessity. In nickeling the class of work referred to, all the parts which are to be bright when finished must, as in all other cases, be previously well polished. Sometimes the articles are sent from the manufactory in this condition, but when such is not the case the pieces must be first handed to the polisher, and when returned to the plater they are to be potashed, scoured, and passed through the acid dip, and rinsed as be- fore, and then placed in the nickel vat, where they should remain (with an occasional shifting) for about an hour and a half, by which time, with a good dynamo, they will have acquired as thick a coating as may be given without fear of peeling. After removal from the bath and rinsing in hot water, the articles are placed in the finisher's hands, and when finished, the lime which lodges in the crevices should be brushed away and the articles then wiped with a chamois-leather and wrapped up. The brushing of work after finishing is too often neglected, and we have known of many complaints having been made by customers of the "filthy state" in which nickel-plated work has been received, owing to the lime falling out of tubes and hollows and from other parts of articles when they have been unpacked and examined on the counter. All work, after lime-finishing, should be well brushed, and wiped with a leather ; it does not occupy much time, and should be considered a necessary detail of the business. Nickeling Cast-iron Work. Articles of this class as kilting machines, for example are first potashed in the usual way, and after rinsing they are immersed in a pickle composed of half-a.cound of 318 ELECTRO-DEPOSITION OF NICK FT,. sulphuric acid to each gallon of water used to make up the bath. In this they are allowed to remain for about half -an -hour, when they are removed, well rinsed, and scoured : for this purpose the author prefers sand to pumice powder, from the fact that when the former is used the articles have a brighter or more lustrous appearance when nickeled than if pumice be employed, besides which sand is cheaper. It frequently occurs, in cast-ironwork, that numerous cavities, or " sand- holes," of greater or less magnitude, become visible after pickling and scouring the work, and since the nickel will probably refuse to enter these hollows which is generally the case it may be advisable in the first instance to give the article a coating of copper in an alkaline coppering bath, by which these cavities, if they are clean after sand- brushing, will become coppered with the rest of the article and the nickel will follow. Sometimes, however, the sand-holes are filled with flux or oxide of iron, in which case the former must be picked out with a hard steel point, and the hollow discoloured by oxide of iron should be scraped out with a small steel scraper. This being done, the article must be again sand-brushed and put into the coppering bath until coated all over with a slight film of copper. "We have seen large iron castings in which the sand-holes have been so large and deep that the workmen at the foundry have been compelled to plug them with lead. Such defects as these should be looked for by the plater, and if any of these leaden stoppings appear it will be undoubtedly advisable to coat the article with copper before nickeling it, otherwise the nickel will not firmly adhere to the leaden stoppings. We should in all cases prefer to give a coating of copper to cast-iron work in the alka- line bath, since the cast metal is a very indifferent conductor, and re- quires, when not coated with copper, a very strong current ; indeed, a few tolerably large pieces of cast iron uncoppered will often monopo- lise the whole of the current from a dynamo -electric machine, and thereby hinder the progress of the other work. Nickeling Chain Work. It sometimes happens that steel, iron, and brass chains of considerable length are required to be nickeled, in which case the object must be treated according to the di- rections given for the respective metals. A convenient method of slinging a chain in the nickel bath is shown in Fig. 115. A number of pieces of stout cop- per wire, of uniform length, Fig. 115. are cu j. .^hiie the chain is being scoured, and both ends of the wires are dipped in dipping acid for a moment, and then well rinsed. The wires are then turned up into EE-NICKELIXG OLD WORK. 31 9 the form of a hook at one end, and when the chain is ready for sling-- ing, the hooks are passed through the links one at a time and at equa distances apart, each portion being lowered into the bath and sus- pended by bending the end of the wire over the conducting rod, as in the figure ; in this way two men can immerse a chain of considerable length in a very few moments. After a short immersion, each hook may be shifted one link, to allow the wire mark to be nickeled, or the same link may be inverted, as preferred. Re-Nickeling Old Work. When goods which have been nickel- plated require to be re-nickeled, it is always better to first remove the old coating by means of a stripping solution, for the reason, as we have before remarked, that nickel will not adhere to a coating of the same metal. A stripping bath for nickel may be composed as follows : Oil of vitriol 16 pounds. Nitric acid 4 , Water 2 quarts. Add the oil of vitriol to the water (not the reverse, which it is danger- ous to do) gradually, and when the mixture has cooled down add the nitric acid, and stir the mixture with a glass rod. When cold, it is ready for use. The articles to be stripped should be attached to a piece of stout brass or copper wire and placed in the stripping liquid, and after a few moments they should be lifted by the wire and examined. If the articles are of a cheap class of work, the small amount of nickel upon them may become dissolved off in less than half a minute : this is generally the case with American, French, and German goods. The better qualities of English nickel-plating will sometimes occupy many minutes before the whole of the nickel will come off. This great difference in the thickness of the nickel-plating necessitates much caution and judgment on the part of the workman, for if he were to treat all classes of work alike, the metal of which the thinly-coated articles are made would become severely acted upon if left in the stripping bath while work of a better class was being de- nickeled, as we may term it. The operation of stripping should be conducted in the open air, or in a fire-place with good draught, so that the acid fumes may escape through the chimney. From the moment the articles are immersed in the stripping bath they should be constantly watched, being raised out of the bath frequently to see how the operation progresses, and they should not on any account be allowed to remain in the liquid one moment after the nickel has been dissolved from the surface, but should be immediately removed and plunged into cold water. On the other hand care must be taken to remove all the nickel, for if patches of this metal be left in parts it will give the polisher some trouble to remove it,, owing to the 32O ELECTRO-DEPOSITION OP NICKEL. hardness of nickel as compared with the brass or copper of which the article may be composed. When the stripping of brass work has been properly conducted, the surface of the stripped article presents a smooth and bright surface, but little affected by the acid bath. Nickel may be removed 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 ; or a bath may be made with dilute sulphuric or hydrochloric acid ; the stripping solution, however, when in good condition and used with care, is not only quick in its effect, but comparatively harmless to the underlying metal, if proper judgment and care have been exercised. Work which is in any way greasy should be steeped in the potash bath before stripping. After the work has been stripped and thoroughly well rinsed, it should be dipped hi boiling water, and then laid aside to dry sponta- neously ; it is next sent to the polishing room, where it must be polished and finished in the same way as new work, and afterwards treated in the nickeling room with as much care and in the same way as new goods. Nickel-facing Electrotypes. In printing from electrotypes with coloured inks, but more especially with vermilion inks, which are prepared from a mercurial pigment, not only is the surface of the electrotype injuriously affected by the mercury forming an amalgam with the copper, but the colours are also seriously impaired by the de- composition which is involved. To avoid this it is frequently the practice to give electrotypes to be used for such purposes a coating of nickel, which effectually protects the copper from injury. In some printing establishments a nickel bath is kept specially for this purpose. The electrotypes, after being backed up and prepared for mounting in the usual way, are lightly brushed over with a ley of potash, and after well rinsing are suspended in the nickel bath for about an hour or so, by which time they generally receive a sufficient coating of nickel. Great care should be taken, however, not to employ too strong a current, lest the lower corners of the electrotype should be- come burnt, as it is called, by which a rough surface is produced, from which the ink, in subsequent printing, would fail to deliver properly ; this defect, however, is readily avoided with care, and by occasionally reversing the position of the plate while in the bath. For nickel-facing electros of moderate dimensions, an oval stone- ware pan, capable of holding about ten to fifteen gallons of solution, may be used. The nickeling bath should consist of about three- quarters of a pound of good nickel salts (double sulphate of nickel and ammonia) to each gallon of water. The salts should be dissolved in hot water and filtered into the containing vessel through a piece of NICKELING PRINTING ROLLERS. 321 unbleached calico. The anodes may consist of two plates of rolled nickel, each about 12 inches long by 6 inches wide, these being suspended in the bath by hooks from a brass rod laid across the vat. A Bunsen battery of about one gallon capacity will give a current sufficient for nickeling electros of moderate size. The positive elec- trode (the wire proceeding from the carbon of the battery) is to be connected to the brass rod supporting the anodes, and a similar rod, connected to the zinc of the battery, is to be laid across the vat in readiness to receive the prepared electros to be nickeled. The suspend- ing rods and all binding screw connections must be kept perfectly clean. When putting an electro in the bath, care must be taken to expose its face to the anodes, otherwise little or no deposit will take place upon this surface. If desired, a second row of anodes and an additional negative rod for supporting electrotypes may be employed, in which case the electros must be all suspended back to back, so as to face the anodes. An additional battery will be required. The faces of the electros may be placed within 3 or 4 inches of the anodes, and each should be supported by two wires passed through the nail holes in the backing metal which are nearest the corners. Nickeling Wire Gauze. Messrs. Louis Lang & Son obtained a patent in 1881 for a method of nickeling wire gauze, or wire to be woven into gauze, more especially for the purposes of paper manufac- ture. These wires, which are generally of copper or brass, are liable to be attacked by the small quantities of chlorine which generally re- main 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 re -wound on to another bobbin, and re -immersed in the nickel bath as before, so as to coat such surfaces as were in contact with each other and with the first bob- bin. To deposit nickel on the woven tissue, 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 Printing Rollers. Mr. Appleton obtained several patents in 1883 for coating with nickel the engraved rollers used for printing and embossing cotton and other woven fabrics, to protect them from the chemical action of the various colours and chemical matters used in calico printing, &c., by which the copper rollers be- come deteriorated. Nickel-plated rollers, moreover, presenting a much harder surface than copper, are far move durable. The rollers are first X 322 ELECTRO-DEPOSITION OP NICKEL. engraved as usual, after which they are immersed in any ordinary nickel bath. The inventor finds it advantageous, in order to secure a uniform coating of nickel, to "vibrate, agitate, oscillate, or rotate the roller continuously, or intermittently," while the deposition is taking place. He has found, however, some difficulty in obtaining a firm deposit, " owing to the formation of gas bubbles upon the surface of the roller, and the difficulty in dislodging them. To obviate this he finds it advantageous to employ " a brush, which is in contact with the roller during the plating operation, the roller being rotated con- tinuously, or intermittently, as preferred." The brush is suspended from the cathode rod, so that the bristles may touch the surface of the roller, and thus remove any adhering bubbles. He prefers a brush made with vegetable fibre or spun glass, or other substance not liable to be acted upon by the solution. Nickeling Notes. I . It may be taken as a rule that only a limited quantity of nickel can be deposited upon either brass, copper, steel, or iron ; if this limited amount of metal be exceeded the deposited metal will assuredly separate from the underlying metal. It has also been found in practice that a greater thickness of nickel can be deposited upon brass and copper without spontaneously peeling off than upon steel or iron. Since nickel, however, is an exceedingly hard metal, and will bear a considerable amount of friction, a very thin coating indeed is all that is necessary for most of the articles to which nickel- plating is applied. "We may, however, state that too much advantage has been taken of this fact, for many articles of American and conti- nental manufacture enter the market upon which a mere film of nickel has been deposited, and consequently they soon become unsightly from the rapidity with which the flimsy coating vanishes with even moderate wear. As a rule, the nickel-platers of this country deposit a very fair, and in many instances a very generous, coating of nickel upon their work, which has caused the home nickel-plating industry to hold a high position both as regards fhejinish of the work and its durability. It will be a thing to be regretted if price -competition should cause this useful branch of electro -deposition to become degraded by coating well-manufactured articles with a mere skin of nickel ! 2. Nickeling Steel Articles. When small steel work, such as purse mounts, book-clasps, &c. , have to be nickeled, it is better first to suspend larger articles of brass or copper upon one end of the conducting rod, and to reserve the other end of the rod for the steel articles, or to sling them between the larger pieces of work ; when it is not convenient to do this, one of the anodes should be slung from the end of the rod farthest from the battery, as a cathode, so as to take up a portion of the current. When steel articles are placed in the bath they should become " struck," as it is termed that is, receive a slight coating of NICKELING NOTES. 323 nickel almost immediately after immersion, but from that moment the deposition must be allowed to progress slowly, otherwise the work will surely strip, and this it will sometimes do even while in the bath : we have known steel work peel, when removed from the bath, by simply striking it gently against a hard substance. It is also of much importance that steel work should be placed in the bath directly after it has been passed through the hydrochloric acid pickle and rinsed, since even a few moments' exposure to the air especially if there be any acid fumes given off by the batteries will cause a film of oxide to form on the surface and render the deposit liable to strip. 3. Rinsing the Articles. It will be readily understood that if articles are imperfectly rinsed after dipping, the acid or cyanide, as the case may be, which may still hang about them must be a source of injury to the nickel bath. It is therefore advisable not to depend upon one rinsing water only, but to give the work a second rinsing in perfectly clean water. It is very commonly the practice to give the final rinsing in one division of the scouring tray, the water of which can be readily changed by simply removing the plug and turning on the tap when it is replaced. 4. Lime wed in Finishing Nickel-plated Work. The lime used for finishing work which has been nickel-plated is generally obtained from Sheffield, and since this substance becomes absolutely useless after it has been exposed to the air by which it attracts carbonic acid and falls to an impalpable powder possessing little or no polishing effect upon nickel it must be preserved in air-tight vessels. For this purpose olive jars, or large tin canisters such as are used by grocers, answer well. Small quantities may be preserved in stone jars, covered with a well-fitting bung. The general practice is to take a lump of lime from the jar, cover the vessel immediately, and after breaking off a sufficient supply from the selected lump, to return it to the jar, which is again securely covered. The fragments of lime are then powdered in a mortar, and after sifting through a fine sieve or muslin bag, the powder is handed to the finisher, who informs the assistant (generally a boy) a short time before he requires a fresh supply of the powdered lime. By this arrangement the lime then always gets into the hand of the finisher in good condition for his purpose. 5. Nickeling Dental Work. One of the most successful purposes to which nickeling has been applied for many years, is in coating den- tist's tools, including forceps, excavators, and other implements used in dental practice. These articles, which are made from fine steel, are usually sent by the makers to the nickel-plater in a highly- finished condition, and therefore require but a moderate amount of labour in the plating and polishing shops to turn them out of hand. 324 ELECTRO-DEPOSITION OF NICKEL. To prepare this class of work for the bath, the pieces are first wired, after which they are suspended in the potash bath for a short time, or until required to be scoured. They are now removed, a few at a time, and rinsed, after which they are taken to the scouring bench, where they are brushed over with pumice and water ; each piece, after rinsing, is dipped for a moment in the hydrochloric acid dip, again rinsed, and immediately suspended in the vat. To prevent these small pieces from receiving the deposit too quickly and thus becoming " burnt " they are usually suspended between articles of a larger size which are already in the bath. "When battery power is used for coat- ing articles of this class (with larger work), from two to three hours' immersion in the bath will be required to obtain a fair coating ; with a dynamo about half that period will be sufficient. Dental forceps require a somewhat longer immersion than the smaller tools. When the work is sufficiently nickeled, it is removed from the bath, rinsed in hot water, and sent into the polishing room to be lime -finished, after which it should be thoroughly well brushed to remove the lime, especially from the interstices. Some packers, or warehousemen, are apt to be rather careless in this respect, and are satisfied with giving nickel-plated and finished work a slight rub up with a leather, so that when the articles are received by the customer, the first thing that attracts his attention, when unpacking the work, is the appearance of a quantity of dirty lime which has fallen from the goods after they were wrapped in paper. This negligence has often been the cause of complaint, and since it can be so readily avoided by a little extra care, this should always be impressed upon the packer of finished work. 6. Recovery of Nickel from Old Solutions. This is most readily effected by following Mr. Unwin's ingenious method of preparing the double salts of nickel and ammonia, namely, by taking advantage of the insolubility of the double sulphate of nickel and ammonia in con- centrated solutions of the sulphate of ammonia. To throw down the double salts from an old solution, or from one which fails to yield a good deposit, prepare a saturated solution of sulphate of ammonia, and add this, with constant stirring, to the nickel solution, when, after a little while, a granular deposit of a green colour will form, which will increase in bulk upon fresh additions of the sulphate being given. The effect is not immediate, on adding the sulphate of ammonia solu- tion, but after a time the green deposit will begin to show itself, and when a sufficient quantity of the ammonia salt has been added, the supernatant liquor will become colourless, when the operation is com- plete. The additions of sulphate of ammonia should be gradually made, and the mixture allowed to rest occasionally, after well stirring, to ascertain if the green colour of the nickel solution-has disappeared. The clear liquor is to be poured off the granular deposit which is NICKELING NOTES. 325 pure double sulphate of nickel and ammonia and this should be allowed to drain thoroughly. It may afterwards be dissolved in water and used as a nickel-plating bath. The solution of sulphate of ammonia may be evaporated, and the salt allowed to crystallise ; and if the crystals are afterwards re -dissolved and again crystallised, the resulting product will be sufficiently pure for future use. 7. "Doctoring" This term is applied to a system of patching up an article which has been ' ' cut through, ' ' or rendered bare, in the pro- cess of lime-finishing, and it is adopted to avoid the necessity of re -nickeling the whole article, which would often entail considerable loss to the plater. When the faulty article is sent back from the polishing room the first thing to do is to arrange the " doctor," which is performed as follows : A piece of stout copper wire is bent in the form of a hook at each end ; a piece of plate nickel, about one and a half inch square (or a fragment of nickel anode) is now bound firmly to one of the hooks with a piece of twine ; the lump of nickel is then wrapped in several folds of calico, or a single fold of chamois -leather. The second hook is now to be 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 to be dipped in the nickel bath, applied to the defec- tive spot (which should be first lightly scoured with pumice and water) and allowed to rest upon it for a few moments, then dipped again and reapplied. 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 to enable the finisher to apply the " dolly " to the re- nickeled spot, and thus render it as bright as the rest of the article. When the operation is skilfully performed, both by the plater and finisher, no trace of the patch will be observable. 8. Common Salt in Nickel Solutions. Owing to the inferior conductivity of nickel baths, various attempts had been made to improve the con- ducting power of these solutions by the addition of other substances, but the most successful of these, of French origin, was the introduc- tion of chloride of sodium (common salt), which is a very good con- ductor of electricity. The addition of this substance was subsequently adopted by a well-known London firm, the character of whose nickel- plated work was much admired for its whiteness as compared with some other specimens, of a more or less yellow tone, which appeared in the market at that time. The advantages to be derived from the addition of common salt to nickel solutions have been very clearly demonstrated by M. Desmur, who, in a communication to the author, in June, 1880, made the following interesting statement,* which he * Electro-Metallurgy, Practically Treated. By Alexander Watt. Eighth edition, p. 229. 326 ELECTRO-DEPOSITION OF NICKEL. deems it advisable to reproduce in this place from its importance to those who follow the nickel-plating industry : 9. Augmentation of the Conductivity of Nickel Baths M. Desmur says : " The resistance of nickel baths as they are usually prepared, i.e. by dissolving double sulphate of nickel and ammonia in water, is very great. I would advise persons engaged in the trade to intro- duce into their baths ten per cent, of chloride of sodium (common salt). I have observed, by means of a rheostat, that the addition of this salt augments the conductivity by thirty per cent., and that the deposit is much whiter and obtained under better conditions. The diminution of resistance is in proportion to the quantity of chloride of sodium added, for the conducting power of a solution of this salt increases with its degree of concentration up to the point of saturation. I mention this fact because it is not the case with all saline solutions. For example, saturated solutions of nitrate of copper, or sulphate of zinc, have the same conductive power as more diluted solutions, be- cause the conductibility of these solutions increases as the degree of concentration reaches its maximum, and diminishes as the concen- tration increases." In our own experience we have observed that not only is the nickel deposit rendered much whiter by the addition of chloride of sodium, but it is also tougher and more reguline ; indeed, we have known a stout deposit of nickel upon sheet brass or copper to allow the metal to be bent from its corners and flattened without the least evidence of separation or even cracking a condition of deposit not often obtained in plain double sulphate solutions. 10. Nickeling Small Articles by Dynamo-electricity. Small steel pieces, such as railway keys, for example, should not be kept in the bath longer than an hour, or an hour and a half at the most. About twice this period will be necessary when battery power is employed. Brass and copper work, as a rule, may remain in the bath about double the length of time required for steel work. 1 1 . Nickeling Small Screws When a large number of small screws have to be nickeled, they may be placed in a brass wire-gauze basket, made by turning up a square piece of wire -gauze in the form of a tray, and overlapping the corners, which must then be hammered flat and made secure by soldering. A piece of stout copper wire, bent in the form of a bow and flattened at each end, is then to be soldered to the centre of each side of the tray, forming a handle, by which it may be sus- pended in the bath by the negative wire of the battery or other source of electric power. The screws, having been properly cleaned, are placed in the basket, which is then immersed in the bath, and while deposition is taking place the basket must be gently shaken occa- sionally to allow the parts in contact to become coated : this is espe- NICKELING NOTES. 327 cially necessary during the first few moments after immersion. When nickeling such articles in the wire basket, they should be placed in a single layer, and not piled up one above another, since nickel has a strong objection to deposit round the corner. It is better, however, to sling screws by thin copper wire than to use a basket ; and though the operation is a rather tedious one, a smart lad can generally ' < wire " screws, after a little practice, with sufficient speed for ordinary de- mands. The simple method of wiring screws before described will be found very useful, and if the necessary twist is firmly given there need be no fear of the screws shifting ; the wire used for this purpose should never be used a second time without stripping the nickel from its surface and passing it through a clear fire to anneal it. When nickeling screws, it is best to sling them between other work of a larger size, otherwise they are liable to become burnt, which will necessitate stripping off the deposited nickel or facing them upon an emery wheel. 1 2 . Dead Nickel-plating. Certain classes of work, as ship deck lamps, kilting machines, and various cast-iron articles, are generally required to be left dead that is, just as they come out of the nickel bath. All such work, when removed from the bath, should be at once rinsed in very hot and perfectly clean water. Care should be taken not to allow the work to be touched by the fingers at any part that catches the eye, since this handling invariably leaves an unsightly stain. Cast-iron work, when properly nickel-plated, presents a very pleasing appearance, which should not be marred by finger-r ks before it reaches the hands of the customer. 13. "Dry" Nickel-plating- This method, which is of American origin, has sometimes been adopted in this country for umbrella mounts and other small work, but it is only applicable to very cheap work, upon which the. quantity of nickel is of secondary importance. Work of this character is generally dollied with a " composition " consisting of crocus (oxide of iron) mixed up into the form of a hard solid mass with tallow. The workman takes a lump of the composition, which he presses against the revolving dolly until it has acquired a small amount of the composition upon its folds (as in lime -finishing). He now holds the piece of work to the dolly, which quickly becomes brightened. When a sufficient number of pieces have been prepared hi this way, they are suspended by any suitable means and at once placed in the bath, and so soon as they have become sufficiently coated for this class of work, that is in about half-an-hour or so, the articles are removed, rinsed, and dried, and after a slight dollying are ready for market. A convenient arrangement for suspending umbrella mounts, and articles of a like description, is shown in Fig. 116. 14. Removing Nickel from Suspending Appliances. When wire- 3*8 ELECTRO-DEPOSITION OF NICKEL. gauze trays, wire suspenders, and other contrirances by which articles havo been supported in the bath have been used many times, they [] : Fig. i i 6. naturally become thickly coated with nickel, and since this metal when deposited upon itself has no adhesion, the various layers of nickel which the tray, &c., have received from time to time generally curl up and break off with the slightest touch, and the fragments are liable not only to fall into the bath, but upon any work which may be in the solution at the time. It is better, therefore, to remove the nickel from these appliances, either by means of a stripping solution or by connecting them to the positive electrode of a battery and dissolving the metal off by electrolysis, for which purpose a small bath may be specially kept. 15. Recovery of Dropped Articles from the Bath. When an article is accidentally dropped into the nickel vat, the workman should have at hand a ready means of recovering it without resorting to the Fig 117 unhealthy practice of plunging his bare arm into the solution. Many contrivances have been adopted for this purpose, amongst which may be mentioned an instrument of which a sketch is shown in Fig. 117. This simply consists of a per- NICKELING NOTES. 329 forated iron plate, fitted with a suitable handle, which may be con- veniently attached by means of a socket brazed on to the perforated plate. If this tool, or lift, be gently lowered into the bath, in the direction in which the article is supposed to lie, and carefully moved about, so as not to disturb the sediment more than can be avoided, the lost article will probably soon come in contact with the lift, which should then be guided so as to draw the article to the side or end of the bath, when it may be shovelled on to the perforated plate and gradually lifted to the surface of the bath and taken off the plate, and the instrument hung up in its proper place ready for use another time. When small steel or iron articles fall into the bath, they may be recovered by means of a horse -shoe magnet. For this purpose a tolerably large magnet, having a cord attached to its centre and allowing the poles to hang downward, may be employed, and if allowed to drag along the bottom of the vat slowly, so as to avoid disturbing the sediment as much as possible, the lost article may generally be recovered and brought to the surface, even when the bath is full of work, without stirring up the sediment to any serious extent. When the recovery of the dropped pieces is not of any immediate consequence, this is better left till the evening, after the last batch of work has been removed. 1 6. Rolled Nickel Anodes. The cost of a nickel-plating outfit, when cast anodes are employed, is in this item alone excessively heavy, since in many cases such anodes, for large operations, frequently weigh more than a quarter of a hundredweight each ; and when it is borne in mind that for a 25O-gallon bath from sixteen to twenty-four anodes would be required except when a dynamo or magneto -electric machine is employed, when about half that number would be sufficient it will be at once seen that the aggregate weight of metal would be consider- able. Since rotted nickel anodes can now be obtained of almost any required thinness, from one -fourth to one -eighth of the quantity of metal only would be required to that of the cast metal. It is a common fault with cast nickel anodes that after they have been in use a short time they become soft and flabby while in the depositing vat, and will even fall to pieces with the slightest handling and become deposited not in the electrolytic sense at the bottom of the vat. It is not an uncommon circumstance, moreover, to find a considerable per- centage of loose carbon graphite interspersed with the badly-cast nickel, and which, of course, if paid for as nickel, entails a loss upon the consumer. We have seen samples of such anodes containing nearly thirty per cent, of graphite, which could easily be scooped out with a teaspoon ! Some very good specimens of cast nickel, however, enter the market in which neither of the above faults are to be found ; indeed, we have examined samples containing 99 per cent, of nickel, 33 ELECTBO-DEPOSITION OF NICKEL. which for all practical purposes may be said to be pure. We should, in any case, give our preference to rolled nickel anodes ; and for the following reasons : They are less costly ; they become more uniformly dissolved in the bath ; they are generally more pure ; they do not soften in the solution, and are less cumbersome to handle than cast anodes, which is an advantage when these require to be shifted, as in plating mullers and other large pieces. 17. Nickeling Cast Brass Work. It sometimes occurs that work of this description is full of sand-holes ; when such is the case, the polisher should receive instructions to obliterate these as far as possible, for nothing looks more unsightly in nickel-plated and finished articles than these objectionably cavities. It not unfre- quently happens, however, that some sand-holes are too deep to be erased by the polishing process, with any amount of labour, while sometimes, in his endeavour to obliterate these defects the polisher finds that they extend in magnitude, and are found to enter deep into the body of the work. In such cases all attempts to eradicate them will be futile, and must therefore be abandoned. Polishers and finishers accustomed to prepare work for" nickel-plating are fully aware of the importance of a fair face on the work, and they generally do their best to meet the requirements of the nickeling process, and many of them are exceedingly careful to prepare the work so that, when nickeled and finished, it shall look creditable. CHAPTER XXIV. DEPOSITION AND ELECTRO -DEPOSITION OF TIN. Deposition by Simple Immersion. Tinning Iron Articles by Simple Immer- sion. Tinning Zinc by Simple Immersion. Tinning by Contact with Zinc. Roseleur's Tinning Solutions. Deposition of Tin by Single Cell Process. Dr. Hillier's Method of Tinning Metals. Heeren's Method of Tinning Iron Wire. Electro-deposition of Tin. Roseleur's Solutions. Fearn's Process. Steele's Process. Electro-tinning Sheet Iron. Spence's Process. Recovery of Tin from Tin Scrap by Electrolysis. THERE are three different methods of coating brass and other metals with tin in what is termed the wet way, in contradistinction to the ordinary method of tinning by immersion in a bath of molten metal. By two of these methods a beautifully white film of tin is deposited, but not of sufficient thickness to be of a durable character. By the third method, a deposit of any required thickness may be obtained, although not with the same degree of facility as is the case with gold, silver, and copper. Deposition by Simple Immersion, or "Dipping." For this pur- pose, a saturated solution of cream of tartar is made with boiling water : in this solution small brass or copper articles, such as brass pins, for example, are placed between sheets of grain tin, and the liquid is boiled until the desired result is obtained a beautifully white coating of tin upon the brass or copper surfaces. Ordinary brass pins are coated in this way. Some persons add a little chloride of tin to the bath to facilitate the whitening, as it is termed. The articles are afterwards washed in clean water, and brightened by being shaken in a leathern bag with bran, or revolved in a barrel. Tinning Iron Articles by Simple Immersion. A solution is first made by dissolving, with the aid of heat, in an enamelled pan Protochloride of tin (fused) ... zi grammes. Ammonia alum 75 Water 5 litres.* * Tables of French weights and measures are given at the end of the volume. 332 DEPOSITION AND ELECTRO-DEPOSITION OF TIN. The chloride of tin (which may be obtained at the drysalters) is readily made by dissolving grain tin in hydrochloric acid, with the aid of heat, care being taken to have an excess of the metal in the dissolving flask. When the bubbles of hydrogen gas which are evolved cease to be given off the action is complete. If the solution be evaporated at a gentle heat until a pellicle forms on the surface, and the vessel then set aside to cool, needle-like crystals are obtained, which may be separated from the "mother liquor" by tilting the evaporating dish over a second vessel of the same kind. When all the liquor has thoroughly drained, it should in its turn be again evaporated, when a fresh crop of crystals will be obtained. The crystals should, before weighing, be gently dried over a sand bath. The ammonia alum is an article of commerce, and is composed of ammonia, 3-75 ; alumina, 11*34; sulphuric acid, 35*29; and water, 49*62, in 100 parts. It may be prepared by adding crude sulphate of ammonia to a solution of sulphate of alumina. When the solution of tin and alum has been brought to a boil, the iron articles, after being well cleaned and rinsed in water, are to be immersed in the liquid, when they quickly become coated with a deli- cately white film of a dead or matted appearance, which may be rendered bright by means of bran in a revolving cask, or in a leathern bag shaken by two persons, each holding one end of the bag. The scratch-brush is also much used for this purpose. To keep up the strength of the tinning or whitening bath small quantities of the fused chloride of tin are added from time to time. Articles which are to receive a more substantial coating of tin by the separate battery may have a preliminary coating of tin in this way. Tinning Zinc by Simple Immersion. To make a bath for tinning zinc by the dipping method, the ordinary alums of commerce (potash and soda alums) may be used. In other respects, the solution is prepared and used in the same way as the above ; and it may be stated that the proportions of the tin salt and ammonia in water need not of necessity be very exact, since the solution, after once being used, becomes constantly weakened in its proportion of metal, still giving very good results, though somewhat slower than at first. For coating articles made of brass, copper, or bronze, a boiling solu- tion of peroxide of tin in caustic potash makes a very good bath, yielding a coating of extreme whiteness. A still more simple solution may be made by boiling grain tin, which should first be granulated, in a moderately strong solution of caustic potash, which in time will dissolve sufficient tin to form a very good whitening solution. Tinning by Contact with Zinc. Deposits of tin upon brass, copper, iron, or steel may easily be obtained from either of the fol- lowing solutions by placing the articles, while in the hot tinning EOSELEUK'S TINNING SOLUTIONS. 333 bath, in contact with fragments of clean zinc, or with granulated zinc. To granulate zinc, tin, or other metals, have at hand a deep jar, or wooden bucket, nearly filled with cold water, upon the surface of which spread a few pieces of chopped straw or twigs of birch. When the metal is melted, let an assistant stir the water briskly in one direction only, then, holding the ladle or crucible containing the molten metal high up above the moving water, pour out gradually, shifting the position of the ladle somewhat, so that the metal may not all flow down upon the same part of the vessel's bottom. When all the metal is poured out, the water is to be run off, and the granulated metal collected and dried. It should then be put into a wide-mouthed bottle or covered jar until required for use. Roseleur's Tinning Solutions. Roseleur recommends either of the two following solutions for tinning by contact with zinc : I . Equal weights of distilled water, chloride of tin, and cream of tartar are taken. The tin salt is dissolved in one-third of the cold water ; the remaining quantity of water is then to be heated, and the cream of tartar dissolved in it ; the two solutions are now to be mixed and well stirred. The mixture is clear, and has an acid reaction. 2. Six parts of crystals of chloride of tin, or 4 parts of the fused salt, and 60 parts of pyrophosphate of potassium or sodium are dissolved in 3,000 parts of distilled water, the mixture leing well stirred ; this also forms a clear solution. Both the above solutions are to be used hot, and kept constantly in motion. The articles to be tinned are immersed in contact with fragments of zinc, the entire surface of which should be equal to about one -thirtieth of that of the articles treated. In from one to three hours the required deposit is obtained. To keep up the strength of the bath equal weights of fused chloride of tin and pyro- phosphate are added from time to time. Eoseleur gives the preference to this latter solution if the pyrophosphate is of good quality. He also prefers to use coils of zinc instead of fragments of the metal, as being less liable to cause markings on the articles than the latter, which expose a greater number of points. It is evident from this that granulated zinc should not be used with these solutions, since metal in this form would exhibit an infinite number of points for contact. For tinning small articles, such as nails, pins, &c., these are placed in layers upon perforated zinc plates or trays, which allow of the circulation of the liquid ; the edges of the plates are turned up to keep the articles from falling off the zinc surfaces. These plates are placed upon numbered supports, in order that they may be removed from the bath in the inverse order in which they were immersed. The plates are scraped clean each time before being used, in order that a perfect metallic contact may be insured between the plates and the articles to be tinned. During the tinning the small articles are occasionally 334 DEPOSITION AND ELECTRO-DEPOSITION OP TIN. stirred with a three-pronged iron fork, to change the points of contact. After the articles have been in the bath from one to three hours an addition of equal parts of pyrophosphate and fused chloride is made, and the articles are then subjected to a second immersion for at least two hours, by which they receive a good deposit. Large articles (as culinary utensils, &c.) coated in the above solution are scratch- brushed after the first and second immersions. The final operations consist in rinsing the articles, and then drying them in warm sawdust In reference to the working of the above solutions, Roseleur says : "If we find that the tin deposit is grey and dull, although abundant, we prepare [? strengthen] once or twice with the acid crystallised protochloride of tin. With a very white deposit, but blistered, and without adherence or thickness, we replace the acid salt, by the fused one. In this latter case we may also diminish the proportion of tin salt, and increase that of the pyrophosphate." For tinning zinc in a pyrophosphate bath, the following proportions are recommended : Protochloride of tin (fused) . . i kilogramme. Pyrophosphate of soda ... . 5 kilogrammes. Distilled water .... 300 litres. Deposition of Tin by Single Cell Process. Weil makes a tinning solution by dissolving a salt of tin in a strong solution of caustic potash or soda ; a porous cell nearly filled with the caustic alkali (with- out the tin salt), and in this metallic zinc, with a conducting wire attached, is placed, the end of the wire being put in contact with the articles to be tinned. The solution of zinc formed in the porous cell during the action is revived by precipitating the zinc with sulphide of sodium. Dr. miller's Method of Tinning Metals. A solution is pre- pared with I part chloride of tin dissolved in 20 parts of water; to this is added a solution composed of 2 parts caustic soda and 20 parts of water ; the mixture being afterwards heated. The articles to be tinned are placed upon a perforated plate of block tin and kept in a state of agitation, with a rod of zinc, until they are sufficiently coated. Heeren's Method of Tinning Iron "Wire. This consists in first cleaning the wire in a hydrochloric acid bath in which a piece of zinc is suspended. The wire thus cleaned is then put in contact with a plate of zinc in a bath composed as follows : Tartaric acid 2 parts. Water 100 To this is added, 3 parts of each, chloride of tin and soda. After remaining in the above bath about two hours, the wire is brightened by drawing it through a hole in a steel plate. ELECTRO-DEPOSITION OF TIN. 335 Electro-deposition of Tin. Although the deposition of tin by simple dipping, or by contact with zinc, is exceedingly useful for small articles, and may be pursued by persons totally ignorant of electro -deposition, the deposition of this metal by the direct current is far more reliable when deposits of considerable thickness are desired, besides being applicable to articles of large dimensions. There have been many different processes recommended some of which have been patented for the electro -deposition of this metal, and several of these have been worked upon a tolerably extensive scale. For many purposes, this exceedingly pretty metal, when properly deposited by electrolysis, is very useful, but more especially for coating the insides of cast-iron culinary vessels, copper preserving pans, and articles of a similar description. There is one drawback connected with the electro - deposition of this metal, however, which stands much in the way of its practical usefulness, and renders its deposition by separate current more costly than would otherwise be the case, namely, that the anodes do not become dissolved in the bath in the same ratio as the deposit upon the cathode, consequently the strength of the bath requires to be kept up by constant additions of some salt of the metal to the solu- tion while deposition is taking place. If this were not done, the bath would soon become exhausted, and cease to work altogether. To over- come this difficulty, and to keep up a uniform condition of the bath, the author pro- posed in his former work * the following method : Arrange above the depositing tank a stone vessel, capable of receiv- ing a tap (Fig. 1 1 8) ; to this connect a vulcanised india- rubber tube, reaching nearly to the surface of the solution. Let this jar be nearly filled with concentrated solution of the tin salt employed, made by dissolving the salt in a por- tion of the main solution. Fig. 1 1 8. When the bath is being worked, let the tap be turned slightly, so that the concentrated solution may drip or flow into the depositing bath. When the stone vessel has become empty, or nearly so, a fresh concentrated solution should be made, using the liquor from the bath to a certain extent in lieu of water, so as not to increase the bulk of Electro-Metallurgy." Eighth edition, p. 241. 336 DEPOSITION AND ELECTRO-DEPOSITION OF TIN. the bath more than is absolutely necessary. By this method several advantages are gained (i) By using the weakened bath each time to make the concentrated solution, there will be but trifling addi- tion to the bulk of the solution ; (2) By allowing the concentrated solution to continually enter the bath while deposition is taking place, there will be no necessity to disturb the bath by stirring in a larger quantity of the solution all at one time. In cases in which it is necessary to make additions of two separate substances, these may be introduced by employing two tapped vessels instead of one. Roseleur's Solution. The bath which this author recommends aa possessing all the conditions desired by the operator, is composed of: Protochloride of tin (in crystals) . . 600 grammes. Pyrophosphate of soda or potassa . . 5 kilogrammes. Distilled or rain water . ". ." . 500 litres. Instead of employing crystals of the tin salt, the fused substance in to be preferred, 500 grammes of which take the place of the former. In making up the bath, the water is put into a tank lined with anodes of sheet tin, united together, and put in connection with the positive electrode of the battery or other source of electricity. The pyro- phosphate salt is then put into the tank, and the liquid stirred until this is dissolved. The protochloride is plaeed in a copper sieve, and this half immersed in the solution. A milky-white precipitate is at once formed, which becomes dissolved by agitation. When the liquid has become clear and colourless, or slightly yellow, the bath is ready for use. The cleaned articles are now to be suspended from the negative conducting rods as usual. " The anodes," says Roseleur, " are not sufficient to keep the bath saturated ; and when the deposit takes place slowly, we add small por- tions of equal weights of tin salt and pyrophosphate. The solution of these salts should always "be made with the aid of the sieve, for if fragments of the protochloride of tin were to fall on the bottom of the bath they would become covered with a slowly soluble crust, pre- venting their solution." It is stated that any metal may be coated in this solution with equal facility, and that a good protective coating may be obtained with it, while the metal has a dead white lustre resembling that of silvsr, which may be rendered bright either by scratch-brushing or by burnishing. An intense current is necessary in working this solution. Fearn's Process. This process, for which a patent was granted in 1873, includes four different solutions, which may be thus briefly described : No. I . A solution of chloride of tin (containing but little free acid) is first prepared, containing 3 ounces of metallic tin per STEELE'S PROCESS. 337 gallon; 30 pounds of caustic potash are dissolved in 20 gallons of water ; 30 pounds of cyanide of potassium in 20 gallons of water ; and 30 pounds of pyrophosphate of soda in 60 gallons of water. 200 ounces (by measure) of the tin solution are poured slowly, stirring with a glass rod, into the 20 gallons of potash solution, when a precipitate is formed, which quickly redissolves ; into this solution is poured first all the cyanide solution, then all the pyrophosphate, and the mixture well stirred. No. 2. 56 pounds of sal-ammoniac are dissolved in 60 gallons of water ; 20 pounds of pyrophosphate of soda in 40 gallons of water ; into the latter is poured 100 ounces by measure of the chloride of tin solution, and the mixture well stirred, when the pre- cipitate formed redissolves as before. Lastly, the sal-ammoniac solu- tion is added, and the whole well stirred together. No. 3. 150 pounds of sal-ammoniac are dissolved in 100 gallons of water ; into this 200 ounces by measure of the tin solution are poured, and well stirred in. No. 4. To make this solution, 400 ounces of tartrate of potash are dissolved in 50 gallons of water; 1,200 ounces of solid caustic potash in 50 gallons of water ; 600 ounces by measure of the tin solu- tion are then added slowly, with stirring, to the tartrate solution ; the caustic potash solution is next added, the stirring being kept up until the precipitate which forms has become entirely redissolved. In using the above solutions, No. I is to be worked at a temperature of 70 Fahr., with a current from two Bunsen batteries; No. 2 is used at from 100 to 110 Fahr., with a weaker current ; No. 3 is to be worked at 70 Fahr. ; and No. 4 may be used cold. It is stated that solutions i and 4 yield thick deposits without requiring alternate deposition and scratch-brushing. Since during the working less tin is dissolved from the anodes than is deposited, the oxide or other salt of the metal must be added from time to time, except in the case of No. 3, which acts upon the anode more freely than the others. In tinning cast iron in these solutions, they require first to have a deposit of copper put upon them. For tinning zinc articles, No. I solution is employed. Steele's Process. This process is applied to coating articles of copper, brass, steel, iron, and zinc with tin. The solution is prepared thus : Dissolve 60 pounds of common soda, 15 pounds of pearlash, 5 pounds of caustic potash, and 2 ounces of cyanide of potassium in 75 gallons of water, then filter the solution ; next add 2 ounces of acetate of zinc, 16 pounds of peroxide of tin, and stir the mixture until all is dissolved, when the solution is ready for use. The solution is to be worked at about 75 Fahr. In preparing articles for electro -tinning, they must be rendered per- fectly clean, either by scouring or dipping. Articles of cast iron may advantageously be first coppered in an alkaline coppering bath. Some- 338 DEPOSITION AND ELECTRO-DEPOSITION OF TIN. times a deposit of tin is given in a boiling-hot solution by the zinc- contact method, and a stouter deposit afterwards obtained by the separate current in either of the foregoing solutions. The process of electro-tinning has been much adopted in France, and during the past few years there has been considerable attention paid to it in this country. It has yet to be developed into a really extensive industry. Electro-Tinning Sheet-Iron. Spence's Process. This inventor says . When it is desired to make tin plates as cheaply as possible, I first place the plates in a solution of zinc, and deposit that metal on the surface ; and then put them in a solution of tin, and deposit a coating of that metal. In manufacturing these plates, I coat the sheet iron with zinc, as before, and then deposit a coating of lead by electricity." By this method he reduces the quantity of tin usually required ; and in regard to terne plates, he dispenses with the use of tin altogether. When removed from the bath, the electro -tinned plates are brightened by being placed in a stove heated to a tempera- ture slightly above that at which tin melts (442 Fahr.). As the plates are taken out of the tinning bath, they are placed in a rack capable of containing 24 pieces. These racks, as they are filled, are placed in the stove, where they are allowed to remain until the tin melts on the surface. The plates are afterwards passed through rollers, with that edge first which was at the bottom of the rack. To avoid the employment of heat, one or more pairs of polished steel rollers may be used in suc- cession, and so adjusted as to bear on the plate with some pressure. On removing the plates from the bath, they are passed through the rollers, which remove inequalities of the tin surface. To give the necessary polish, the plates are then placed on a table, on which is a pair of rolls rotating at high speed, and coated with cloth or other suitable material. These rolls are so arranged " as to rotate in the reverse direction to the transverse of the plate, and hence the plate has to be pushed through them." Recovery of Tin from Tin Scrap by Electrolysis. Dr. J. H. Smith, in a paper read before the Society of Chemical Industry, described a method for working up tin scrap which he found to be successful. The scrap to be dealt with had, on an average, about 5 per cent, of tin and there was a supply of some 6 tons a week, for which quantity the plant was arranged. It was designed to convert the tin into chloride of tin for dyers' use, the iron scrap being utilised as copperas. On the recommendation of Messrs. Siemens and Halske, of Berlin, one of their dynamos (C. 18), was used. The machine in question was stated to give a current of 240 amperes, with an electro- motive force of 15 volts, and an expenditure of 7 -horse power. Eight baths were used, made of wood lined with rubber. They were EECOVERY OF TIN FROM TIN SCRAP BY ELECTROLYSIS. 339 i^ metres long, 70 centimetres wide, and i metre deep. The anodes were, of course, formed of the tin scrap, which was packed in baskets made of wood, and of a size to hold 60 kilos to 70 kilos of the scrap. There was an arrangement for constantly agitating these baskets by raising and lowering them, thus promoting circulation of the solution and regularity of action. The cathodes were copper plates i% milli- metres thick and 120 centimetres long by 95 centimetres broad. There were sixteen of these, placed two in each tank, one on each side of the basket. The electrolyte used was sulphuric acid, diluted with 9 volumes of water. The tin precipitated was rather over 2 kilos per hour ; it was very pure, easily melted when required, and in a form very suitable for solution in acid for preparation of tin salts. Dr. Smith having worked his process in a district in Grermany, where pro- bably tin scrap was obtainable at a low price, was enabled to show that a profit could be obtained upon the working. The same results might possibly be obtained in Birmingham, London, and other dis- tricts where large quantities of sheet tin are used. There have been many patents taken out for the electrolytic treatment of tin scrap, but the expense of collecting the scrap has always been the chief difficulty in rendering such processes commercially available. CHAPTER XXV. ELECTRO -DEPOSITION OF IRON AND ZINC. Electro-deposition of Iron ; Facing Engraved Copper-plates. Klein's Pro- cess for Depositing Iron upon Copper. Jacob! and Klein's Process. Ammonio-sulphate of Iron Solution. Boettger's Ferrocyanide Solution. Ammonio-chloride of Iron Solution. Sulphate of Iron and Chloride of Ammonium Solution. Electro-deposition of Zinc. Zincing Solu- tions. Person and Sire's Solution. Deposition of Zinc by Simple Im- mersion. Hermann's Zinc Process. Electro-deposition of Iron. Facing Engraved Copper -plates. The extreme hardness of electro -deposited iron as compared with, copper and type metal has caused the electro -deposition of iron to be applied to the facing of printers' type and engraved copper-plates, by which their durability is greatly augmented. The importance of protecting the surface of engraved copper-plates from the necessary wear and tear of the printing operations can scarcely be over- estimated, and a deposit of iron answers this purpose admirably. Another great advantage of the iron or " steel facing," or, as it is termed in France, acierage, is that when the deposited metal begins to wear off, the old coating is readily removed from the surface by means of dilute sulphuric acid, and another deposit given in its place in a very short time. In this way copper -plates may be preserved almost for an indefinite period, while each impression from the plate is as sharp and distinct as another even after a vast number of copies have been printed from the same plate. This system of facing printers' type and engraved copper -plates which was originally sug- gested by Boettger and the plates used for printing bank notes, has been much adopted by several large firms, including the eminent firm by whom this work was printed. Iron may readily be deposited from a solution of its most common salt, the protosulphate, or green copperas, but for this purpose the salt should be as pure as possible. A depositing solution may also be prepared by passing a strong current through a large iron anode suspended in a tolerably strong solution of sal ammoniac. After the electrolytic action has been kept up for an hour or so, a cathode of KLEIN'S PROCESS FOR DEPOSITING IRON UPON COPPER. 341 clean sheet brass or copper should be substituted, which, if the solu- tion has become sufficiently impregnated with metal, will at once receive a coating of iron, of a good white colour, though not perhaps quite so bright as the deposit obtained from a solution of the proto- sulphate of iron. An iron -depositing solution may be made in the same way by employing a moderately strong solution of either acetate of ammonium or acetate of potassium. A mixture of two parts sulphate of iron and one of sal ammonaic dissolved in water may also be employed, but the solution should not be too strong, otherwise the deposit is apt to be irregular, and of an indifferent colour. In making up iron baths for the electro-deposition of this metal, it has commonly been the practice to employ somewhat concentrated solutions, but the author, in the course of a long series of experiments, found that in most cases such a condition was far from being necessary and that weaker baths frequently yielded better results. The author has obtained deposits of iron from most of its salts, including those prepared with the vegetable acids, as the acetate, citrate, tartrate of iron, &c., from some of which exceedingly interest- ing results were obtained, but possessing, however, no practical signi- ficance. The results of some of the more useful experiments are given in the Appendix. Klein's Process for depositing Iron upon Copper. This process, which from its successful results obtained the recognition and support of the Russian Government, is specially applicable to the production of electrotypes, as a substitute for those produced from copper, and is stated to be eminently successful in bank-note printing. The solution is prepared in a very simple way, as follows : A solution of sulphate of iron is first made, and to this is added a solution of carbonate of ammonia until all the iron is thrown down. The precipitate is then to be washed several times, and afterwards dissolved by sulphuric acid, care being taken not to use an excess of acid. The solution is to be used in as concentrated a state as possible. To prevent the iron bath from becoming acid by working, a very large iron anode is employed about eight times larger in surface than that of the copper cathode to be coated. After working this bath for some time, M. Klein found that the deposition became defective, and this he dis- covered was due to the presence of acid in the bath, owing to the anode not having supplied the solution with its proper equivalent of iron to replace that which had been deposited. To overcome this, he attached a copper or platinum plate to the anode, by which the two plates formed a separate voltaic pair in the liquid, causing the iron (the positive metal) to become dissolved, while the battery current was not passing through the bath. It is stated that the iron deposited by this process is as hard as tempered steel, but very brittle ; it may, 342 ELECTRO- DEPOSITION OF IRON AND ZINC. however, be rendered malleable by annealing, when it may be engraved upon as easily as soft steel. The following process is given for copy- ing engraved metal plates in electrotype, and then giving them a surface of iron. To Copy Engraved Metal Plates and Face them with Iron. "If tha plate be of steel, boil it one hour in caustic potash solution. Brush and wash it well. "Wipe it dry with a rag, and then with one moistened with benzine. Melt six pounds of the best gutta-percha very slowly indeed, the gum being previously cut up into very small pieces. Add to it three pounds of refined lard, and thoroughly incor- porate the mixture. Pour the melted substance upon the centre of the plate. Allow it to stand twelve hours, and then take the copy off. " Phosphoric Sohition. Dissolve a fragment of phosphorus half -an - inck in diameter in one teaspoonful of bisulphide of carbon, add a similar measure of pure benzine, three drops of sulphuric ether, and half-a-pint of spirit of wine. Wash the mould twice with this solu- tion, allowing it to dry each time. " Silver Sohition. Dissolve one -sixth of an ounce of nitrate of silver, in a mixture of half-a-pint of strong alcohol and half a teaspoonful of acetic acid ; wash the mould once with this liquid, and allow it to dry. " Copper Solution. Dissolve fifty-six pounds of sulphate of copper in nineteen gallons of water, and add one gallon of oil of vitriol. De- posit a plate of copper upon the mould in this solution. "Iron Solution. To coat the copper plate with a surface of iron, dissolve fifty-six pounds of carbonate of ammonium in thirty-five gallons of water. Dissolve iron into the liquid, by means of a clean anode of charcoal iron and a current from a battery. Clean the anode frequently, and add one -pound of carbonate of ammonium once a week. The copper plate, before receiving the deposit, should be cleansed with pure benzine, then with caustic potash, and thoroughly with water. Immerse the cathode in the iron solution for four minutes, take it out, wash, scrub, replace in the vat, remove and brush it every five minutes, until there is a sufficient deposit ; then wash it thoroughly, well dry, oil, and rub it, and clean with benzine' If it is not to be used at once, coat it with a film of wax." Jacob! and Klein's Process. For depositing iron upon moulds for reproducing engraved surfaces and for other useful purposes, the fol- lowing process is given. A bath is prepared with a solution of sul- phate of iron, with the addition of either sulphate of ammonia, potash, or soda, which form double salts with the salt of iron. The bath must be kept as neutral as possible, though a small quantity of a weak organic acid may be added to prevent the precipitation oi salts of peroxide of iron. A small quantity of gelatine improves the JACOBI AND KLEIN'S PEOCESS. 343 texture of the deposit. To accelerate the rapidity of the deposit, and favour its uniform deposition, the solution should be warm. The anodes employed are large iron plates, or bundles of iron wire, and since it is found that the anodes do not dissolve with sufficient rapidity to keep up the normal metallic strength of the bath, the inventors have found it useful to employ anodes of gas carbon, copper, or platinum or any metal which is electro -negative to iron as well as the iron anodes ; or these auxiliary anodes may be placed in separate porous cells, excited by dilute sulphuric or nitric acid, or the nitrates or sulphates of potash or soda. The current employed is either from one or two Daniell cells only, or from a single Smee, the size of which is propor- tionate to the surface of the cathode. The Daniell cells should have a large surface, and the zinc be excited by a solution of sulphate of magnesia instead of dilute sulphuric acid. It is said to be " indispen- sable that the current should be regulated and kept always uniform with the assistance of a galvanometer having but few coils, and there- fore offering only a small resistance. The intensity of the current ought to be such as to admit only of a slight evolution of gas bubbles at the cathode ; but it would be prejudicial to the beauty of the deposit if gas bubbles were allowed to adhere to its surface." In working this process, the same moulds used for electrotyping may be employed ; but it is advisable in using lead or gutta-percha moulds to first coat them with a film of copper in the usual way, and after rinsing to place them at once in the iron solution. The film of copper may be afterwards removed, either by mechanical means or by dipping in strong nitric acid. The following formula is given for the composition of the iron bath : Sulphate of iron 139 parts. magnesia . . . . 123 These substances are to be dissolved together in hot water, with the addition of a little oxalic acid and some iron shavings. This solution should be kept, in its concentrated condition, in well- stoppered glass bottles or carboys, and when required for use must be diluted until it has a specific gravity of 1*155 (water being I'ooo). When working this solution, the oxide of iron, which appears at the surface of the liquor must be skimmed off, with some of the solution, and shaken up in a bottle with a little carbonate of magnesia, and after settling, the clear liquor may be returned to the bath. To prevent air-bubbles from adhering to the mould, while in the bath, the mould may be first washed with alcohol, and afterwards with water ; it is then to be placed in the bath before it has time to become dry. It is said that the iron deposited by this process is very hard and brittle, therefore 344 ELECTRO-DEPOSITION OF IRON AND ZINC. much care must be taken to avoid breaking the electro -deposit when separating it from the mould. When annealed, however, the iron acquires the malleability and softness of tempered steel, and has a remarkably fine appearance when brushed with carbonate of mag- nesia. Amongst the numerous solutions recommended for the electro - deposition of iron, we select the following : Ammonio-sulpjiate of Iron Solution. This double salt, which was first proposed by Boettger for depositing this metal, may be readily prepared by evaporating and crystallising mixed solutions of equal parts of sulphate of iron and sulphate of ammonia ; a solution of the double salt yields a fine white deposit of iron with a moderate current, and has been very extensively employed in "facing " engraved copper- plates. When carefully worked, this is one of the best solutions for the deposition of iron upon copper surfaces. Boettger 's Ferrocyanide Solution. This solution, which is con- sidered even better than the former for coating engraved copper-plates with iron, is formed by dissolving 10 grammes of ferrocyanide of potas- sium (yellow prussiate of potash) and 20 grammes of Rochelle salt in 200 cubic centimetres of distilled water. To this solution is added a solution consisting of 3 grammes of persulphate of iron in 50 cubic centimetres of water. A solution of caustic soda is next added, drop by drop, with constant stirring, to the whole solution, until a per- fectly clear light yellowish liquid is obtained, which is then ready for immediate use. Mr. Walenn obtained good results from a slightly acid solution of sulphate of iron (i part to 5 of water). Sulphate of ammonia, how- ever, was found to increase the conductivity of the solution. Ammonio- chloride of Iron Solution, made by adding sal-ammo- niac to a solution of protochloride of iron, may also be used for de- positing iron, a moderately strong current being employed. When carefully prepared and worked, this solution is capable of yielding very good results, but it has these disadvantages : the solution becomes turbid, and a shiny deposit is apt to form upon the electrodes. It is a common defect in iron solutions that they are liable to undergo change by absorbing oxygen from the air. To overcome this, Klein adopted the ingenious expedient of adding glycerine to the solution, by which he was enabled to keep his solution bath tolerably clear, except on the surface, upon which a shiny foam accumulated, which became deposited upon the articles in solution. To prevent the air from injuriously affecting the baths, it is advisable that the depositing vessel should be kept covered as far as practicable. Sulphate of Iron and Chloride of Ammonium Solution. The addition of chloride of ammonium (sal-ammoniac) to sulphate of iron ELECTRO-DEPOSITION OF ZINC. WATT'S SOLUTION. 345 solution improves the character of the deposit while improving the conductivity of the solution. Meidinger found that engraved copper- plates coated with iron in a bath thus composed were capable of yielding from 5,000 to 15,000 impressions. Electro-deposition of Zinc. Watt's Solution. The deposition of this metal has never attained the dignity of a really practical art. In the earlier periods of electro -deposition many iron articles, including the sheet metal, were coated with zinc by this means, to protect them from rust, or oxidation, but it was soon found that the porous and granular nature of the coating, instead of acting as a preservative from rust, greatly accelerated the action of moisture upon the underlying metal (iron) by promoting electro -chemical action, by which the iron really suffered more severely than would ordinary sheet iron from which the scale, or coating of black oxide of iron, had not been removed. The process of galvanising iron, as it is fancifully termed by which articles of this metal are dipped into a bath of molten zinc soon proved, although not altogether faultless, so vastly superior to that of electro - zincing, that it became generally adopted to the entire exclusion of the latter. There are many purposes gauze wire, for example to which the process of "galvanising" is inapplicable, and for which a good electro -deposit of zinc would be specially serviceable. To obtain a solution which would give a good reguline deposit of zinc suitable for such purposes, the author, after a long series of experiments, succeeded in forming a solution, for which he obtained a patent in 1855, from which he obtained some exceedingly beautiful de- posits, possessing the fullest degree of toughness which this metal exhibits when in a perfectly pure state. The most satisfactory result was obtained by dissolving the best milled zinc in a strong solution of cyanide of potassium, with the addition of liquid ammonia, by means of a strong voltaic current. The process is briefly as fol- lows : 200 ounces of cyanide of potassium are dissolved in 20 gallons of water ; to this solution is added 80 ounces, by measure, of strong liquid ammonia. The whole are then well stirred together. Several large porous cells are then filled with the solution, and these are placed upright in the vessel containing the bulk of the solution, the liquids in each vessel being at an equal height. Strips of copper are then connected by wires to the negative pole of a compound Bunsen battery of two or more cells, and these strips are immersed in the porous cells. A large anode of good milled zinc, previously well cleaned, is now connected to the positive pole of the battery, and the plate suspended in the larger vessel. The voltaic action is to be kept up until the zinc has become dissolved to the extent of about 60 ounces, or 3 ounces to each gallon of solution. To this solution is added 80 ounces of carbonate of potash, by dissolving it in portions of 346 ELECTRO-DEPOSITION OF IRON AND ZINC. the solution at a time, and returning the dissolved salt to the bath. The porous cells being removed, the solution is allowed to rest for about twelve hours, when the clear liquor is to be transferred to another vessel, the last portions, containing sedimentary matter, being filtered into the bath. Preparing Cast and Wrought Iron Work for Zincing. The articles require to be first dipped for a short time in a hot potash bath, after which they are to be well rinsed. They are next steeped in a ' ' pickle ' ' composed of oil of vitriol half-a-pound, water I gallon. As soon as the black coating of oxide yields to the touch the articles are removed and plunged into clean cold water ; they are then taken out one by one and well brushed over (using a hard brush) with sand and water ; if any oxide still remains upon the surface, the articles must be immersed in the pickle again, and allowed to remain therein until, when the brushing is again applied, they \eadily become cleaned. They are now to be well rinsed, and at once suspended in the zincing bath, in which they should remain for a few minutes, then taken out and ex- amined ; and if any parts refuse to receive the deposit, these must be again well sand-brushed or scoured, the article being finally brushed all over, again rinsed, and placed in the depositing bath, where they are allowed to remain until sufficiently coated. An energetic current from at least two 3 -gallon Bunsen cells, where a dynamo -machine is not used, is necessary to obtain a good deposit. The articles may be rendered bright by means of the scratch-brush, but large articles may be sufficiently brightened by means of sand and water, with the assistance of soap. When finished they should be dipped into hot water, and may then be further dried by means of hot sawdust. The anodes should be of the best milled zinc, and well cleaned before using. Zincing Solutions. For the electro -deposition of zinc, solutions of the sulphate, ammonio- sulphate, chloride, and ammonio- chloride may be employed, as also alkaline solutions prepared by dissolving zinc oxide or carbonate in a solution of cyanide of potassium or caustic potassa ; the deposit from either of these alkaline solutions is generally of very good quality, and if too strong a current be not employed, the deposited metal is usually very tough. Person and Sire's Solution. This consists of a mixture of 1 part of oxide of zinc dissolved in 100 parts of water, in which 10 parts of alum have been previously dissolved at the ordinary temperature. The current from a single battery cell is employed, and the anode surface should be about equal to that of the articles to be coated, when, it is stated, the deposition proceeds as easily as that of copper, and takes place with equal readiness upon any metal. Deposition of Zinc by Simple Immersion. According to DEPOSITION OF ZINC BY SIMPLE IMMERSION. 347 Roque, cast and wrought-iron articles may be coated with zinc in the following way : A mixture is first made consisting of (by measure) hydrochloric acid 550 parts, sulphuric acid 50 parts, water 1,000 parts, and glycerine 20 parts. The iron articles are first pickled in this mixture and then placed in a solution composed of carbonate of potassa 1 part and water 10 parts. The articles are next to be immersed from three to twelve hours in a mixture composed as follows: water 1,000, chloride of aluminium 10, bitartrate of potassium 8, chloride of tin 5, chloride of zinc 4, and acid sulphate of aluminium 4 parts. The thickness of the deposit is regulated by the length of the immersion. Hermann's Zinc Process. By this process, which was patented in Grermany in 1883, zinc is deposited by electrolysis from dilute solu- tions of sulphate of zinc with the aid of sulphates of the alkalies, or alkaline earths potassium, sodium, ammonium, strontium magne- sium, or aluminium either added singly, or mixed together. The addition of these salts is only advantageous when dilute solutions of sulphate of zinc are to be treated. According to Kiliani, during the electrolysis of a solution of sulphate of zinc of 1-33 specific gravity (the anodes and cathodes consisting of zinc plates), the evolution of gas is greatest with a weak current, diminishing with an increasing current, and ceasing when on one square centimetre electrode surface, three milligrammes of zinc are precipitated per minute. The deposit obtained with a strong current was very firm. From a 10 per cent, solution the deposit was best with a current yielding from 0-4 to 0-2 milligramme of zinc. From very dilute Solutions the zinc was always obtained in a spongy condition, accompanied by copious evolutions of hydrogen. With a weak current and from a I per cent, solution, oxide of zinc was also precipitated, even with an electro -motive force of 17 volts, when only 0^0755 milligramme of zinc per minute was deposited on one square centimetre of cathode surface. The size of the electrode surfaces must therefore be adjusted according to the strength of the current and the degree of concentration of the elec- trolyte. CHAPTER XXVI. ELECTRO-DEPOSITION OF VARIOUS METALS. Electro-deposition of Platinum. Electro-deposition of Cobalt. Electro- deposition of Palladium. Deposition of Bismuth. - Deposition of Antimony. Deposition of Lead. Metallo-Chromes. Deposition of Aluminium. Deposition of Cadmium. Deposition of Chromium. Deposition of Manganium. Deposition of Magnesium. Deposition of Silicon. THEEE are many metals which have been deposited by electrolysis more as a matter of fact than as presenting any practical advantage in a commercial sense ; others, again, possessing special advantages which would render their successful deposition a matter of some importance, have been the subject of much experiment, in the hope that the difficulties which stood in the way of their being practically deposited for useful purposes could be overcome. Of these latter, the intractable but most valuable metal, platinum, may be considered the most important. Electro-deposition of Platinum. The peculiar attributes of this interesting metal its resistance to the action of corrosive acids, and of most other substances, render it invaluable in the construction of chemical apparatus, while its high cost, its infusibility, and the great difficulty experienced in giving this metal any required form, greatly limit the area of its usefulness. If, however, articles of copper, brass, or German silver metals which may be so readily put into shape by casting, stamping, or by any ordinary mechanical means could be successfully and economically coated with platinum, this branch of the art of electro -deposition would soon meet with considerable sup- port from the manufacturers of chemical apparatus, as also from opticians, who would gladly adopt electro -platinised* articles for many purposes of their art. * To contradistinguish the art of depositing bright reguline platinum upon metals from the process of platinising, devised by Smee for imparting a black powdery film upon silver for the negative plates of voltaic batteries, the term platinating has been proposed, but we would suggest that a simpler term would be platining. Electro-platinising would be a more correct term than platinating. ELECTRO -DE POSITION OF PLATINUM. 349 One great difficulty that stands in the way of depositing platinum economically and of any required thickness is that the anodes do not dissolve in the solutions which have as yet been adopted for its depo- sition ; consequently, unless repeated additions of a platinum salt are made as the solution becomes exhausted, it is impossible to obtain a coating of sufficient thickness for any practical purpose. In order to meet this difficulty in some degree, the author suggested in his former work that the strength of the solution may be kept up in the same way as he recom- mended for electro -tinning; that is to say, a reservoir, containing concentrated platinum solution, is placed upon a shelf a little above the electro -platinising bath (Fig. 1 1 8), and the strong liquid is allowed to drip or flow out through a tap in the reser- voir, and trickles at any required speed, into the solution bath, while deposition is going on, and in this way the strength of the bath may be kept up to any desired density. For small quanti- ties of solution, the funnel arrangement shown in Fig. 119 may be adopted. The concentrated platinum solution being made in part from a portion of the larger solution, instead of with water, the original quantity of the liquid may be very fairly balanced. For example, if we take, say, one quart of the platinising solution and add to this a considerable proportion of platinum salt and the solvent employed in its preparation, so as to make as strong a solution as possible, when this is added and returned to the bath in the way above indicated, it will not add much to its original bulk. By weighing the articles before and after immersion, the weight of metal deposited may soon be ascertained (the time occupied being noted), and if the exact percentage of metal in the concentrated liquor is previously determined, there will be no difficulty in determining at what speed the strong solution should be allowed to flow into the bath to keep it up to the proper strength. Another suggestion we have to make is this : since the platinum anode does not become dissolved during electrolysis, a carbon anode maybe substituted, which, in large opera- tions, would add much to the economy of the process. Preparation of Chloride of Platinum. As in the case of gold, this metal must first be dissolved in aqua regia, to form chloride of platinum, previous to making up either of the baths about to be described. For this purpose, fragments of platinum, which may be pieces of foil or wire, are put into a glass flask, and upon them is to be poured two to three parts of hydrochloric acid and one part nitric acid ; the flask is then placed on a sand bath, and gently heated until the red fumes at 35 ELECTRO-DEPOSITION OF VARIOUS METALS. first given off cease to appear in the bulb of the flask. A solution of a deep red colour is formed, which must now be carefully poured into a porcelain evaporating dish, placed on the sand bath, and heated until nearly dry, moving the vessel about, as recommended in treating chloride of gold, until the thick blood-red liquor ceases to flow, at which period the vessel may be set aside to cool. Any undis- solved platinum remaining in the flask may be treated with nitro- hydrochloric acid as before until it is all dissolved. The dry mass is to be dissolved in distilled water, and the subsequent solution, after evaporation, added to it. If the original weight of the platinum is known, it is a good plan to dissolve the dried chloride in a definite quantity of distilled water, so that in using any measured portion of the solution, the percentage of actual metal used may be fairly deter- mined when making up a solution. Cyanide of Platinum Solution. Take a measured quantity of the chloride of platinum solution representing about five pennyweights of metal, and add sufficient distilled water to make up one pint. Now add of strong solution of cyanide sufficient to precipitate and redis- solve the platinum ; add a little in excess, filter the solution, and make up to one quart with distilled water. The solution must be heated to about 130 Fahr. when using it. A rather weak current from a "Wollaston or Daniell battery should be used ; if too strong a current be applied, the deposit will probably assume the form of a black powder. Deposition by Simple Immersion. Platinum readily yields itself up when brass, copper, German silver, &c., are immersed in its solutions, but the deposit is of little or no practical use. It may also be depo- sited from its solution by contact with zinc as follows : Powdered carbonate of soda is added to a strong solution of chloride of platinum until no further effervescence occurs ; a little glucose (grape sugar) is then added, and lastly, as much common salt as will produce a whitish precipitate. The articles of brass or copper are put into a zinc colander and immersed in the solution, heated to about 140 Fahr., for a few seconds, then rinsed and dried in hot sawdust. Deposition by Battery Current. Roseleur describes a solution from which he obtained platinum deposits of considerable thickness. The solution is prepared as follows : Platinum, converted into chloride . . 10 parts. Distilled water . . 500 Dissolve the chloride in the water, and if any cloudiness appears in the solution, owing to the chloride having been over-heated during the last stage of the evaporation, it must be passed through a filter. ELECTRO-DEPOSITION OF PLATINUM. 35! Phosphate of ammonia (crystallised) . 100 parts. Distilled water 500 ., Dissolve the phosphate in the above quantity of water, and add the liquid to the platinum solution, with brisk stirring, when a copious precipitate will be formed. To this is next added a solution of phos- phate of soda, consisting of Phosphate of soda . , .. . 500 parts. Water (distilled) , ._ ..-_ , . . 1,000 The above mixture is to be boiled until the smell of ammonia ceases to be apparent, and the solution, at first alkaline, reddens blue litmus paper. The yellow solution now becomes colourless, and is ready for use. This solution, which is to be used hot, with a strong battery current, is recommended for depositing platinum upon copper, brass, and German silver, but is unsuited for coating zinc, lead, or tin, since these metals decompose the solution and become coated in it by simple immersion. Since the platinum anode is not dissolved in this solu- tion, fresh additions of the chloride must be made when the solution has been worked. Boettger's Solution for Depositing Platinum consists of a boiling-hot mixture of chloride of platinum solution and chloride of ammonia (sal-ammoniac), to which a few drops of liquid ammonia are added. The solution, which is weak in metal, requires to be revived from time to time by additions of the platinum salt. Electro-deposition of Cobalt. Until somewhat recently the elec- tro-deposition of cobalt had chiefly been of an experimental character, based upon the belief, however, that this metal, if deposited under favourable conditions, was susceptible of some useful applications in the arts. The difficulty of obtaining pure cobalt anodes as was the case with nickel until a comparatively few years ago as a commer- cial article, stood in the way of those practical experimentalists who would be most likely to turn the electro -deposition of this metal to account. Moreover, the extremely high price of the metal, even if rudely cast in the form of an ingot, rendered its practical application all but impossible. That unfavourable epoch is now passed, and we have cobalt anodes and " salts " in the market, as easily procurable, though not, of course, at so low a price, as the corresponding nickel products. The author is indebted to the courtesy of the enterprising firm of cobalt and nickel refiners, Messrs. Henry Wiggin & Co., of Birmingham, for some excellent examples of their single and double cobalt salts and rolled cobalt anodes, and is thus enabled to state that those who may desire to embark in the electro -deposition of this metal can readily obtain the chief requisites, the salts and anodes, in 3$2 ELECTRO-DEPOSITION OP VARIOUS METALS. any desired quantity from this firm at the following rates : Rolled and cast cobalt anodes, 163. per lb.; single cobalt salts, 53. 6d. per Ib. ; double cobalt salts, 43. 6d. per lb. Characteristics of Cobalt. Believing that this metal is destined to take an important position in the art of electro -deposition at no dis- tant period, a few remarks upon its history, and the advantages which it presents as a coating for other metals, may not be unwelcome. Cobalt, like its mineral associate, nickel,* was regarded by the old German copper miners with a feeling somewhat akin to horror, since its ore, not being understood, frequently led them astray when search- ing for copper. Brande says, " The word cobalt seems to be derived from Cobalus, which was the name of a spirit that, according to the superstitious notions of the times, haunted mines, destroyed the labours of the miners, and often gave them a great deal of unneces- sary trouble. The miners probably gave this name to the mineral out of joke, because it thwarted them as much as the supposed spirit, by exciting false hopes, and rendering their labour often fruitless ; for as it was not known at first to what use the mineral could be applied, it was thrown aside as useless. It was once customary in Germany to introduce into the church service a prayer that God would preserve miners and their works from kobalts and spirits. Mathesius, in his tenth sermon, where he speaks of cadmia fossilis (probably cobalt ore) says, ' Ye miners call it cobalt : the Germans call it the black devil, and the old devil's hags, old and black kobel, which by their witchcraft do injury to people and to their cattle.' " In chemical works cobalt is generally described as a reddish-grey metal, and this fairly represents the tone of its colour, though a warm steel grey would perhaps be a more appropriate term. When depo- sited by electrolysis under favourable conditions, however, cobalt is somewhat whiter than nickel, but it acquires a warmer tone after being exposed to the air for some time. Becquerel states that cobalt, deposited from a solution of its chloride, " has a brilliant white colour, rather like that of iron; " while Gaiffe says that, when deposited from a solution of the double sulphate of cobalt and ammonium, it is " superior to nickel, both in hardness, tenacity, and beauty of colour." Wahl remarks, " The electro -deposits of this metal which we have seen equal, if indeed they do not surpass, those of nickel in whiteness and brilliancy of lustre." Much of the beauty of electro -deposited cobalt depends, not only upon the electrolyte employed, but also upon the quality of the current, as is also the case with nickel, and indeed most other metals and their alloys. * Nickel was called, by the old German miners, kupfernickel, or " falae copper." DEPOSITION OF COBALT. 353 According to Deville, cobalt is one of the most ductile and tenacious of metals, its tenacity being almost double that of iron. It is fused with great difficulty, but more readily when combined with a little carbon, in which respect, as in many other characteristics, it bears a close resemblance to its mineralcgical associate, nickel. It is soluble in sulphuric and hydrochloric acids, but more freely in nitric acid. Cobalt Solutions. The salts most suitable for making up cobalt baths are: I. Chloride of cobalt, rendered neutral by ammonia or potash ; 2. the double chloride of cobalt and ammonium ; and 3, tha double sulphate of cobalt and ammonium. Chloride of Cobalt. The single salt (chloride) may be prepared by dissolving metallic cobalt or its oxides (the latter being the most readily soluble) in hydrochloric acid, and evaporating the solution to dryness. The residuum is then heated to redness in a covered crucible, when a substance of a bright blue colour is obtained, which is pure chloride of cobalt. When this anhydrous (that is without water) chloride of cobalt is dissolved in water it forms a pink solution, which, by careful evaporation, will yield crystals of a beautiful red colour. This is hydrated chloride of cobalt, from which various cobalt baths may be prepared according to the directions given below. BecquereVs Solution. This is formed by neutralising a concentrated solution of the chloride of cobalt by the addition of ammonia or caustic potash, and adding water in the proportion of I gallon to 5 ounces of the salt. The bath is worked with a very weak current, and the deposit is in coherent nodules, or in uniform layers, according to the strength of the current. The deposited metal is brilliantly white, hard, and brittle, and may be obtained in cylinders, bars, and medals, by using proper moulds to receive it. The deposited rods are mag- netic,* and possess polarity. If an anode of cobalt be used, the solu- tion is of a permanent character. A portion of the chlorine is disen- gaged during the electro -deposition, and if iron be present in the solution, the greater portion of it is not deposited with the cobalt. Beardslee's Solution. The following has been recommended by Mr. G-. W. Beardslee, of Brooklyn, New York, and is stated to yield a good deposit of cobalt, which is "very white, exceedingly hard, and tenaciously adherent." Dissolve pure cobalt in boiling muriatic acid, and evaporate the solution thus obtained to dryness. Next dissolve from 4 to 6 ounces 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 alkaline, is ready for use. Battery power of from two to five Smee cells will be suffi- cient to do good work. Care must be taken not to allow the solution * Faraday says that perfectly pure cobalt is not magnetic. AA 354 ELECTRO-DEPOSITION OF VARIOUS METALS. to lose its slightly alkaline condition, upon which the whiteness, uniformity of deposit, and its adhesion to the work greatly depend. Boettger^s Solution. Boettger states that from the following solu- tion a brilliant deposit of metallic cobalt was obtained by means of a current from two Bunsen cells. Chloride of cobalt . ... 40 parts. Sal-ammoniac 20 Liquid ammonia ..... 20 Water 100 By another formula it is recommended to dissolve five ounces of dry chloride of cobalt in one gallon of distilled water, and make the solution slightly alkaline by means of liquid ammonia. A current from three to five Smee cells is employed, with an anode of cobalt. The solution must be kept slightly alkaline by the addition of liquid ammonia whenever it exhibits an acid reaction upon litmus paper. Since these solutions are liable to become acid in working, it is a good plan to keep a strip of litmus paper floating in the bath, so that any change of colour from blue to red may be noticed before the altered condition of the bath has time to impair the colour and character of the deposited metal; if some such precaution be not adopted, the deposit may assume a black colour and necessitate the rescouring of the work. Double Sulphate of Cobalt and Ammonia. Cobalt is freely deposited from a solution of the double salt, of a fine white colour, provided that an excess of ammonia be present in the bath. From four to six ounces of the double salt may be used for each gallon of water in making up a bath, according to the strength of current employed. The solution of this salt and that of the double chloride more readily yield up their metal than the corresponding salts of nickel, therefore a propor- tionately smaller quantity of the metallic salts are required to make up a cobalting bath. Electro-deposition of Palladium. This metal may be deposited more freely from its solution than platinum ; it is dissolved in aqua regia and treated in the same way as the latter metal, and the dry salt dissolved in distilled water. The palladium is then precipitated by means of a solution of cyanide of potassium, and the precipitate redis- solved by an excess of the same solution. Since a palladium anode becomes dissolved in the cyanide bath, deposits of any required thick- ness may be obtained. This metal may also be deposited from a solution of the ammonio- chloride, using a palladium anode, and a scurrent from two or three Smee cells. M. Bertrand advises a neutral olution of the double chloride of palladium and ammonium for the DEPOSITION OF ANTIMONY. 355 electro -deposition of this metal either with or without the use of a voltaic battery. The deposition of palladium is, however, more inter- esting as a fact than of any practical use. Deposition of Bismuth. This metal may be dissolved in dilute nitric acid (2 parts acid to I part water) with moderate heat, and the solution evaporated and allowed to crystallise. The resulting salt is known as acid nitrate of bismuth, which may be dissolved in a very small quantity of distilled water ; but if the solution, even when acid, be poured into a large quantity of water it becomes decomposed, and forms a white, somewhat crystalline precipitate, commonly called subnitrate of bismuth, basic nitrate, or pearl white. If strong nitric acid be poured upon powdered bismuth the chemical action is intensely violent, and sometimes attended by ignition. Chloride of bismuth is formed by dissolving the metal in 4 parts of hydrochloric acid and i part nitric, by measure. The excess acid is afterwards expelled by evaporation. To deposit bismuth upon articles of tin by simple immersion, Com- maille employs a solution formed by dissolving 10 grains of nitrate of bismuth in a wineglassful of distilled water, to which two drops of nitric acid have been added. After the article is immersed the bismuth will be deposited in very small shiny plates. The metal may also be deposited from this solution by means of the separate battery. The deposited metal is said to be explosive when struck by a hard sub- stance. Bismuth may be deposited from a cyanide solution, but since the anode is not freely acted upon by the cyanide the solution soon becomes exhausted. M. A. Bertrand states thai bismuth may be deposited upon copper or brass from a solution consisting of 30 grammes of the double chloride of bismuth and ammonium, dissolved in a litre of water, and slightly acidulated with hydrochloric acid. A current from a single Bunsen cell should be used. Deposition of Antimony. Chloride of antimony, terchloride of antimony, or, as the ancients termed it, butter of antimony, is thus pre- pared, according to the pharmacopoeias : I Ib. of prepared sulphuret of antimony is dissolved in commercial muriatic acid, 4 pints, by the aid of gentle heat, gradually increased to ebullition. The liquid is filtered until quite clear, then boiled down in another vessel to 2 pints ; it is then cooled, and preserved in a well -stoppered bottle. The solution has a specific gravity of i'49O. It is highly caustic. A solution of chloride of antimony may also be prepared by the electrolytic method, that is by passing a moderately strong current through an anode of antimony, immersed in hydrochloric acid, em- ploying a plate of carbon as the cathode, the action being kept up until a strip of clean brass, being substituted for the carbon plate, promptly receives a coating of antimony. 356 ELECTRO-DEPOSITION OF VARIOUS METALS. Another solution may be prepared by digesting recently precipi- tated teroxide of antimony in concentrated hydrochloric acid, and then adding an excess of free acid to the solution thus obtained. This solution yields a very quick and brilliant deposit of antimony upon brass or copper surfaces with a current from three small Daniell's cells, arranged in series, with electrodes of about equal surface. The fresh teroxide may be readily formed thus : Dissolve 4 ounces of finely powdered tersulphuret of antimony in I pint of muriatic acid, by the aid of gentle heat, by which a solution of terchloride of anti- mony is obtained ; filter the liquid, and then pour it into 5 pints of distilled water. By this dilution a greater part of the terchloride is decomposed, the chlorine unites with the hydrogen of the water, forming hydrochloric acid, and the oxygen of the water, being set free, unites with the antimony, forming a teroxide, that is, an oxide containing three equivalents of oxygen. The teroxide thus obtained is separated by filtration, and washed, to free it from acid. It is then washed with a weak solution of carbonate of soda, which decom- poses any terchloride present, leaving the teroxide free. It is then dried over a water bath, and preserved in a well-stoppered bottle. Antimony may also be deposited from a solution prepared by dis- solving oxychloride of antimony in strong hydrochloric acid, the latter being in excess. The oxychloride may be obtained by largely diluting with water a solution of the chloride of antimony, when a white precipitate falls, which is insoluble in water. The liquor is now to be poured off, and hydrochloric acid added until the precipitate is entirely dissolved. The resulting solution, which must not be diluted with water which decomposes it should be used with a moderate current and rather small anode surface, and the articles to be coated in it must be perfectly dry, and when the required deposit is obtained the article should be dipped in a strong solution of hydrochloric acid before being rinsed in water, otherwise a white insoluble film of oxy- chloride will form on the surface. A depositing bath may also be formed by mixing equal parts, by measure, of a solution of commercial chloride of antimony and sal- ammoniac. The solution thus formed is a very good conductor, deposits freely a good reguline metal, and is not so liable to yield deposits upon the baser metals by simple immersion as the former solution. A very good antimony bath may be made by dissolving tartar emetic (potassio-tartrate of antimony) in 2 parts hydrochloric acid and I part water, by measure; or, say, tartar emetic 8 Ibs., hydrochloric acid 4 Ibs., and water 2 Ibs., a larger proportion of water being added if desired. The resulting solution forms a very good bath for the deposition of antimony, and yields up its metal very freely. "With DEPOSITION OP LEAD. 357 the current from two to three Daniells the metal is deposited very quickly, and in a good reguline condition. To insure the adherence of the deposit, however, the anode surface should at first be small, until a film of moderate thickness has been obtained, after which it may be gradually increased until both electrodes are of about equal surface. The above solution is not affected by atmospheric influence nor by continual working, and would be very useful for small opera- tions for producing thick deposits of antimony ; but the cost of the mixture would preclude its adoption for any but purely experimental purposes. Deposition by Simple Immersion . The acid solution of chloride of antimony readily yields up its metal to brass by simple immersion, and by this means brass articles are coloured of a lilac tint. A solution is made for this purpose by adding a large quantity of water to a small quantity of chloride of antimony, when a dense white precipitate of oxychloride of antimony is formed. The mixture is boiled until this is nearly redissolved, when more water is added, and the boiling resumed. The liquor is then filtered, and the clear liquor heated to boiling ; into this the cleaned brass articles are placed, when they at once receive a coating of antimony of a lilac colour, being kept in the boiling solution until the desired shade of colour is obtained. After rinsing in clean water, the articles are dried in hot sawdust, then brushed clean and lacquered. Commercial chloride of antimony (butter of antimony) is also used for bronzing or browning gun -barrels, and when used for this purpose it is known as bronzing salt. To apply it for bronzing gun-barrels the chloride is mixed with olive-oil, and rubbed upon the barrel, slightly heated ; this is afterwards exposed to the air until the requisite tone is obtained ; a little aquafortis is rubbed on after the antimony to hasten the operation. The browned barrel is then carefully cleaned, washed with water, dried, and finally burnished or lacquered. When a piece of clean zinc is immersed in a solution of chloride of anti- mony the metal becomes reduced to a fine grey powder, which is em- ployed to give the appearance of grey cast-iron to plaster of Paris casts. Deposition of Lead. This metal is readily reduced from a solution of its nitrate or acetate as exemplified in the production of the well- known lead-tree; it may also be deposited upon zinc or tin from a solution formed by dissolving litharge (oxide of lead) in a solution of caustic potash. Iron articles will become coated, by simple immersion, in a solution of sugar of lead (acetate of lead). Becquerel * deposited lead upon a bright, cleaned surface of copper, in contact with a piece of zinc, in a solution of chloride of lead and sodium. This metal may * " The Chemist," vol. v. p. 408. 358 ELECTRO-DEPOSITION OP VARIOUS METALS. also be deposited, by means of the battery, from dilute solutions of acetate or nitrate of lead, or from a solution formed by saturating a boiling solution of caustic potash with litharge, employing a lead anode. The deposition of this metal is not, however, of any commercial im- portance. The electrolysis of salts of lead under certain conditions are, however, exceedingly interesting in what is termed metaUo- chromy, as will be seen below. Metallo-Cliromes. A remarkably beautiful effect of electro -chemi- cal decomposition is produced under the following conditions : A con- centrated solution of acetate of lead (sugar of lead) is first made, and after being filtered is poured into a shallow porcelain dish. A plate of polished steel is now immersed in the solution, and allowed to rest on the bottom of the dish (see Fig. 120). A small disc of sheet copper Fig. 1 20. is then to be connected to the wire proceeding from the zinc element of a constant battery of two or three cells, and the wire connected to the copper element is to be placed in contact with the steel plate. If now the copper disc be brought as close to the steel plate as possible, with- out 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 polished metallic surface beneath. By reflected light, every prismatic colour is visible, and by transmitted light a series of prismatic colours complementary to the first series will appear, occupying the place of the former series. The colours are seen to the greatest perfection by placing the plate before a window with its 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 consider- able amount of friction without being removed. In proof of the lead METALLO-CHROTWES. 359 oxide being deposited in films or layers, 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-coloured film will be laid bare, by the removal of the delicate film above it. The discovery of this interesting electrolytic phenomenon is due to Nobili, who in the year 1826 discovered that when a solution of acetate of lead was electrolysed by means of a current from four to six Grove cells, a large platinum anode and a platinum wire cathode being employed, prismatic colours were produced upon the anode surface ; and when the platinum anode was placed horizontally in the acetate solution and the negative wire held vertically above it, a series of rings in chromatic order were produced. These effects subsequently took the name of " Nobili 's rings," and the interesting discovery induced Becquerel, Gassiot, and others to experiment in the same direction by varying the strength of the current and employing other solutions than the acetate of lead. BecquereVs Solution. The following formula was suggested by Becquerel : * Dissolve 200 grammes of caustic potash in 2 quarts of distilled water, add 150 grammes of litharge, boil the mixture, for half an hour, and allow to settle. Then pour off the clear liquor, and dilute it with its own bulk of water. The plan recommended by Mr. Gassiot to obtain the tnetallo-chromes is to place over the steel plate a piece of card, cut into some regular device, as shown in the illustration, and over tihis a rim of wood, the copper disc being placed above this. "We have found that very beau- tiful 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 to the positive electrode as before ; indeed, this is one of the simplest and readiest methods of obtaining the colorations upon the polished metal. A few examples of metallb- chromes obtained in this way are shown in the frontispiece of this work. Metallo-chromy, as it is termed, is extensively employed in Nuremberg to ornament metallic toys, the solution used being that suggested by Becquerel, namely, a solution of the oxide of lead in caustic soda or potash. Metallo- chromy has also been adopted in France for colouring bells, and in Switzerland for colouring the hands and dials of watches. In using the lead solutions to produce metallo- chromes it must be remembered that metallic 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. * " The Chemist," vol. iv. p. 457. 360 ELECTRO-DEPOSITION OP VARIOUS METALS. Jkfetallo-chrotnes on Nickel-plated Surfaces. It will be obvious that if metallo-chromy were only applicable to platinum or steel surfaces which has generally been the case heretofore that the usefulness of the process as a means of ornamentation for industrial purposes would be greatly restricted. While the production of these colorations upon platinum foil would only be effected for experimental purposes, the application of the process to steel surfaces would necessarily be of a limited character, owing to the unsuitableness of this metal as com- pared with brass, German silver, and copper, for the manufacture of many articles of utility or ornament. With a view to extend the usefulness of these very beautiful colorations, and thus, to a certain extent, open up a new field for their application, the author some time since turned his attention to polished nickel-plated surfaces, as being, of all others, the most suitable, from their extreme brilliancy, to exhibit the rainbow tints of metallo-chromy. His first experiments were upon highly-polished surfaces of nickel-plated brass, and the results obtained were exceedingly satisfactory. The experiments were subsequently pursued under varied conditions of working, until the most satisfactory method of procedure was arrived at. A few of these results, obtained upon nickel-plated brass, are illustrated in the frontispiece to the present work; but the reader is referred to the Appendix for a detailed description of the method adopted to produce these colorations upon nickel -plated surfaces, and for some particulars as to salts of lead applicable to the purpose. Deposition of A*"*"" or Aluminium. This remarkable metal, which in an oxidised state (alumina) occurs most abundantly in nature as a constituent of all clays in combination with silica, was first obtained in the metallic state by Wohler in the following way : Chloride of aluminium and pure potassium are heated in a small platinum or porcelain crucible, the heat of a spirit-lamp being suffi- cient, for when the substances begin to react upon each other the temperature suddenly rises to redness. When the crucible is cold, its contents are well washed with cold water, by which a finely divided grey substance with a metallic lustre is obtained, which is pure aluminium. About the year 1854, Sainte-Claire Deville, of Paris, devoted his attention to this subject, substituting chloride of sodium for potassium, and heating the chloride of aluminium with this salt in a porcelain crucible to bright redness,* by which the excess of chloride of aluminium was disengaged, and in the middle of the resulting saline mass larger or smaller globules of perfectly pure aluminium were found. In reference to the characteristics of this metal, Deville says : * " The Chemist." Edited by John and Charles Watt. Vol. i., new series, 1854, DEPOSITION OF ALUMINIUM. 361 " It is completely unalterable, either in dry or humid air; it does not tarnish ; and remains brilliant where freshly-cut zinc or tin lose their polish. Sulphuretted hydrogen has no action upon it ; neither cold nor boiling water -will tarnish it ; nitric acid, whether weak or concentrated, or sulphuric acid employed cold, will take no effect upon it. Its real solvent is hydrochloric acid. ... It will be easily understood that a metal as white [?] and as unalterable as silver, which does not tarnish in the air, which is fusible, malleable, ductile, and yet tough, and which has the singular property of being lighter than glass, would be most useful if it could be obtained. If we consider, besides, that this metal exists in considerable proportions in nature, that its ore is argil [clay], we may well desire that it should become of general use. I have much hope that it may be so, for chloride of aluminium is decomposed with remarkable facility by common metals at a high temperature, and a reaction of this nature, which I am now endeavouring to realise on a larger scale than a mere laboratory experiment, will decide this question in a practical point of view." Not long after the above announcement was made, Sainte- Claire Deville, supported in the practical development of his ingenious pro- cess by the late Emperor of the French, succeeded in producing alu- minium in abundance, and bars of this useful metal entered the market as a commercial product to the great surprise and delight, not only of scientists, but of those workers in metals who know how to appre- ciate the importance of a metal possessing such remarkable character- istics as aluminium. "We all know now what an important position it has taken in the arts ; but its usefulness may yet receive further development, it is hoped, by some successful process of electro-depo- sition. That point, however, has not yet been fully reached, although the metal has been deposited with sufficient success to warrant the belief that still more satisfactory results will be obtained by a further investigation of the subject. Speaking upon the separation of aluminium by electrolysis, Deville observes:* " It appeared to me impossible to obtain aluminium by the battery in aqueous liquids. I should believe this to be an.impos- sibility if the brilliant experiments of M. Bunsen on the production of barium did not shake my conviction. Still, I must say that all processes of this description which have recently been published for the preparation of aluminium have failed to give me good results. It is of the double chloride of aluminium and sodium, of which I have already spoken, that this decomposition is effected. The bath is composed of 2 parts by weight of chloride of aluminium, with the addition of I part of dry and pulverised common salt. The whole is * " The Chemist," new series, vol. ii. p. 12, x855. 362 ELF.CTRO-DEPOSITION OP VARIOUS METALS. mixed in a porcelain crucible, heated to about 392 Fahr. The com- bination is effected with disengagement of heat, and a liquid is obtained which is very fluid at 392 Fahr., and fixes at that tempera- ture. It is introduced into a vessel of glazed porcelain, which is to be kept at a temperature of about 392 Fahr. The cathode is a plate of platinum, on which the aluminium (mixed with common salt) is deposited in the form of a greyish crust. The anode is formed of a cylinder of charcoal, placed in a perfectly dry porous vessel, contain- ing melted chloride of aluminium and sodium. The densest charcoal rapidly disintegrates in the bath and becomes pulverulent ; hence the necessity of a porous vessel. The chlorine is thus removed, with a little chloride of aluminium, proceeding from the decomposition of the double salt. This chloride would volatilise and be entirely lost, if some common salt were not in the porous vessel. The double chloride becomes fixed, and the vapours cease. A small number of voltaic elements (two are all that are absolutely necessary) will suffice for the decomposition of the double chloride, which presents but little resist- ance to the electricity. The platinum plate is removed when it is sufficiently charged with the metallic deposit. It is suffered to cool, the saline mass is rapidly broken off, and the plate replaced." Bunsen electrolysed the fused chloride of aluminium and sodium in a deep covered porcelain crucible, divided by a partition of porous porcelain, which extended half-way down the vessel. Carbon elec- trodes were used, and these were introduced through openings in the cover. He used a current from ten cells of his zinc and carbon battery. The salt fused at 662 Fahr. (the boiling point of mercury), and readily yielded the metal. The temperature of the liquid should then be raised to nearly the melting point of silver, when the particles of the liberated aluminium fuse, uniting together into globules, which, being heavier than the fused salt, fall to the bottom of the crucible. Corbelli has deposited aluminium by electrolysing a mixed solution of rock alum (sulphate of alumina) and chloride of sodium or calcium with an anode of iron wire, coated with an insulating material, and dipping into mercury deposited at the bottom of the solution ; a zinc cathode is immersed in the solution. Aluminium deposits upon the zinc, and the chlorine set free at the anode unites with the mercury, forming chloride of mercury (calomel). TJiomas and TUley's Process, for which a patent was obtained in 1854, consists in forming a solution composed of freshly precipitated alumina dissolved in a boiling solution of cyanide of potassium. By another process, patented in 1855, calcined alum is dissolved in a solution of cyanide of potassium. Several other solutions are included in the same specification, and the invention includes the deposition of DEPOSITION OF CADMIUM. 363 alloys of aluminium with silver, silver and copper with tin, silver and tin, &c. Jeancorfs Process (American) consists in depositing aluminium from a solution of a double salt of aluminium and potassium, of the specific gravity ri6i, employing a current from three Bunsen cells, the bath being worked at 140 Fahr. M. Bertrand states that he has deposited aluminium upon a plate of copper in a solution of the double chloride of aluminium and ammo- nium by using a strong current, the deposit being susceptible of a brilliant polish. Ooze's Process. Mr. Goze obtained a deposit of aluminium by the single cell method from a dilute solution of the chloride. The liquid was placed in a jar, in which was immersed 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 -coloured deposit 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 in the atmosphere, but was acted upon by dilute sulphuric and nitric acids. Deposition of Cadmium. This metal is readily soluble in dilute nitric, sulphuric, and hydrochloric acids, with disengagement of hydrogen, and the respective salts may be obtained in the crystalline form by concentrating the acid solutions by evaporation. The hydrated oxide, in the form of a gelatinous precipitate, is produced when a solution of the alkalies, soda, potassslf'&c., is added to a solution of a salt of cadmium. The hydrate is white, but becomes brown from loss of water when dried by heat. Respecting the electro -deposition of cadmium, Smee states that it is difficult to obtain firm, coherent deposits from solutions of the chloride or sulphate, but that it may be easily deposited in a reguline and flexible condition from a solution of the ammonio- sulphate, prepared by adding sufficient liquid ammonia to sulphate of cadmium to redissolve the precipitate at first formed. Napier recommends the following : " A solution of cadmium is easily prepared by dissolving the metal in weak nitric acid, and precipitating it with carbonate of soda, washing the precipitate, and then dissolving it in cyanide of potassium. A battery power of three or four pairs is required, and the solution should be heated to at least 100 Fahr. The metal is white, and resembles tin ; it is very soft, and does not present many advantages to the electro-metallurgist." Russell and W^oolrich's Process. This process, for which a patent was obtained in 1849, is thus briefly described: " Take cadmium, and dissolve it in nitric acid diluted with five or six times its bulk of water, 364 ELECTRO-DEPOSITION OF VARIOUS METALS. at a temperature of about 80 or 100 Fahr., adding the dilute acid by degrees until the metal is all dissolved ; to this solution of cadmium one of carbonate of sodium (made by dissolving i Ib. of crystals of washing soda in I gallon of water) is added until the cadmium is all precipitated ; the precipitate thus obtained is washed four or five times with tepid water. Next add as much of a solution of cyanide of potassium as will dissolve the precipitate, after which one -tenth more of the solution of the potassium salt is added to form free cyanide. The strength of this mixture may vary ; but the patentees prefer a solution containing six troy ounces of metal to the gallon. The liquid is worked at about 100 Fahr., with a plate of cadmium as an anode." For depositing cadmium M. A. Bertrand recommends a solution of the bromide of cadmium, containing a little sulphuric acid, or a solu- tion of sulphate of cadmium. He states that the deposit obtained is white, adheres firmly, is very coherent, and is capable of receiving a fine polish. Deposition of Chromium. In his 'investigation concerning the electrolysis of metallic salts Bunsen determined the causes which most influence the separation of the metal ; these pauses are two in number, the principal of which is owing to the density of the current, and the other to the greater or less concentration of the electrolyte. By density he means the concentration to a single point of " the elec- trical undulations, in a manner analogous to the concentration of luminous or calorific rays in the focus of a concave mirror. Let us take, for example, a charcoal crucible in communication with the positive pole of the battery, and place in it a small capsule of glazed porcelain, containing the liquid to be decomposed ; the space between the crucible and the capsule is filled with hydrochloric acid, and the liquid of the small capsule is put in communication with the battery by means of a thin sheet or wire of platinum.* The current is then established between a large surface, the charcoal crucible, and a fine platinum wire, in which it is concentrated ; the effects are added in this direction, and the fluid becomes capable of overcoming affinities which have hitherto resisted powerful batteries." The apparatus just described is placed in a porcelain crucible, which is kept warm in a sand bath. By the above arrangement Bunsen succeeded in separating chro- mium with perfect facility from a concentrated solution of its chloride ; the deposited metal, which was chemically pure, presented the ap- pearance of iron, but was less alterable in moist air. It resisted * For this purpose the platinum wire must be exactly in the centre of the crucible ; if not, by virtue of its tendency to take the shortest road, the current is established in preference between the nearest points. DEPOSITION OF MAGNESIUM. 365 the action of even boiling nitric acid, but was acted upon by hydro- chloric acid and dilute sulphuric acid. Bunsen found that when the current was diminished, the metal ceased to be deposited in the metallic state, but appeared as a black powder consisting of protoxide and sesquioxide of chromium.* Deposition of Manganium, or Manganese. The same eminent chemist succeeded in obtaining metallic manganese by the method above described from a concentrated aqueous solution of chloride of manganese. The metal was separated with the greatest facility with a powerful current, but when the current was weakened black oxide of manganese was obtained. Deposition of Magnesium. Bunsen electrolysed fused chloride of magnesium at a red heat by the same method as that adopted for the separation of aluminium. Manganese, being a very light metal, is liable to rise to the surface of the fused mixture and ignite in the air ; to prevent this, as far as possible, the carbon cathode was notched, so that the metal could collect in the notches. M. Bertrand says that from an aqueous solution of the double chloride of magne- sium and ammonium, a strong current will deposit magnesium upon a sheet of copper in a few minutes, the deposit being homogeneous, strongly adherent, and easily polished. Deposition of Silicon. Mr. Groze reduced the metal silicium from a solution of monosilicate of potash, prepared by fusing one part of silica with 2\ parts of carbonate of potash, the same voltaic arrange- ment being adopted, except that a small pair of Smee batteries were interposed in the circuit. With a very slow and feeble action of the current, the colour of the deposit was much whiter than aluminium, closely approximating that of silver. We have given the foregoing details concerning the deposition of some of the less tractable metals, more with a view to show what ingenious methods have been devised for their extraction, or separa- tion, than as presenting any absolute practical advantage. As inter- esting electrolytic facts they are valuable to the student, while to the more practical operator who may devote a portion of his spare time to electrolytic experiments, Chevalier Bunsen's methods of conducting the electrolysis of salts which do not readily yield up their metal from aqueous solutions will prove not only interesting but highly instruc- tive. It will not be in accordance with the object of this work, how- ever, to enter further into the deposition of metals which have no practical significance in the arts. * ''The Chemist," new series, vol. i, p. 685. CHAPTER XXVII. ELECTRO-DEPOSITION OF ALLOYS. Electro-deposition of Brass and Bronze. Brassing Solutions. Brunei, Bisson, and Co.'s Processes. De Salzede's Processes. Newton's Processes. Russell and Woolrich's Process. Wood's Process. Morris and Johnson's Process. Dr. Heeren's Process. Roseleur's Processes. Walenn's Pro- cesses. Bacco's Solution. Winckler's Solution. American Formulae for Brassing Solutions. Thick Brass Deposits. Brass Solution pre- pared by Battery Process. Electro-deposition of Brass and Bronze. The deposition of two metals in combination by electro -chemical means, although perfectly practical, is far more difficult to accomplish satisfactorily than to deposit a single metal. For example, the two metals zinc and copper are so widely different in all their characteristics in their melting point, ductility, electric relation, and conductivity that when in a state of solution great care is necessary to enable us to bring them together in the uniform condition of what is termed an alloy. Even when these two metals are alloyed in the ordinary way, by fusion, great care must be exercised, or the zinc, being a volatilisable metal, will pass away into the air instead of uniting with the copper to form brass. The copper, melting at a far higher temperature than zinc, is fused or melted first, and the zinc gradually added, until the desired object is obtained a bright yellow alloy, the tone or colour of which may be varied according to the proportion of either metal. In depositing brass from its solution, the nature and strength of the electric current are of the greatest importance, for if the electro- motive force be too weak copper only will be deposited, and if too strong zinc alone will be precipitated upon the receiving metal. Again, if too great a surface of anode be exposed in the bath in propor- tion to the size of the article to be coated zinc alone will deposit, the reverse being the case, that is copper alone, if the surface of anode is too small. A medium between these conditions is absolutely necessary (all other things being equal) to ensure a coating of brass of good colour upon any given article. To make this more clear to the less experienced, we may state, for instance, that a battery composed of the two elements, zinc and copper, as the Wollaston and Daniell batteries, ELECTRO-DEPOSITION OF BRASS AND BRONZE. 367 are far less intense, that is to say, they possess feebler electromotive force, than Bunsen's battery, with carbon and zinc elements. The latter battery, therefore, is more suited to the electro -deposition of brass, and is indeed preferable to any other. The quality of the deposit is also much influenced by the temperature of the solution and the materials with which it is prepared, some formulae yielding solutions which are better conductors than others, and consequently offer less resistance to the current. In making up solutions for the deposition of alloys, as brass, bronze, and German silver, for example, the author prefers to prepare them in what may be termed the direct way ; that is to say, instead of form- ing the depositing solution from a mixture of the metallic salts and their solvents, according to the usual method of preparing such solutions, he first dissolves the metallic alloy in its acid solvent nitric or nitro -hydrochloric acid (aqua regia) and from the acid solution thus obtained he forms the depositing bath by either of the methods given below. It may be well to remark, however, that in making up a brass bath upon this system, metal of the very best quality should be employed, and the solution should be formed from the identical sample of brass which is to be used as an anode in the depositing tank. The proportions given are for one gallon of solution, but it will be readily understood that, adopting the same proportions of the materials, a bath of any desired quantity can be prepared. Brassing Solutions. No. /.Take of Good sheet brass . . . . . . i ounce. Nitric acid (by measure) about . . .4 ounces. Water . . . . . >\' 4 . 2 Cut up the sheet brass into strips, and put them carefully into a glass flask, then pour in the water and acid. To accelerate the chemical action the flask should be gently heated over a sand bath, and the fumes must be allowed to escape through the flue of the chimney. When the red fumes, liberated during the decomposition, cease to be visible in the bulb of the flask the chemical action is at an end, pro- vided a portion of undissolved brass remains in the flask. If such be not the case a few fragments of the metal should be put into the flask and the heat continued, when, if red fumes are again given off, the heat should be kept up until the fumes disappear while a portion of undissolved metal still remains in the flask. The reasons for giving these precautionary details are I, that it is important there should be as little excess of acid as possible in the solution ; and 2, that the strength of commercial nitric acid is very variable, and therefore chemically minute proportions cannot advantageously be given. We may say, moreover, that the exact quantity of brass per gallon of solu- 368 ELECTRO-DEPOSITION OF ALLOYS. tion is of no consequence ; if the proportion nearly approaches that given in the formula, it will be quite near enough for all practical purposes. While touching upon this subject we may also state that the active quality of commercial cyanide of potassium also varies greatly ; consequently it may be necessary to apply either more or less than the quantity specified below, according to the quality of the article that may fall into the hands of the user. Upon this subject we Bhall, however, say more hereafter. The acid solution of brass must next be poured into a vessel of sufficient capacity, and diluted with about three or four times its bulk of water. Then add liquid ammonia (specific gravity '880), gradually to the green solution of the metals, stirring with a glass rod, when a pale green precipitate will be formed, which will afterwards become dissolved by adding an excess of ammonia, forming a beautiful deep blue solution. This solution should become perfectly clear when the necessary quantity of ammonia has been added, but if such be not the case, a little more must be added, with brisk stirring, until the precipitate is quite dissolved and a clear solution obtained. The exact quantity of ammonia required will depend upon the amount of free acid remaining in the metallic solution first prepared. A moderately strong solution of cyanide must now be added to the blue solution, with constant stirring, until the blue colour entirely disappears. When sufficient cyanide has been added to destroy the blue colour, the solution will acquire a pinkish tinge, and on the application of a little more cyanide solution this will in its turn disappear, and the liquid will assume a yellowish tint, when a moderate excess of the cyanide must be given as " free cyanide," and the solution then made up to the full quantity (one gallon) by the addition of water. The solution should then be set aside to rest for a few hours, when the clear liquor may be poured into the depositing vessel. The last portion of the liquor should be passed through a filter, to separate any im- purities (chiefly derived from the cyanide) which may be present. If convenient, the entire bulk of the solution may be filtered, which is in all cases preferable. A brassing bath always works most satisfactorily if not used for at least twenty-four hours after being prepared, although it may, if required, be used directly after being filtered. If to be used hot, the solution may be further diluted. Solution II. One ounce of brass being dissolved as before, the solution is to be diluted with about three pints of cold water ; a solu- tion of carbonate of potash (about half -a -pound to a quart of water) is to be gradually added, with frequent stirring, until no further pre- cipitation takes place. The precipitate formed should next be put into a filter of unbleached calico stretched over a wooden frame, and when the liquor has ceased to drain from it, hot water should be BEASSING SOLUTIONS. 369 poured on to the mass, which must be stirred with a wooden spoon, or flat strip of wood, so as to assist the washing of the precipitate with the water. When the precipitate is thoroughly drained, it is to be transferred to a convenient vessel, and redissolved by liquid ammonia, which is to be added gradually, and constantly stirred in until the whole is dissolved, and a dark blue solution formed. After reposing for a few minutes, Hhe clear liquor may be poured off, and should any undissolved green precipitate remain at the bottom of the vessel, ammonia must be added to this until dissolved, when the resulting blue liquor is to be added to the bulk. A strong solution of cyanide is now to be added to the blue liquor, until its characteristic colour has entirely disappeared, after which a moderate excess of the cyanide solution is to be added, and the solution then made up to I gallon (according to the proportion of metal dissolved) with cold water. The repose or nitration as before should be again resorted to. Solution III. Acetate f copper . . ..... 5 ounces, Sulphate of zinc . . ... .10 Caustic potash . , ....'.'.. 4^ Ibs. Liquid ammonia . . . . . . i quart. Cyanide of potassium . . . . .8 ounces. The acetate of copper should be first powdered, and then dissolved in about 2 quarts of water. To this add one-half of the ammonia (i pint). Now dissolve the sulphate of zinc in I gallon of water at a temperature of 180 Fahr. ; to this add the remaining pint of the ammonia, constantly stirring while the liquid is being added. The potash is next to be dissolved in i gallon of water, and the cyanide in i gallon of hot water, after which the several solutions are to be mixed as follows : The solutions of copper and zinc are to be first mixed, the solution of potash then added, and lastly the cyanide. The whole must now be well stirred, and then allowed to repose for a short time, when the agitation may be resumed and repeated at intervals during a couple of hours or so. Water, to make up 8 gallons in all, is now to be added, and the solution then allowed to rest for a few hours, when the clear liquor is to be decanted into the bath. This solution should be worked with a strong current, with additions of liquid am- monia and cyanide from time to time when the anode becomes foul. Jt is important in working this, as in all other brassing solutions, that the anode should be kept clean, a condition which is not possible with these solutions unless there be an excess of the solvents, cyanide and ammonia. Brunei, Bisson, & Co.'s Processes. I. The brassing solution is formed from the following ingredients, which should each be dissolve! in separate vessels ; 3B 370 ELECTRO-DEPOSITION OF ALLOYS. Carbonate of potassa (salt of tartar) . . 10 pounds. Cyanide of potassium . . . . . i| pound. Sulphate of zinc i J Chloride of copper . . . . . 10 ounces. Water 12^ gallons. A sufficient quantity of the potash solution is to be added to the sul- phate of zinc and chloride of copper solutions to precipitate all the metal in the form of carbonates. Liquid ammonia (specific gravity 880) is now to be poured into each vessel, being well stirred in to dissolve the respective precipitates, when the solutions are to be added to the cyanide solution ; the remainder of the potash solution is next to be added, and the whole well stirred ; water is then to be added to make up a bath of I2| gallons. The solution is to be worked with two or more Bunsen batteries, with a large brass anode. As before recommended, the solution should not be worked until some hours after being made, and the clear liquid must be decanted, so as to separate it from any sedimentary matter that may be present from impurities in the cyanide or otherwise. After using the bath for some time, it will require moderate additions of cyanide and liquid ammonia, to keep the anode free from the white salt of zinc which forms upon its surface when the excess of these substances has become exhausted. In adding fresh cyanide, a portion of the solution may be taken out of the bath with a jug, and a few lumps of cyanide (say half a pound) added, and as this becomes partially dis- solved, the liquid is to be added to the bath, and the jug again filled with the solution as before ; in this way the bath may be strengthened with cyanide without employing water to dissolve it. In warm weather, however, when the bath loses water by evaporation, the cyanide may be dissolved in water before adding it to the bath When either liquid ammonia or cyanide are to be added to the solu- tion, this may be conveniently done overnight, and the bath well stirred, when by the following morning the disturbed sediment, which always accumulates at the bottom of depositing vessels, will have had time to settle. Solution 2. This is prepared from the following ingredients : Sulphate of zinc . . . . .2 pounds. Chloride of copper . ... . i pound. Carbonate of potassa . . . . -25 pounds. Nitrate of ammonia ..... 12^ The chloride of copper is to be dissolved in half a gallon of water, the carbonate of potash in 6 gallons of water, and the sulphate of zinc in half a gallon of hot water. These three solutions are now to be mixed, and the nitrate of ammonia added, when the whole are to be well united by stirring. Sufficient water is next to be added to NEWTON'S PEOCESSES. 371 make up about 20 gallons of solution, which must be allowed to rest for some hours before using it. After working this solution for some time it will be necessary to add moderate quantities of liquid ammonia and cyanide of potassium, otherwise the anode will become foul and thus incapable of becoming dissolved in the solution.. De Salzede's Processes. I. This is prepared from the following formula : Cyanide of potassium . . . . .12 parts. Carbonate of potassa 610 Sulphate of zinc . ..'.. . 48 Chloride of copper . ''... . . 25 Nitrate of ammonia 305 Water 5000 The cyanide is to be dissolved in 120 parts of the water, and the car- bonate of potash, sulphate of zinc, and chloride of copper are next to be dissolved in the remainder of the water, the temperature of which is to be raised to about 150 Fahr. When the salts are well dissolved, the nitrate of ammonia is to be added, and the mixture well stirred until the latter is all dissolved. The solution should be allowed to stand for several days before using, and. the clear liquor separated from any sediment that may have deposited at the bottom of the vessel. Solution 2. Cyanide of potassium "... 50 parts. Carbonate of potassa 500 Sulphate of zinc 35 Chloride of copper 15 Water 5000 This solution is to be made up in the same way as No. i. Solution 3. Bronzing Solution. : This solution is the same as No. I, except that 25 parts of chloride of tin are substituted for the sulphate of zinc. Solution 4. Bronzing Solution. This solution is the same as No. 2, with the exception that 12 parts of chloride of tin are substituted for the sulphate of zinc. This solution is worked warm, that is, at about 97 Fahr. Newton's Processes consist in forming solutions for depositing brass or "bronze. He mixes chloride of zinc with the chloride of ammonium (sal-ammoniac), chloride of sodium (common salt), or chlo- ride of potassium, dissolved in water. Or he makes a mixture of acetate of zinc dissolved in water and acetate of ammonia, soda, or potassa. In making up a brassing solution, Newton adds to either of the above solutions a proportion of the corresponding salt of copper : for example, with the acetate of zinc he would unite acetate of copper, 372 ELECTRO-DEPOSITION OF ALLOYS. and so on. In making a bronzing solution, he dissolves the double tartrate of copper and potassa, and double tartrate of the protoxide of tin and potassa. He deposits an alloy of zinc, tin, and copper by employing a solution composed of the following : double cyanide of copper and potassium, "zincate " of potassa, and stannate of potassa. The zincate of potassa, he forms by fusing oxide of zinc with caustic potassa, and the stannate of potassa, either by fusing oxide of tin with caustic potassa, or by dissolving it in a solution of potassa. To form a brassing bath, he also employs a solution consisting of a given quantity of oxide of copper dissolved in an excess of cyanide of potassium ; oxide of zinc and a little liquid ammonia are then added, and the solution heated from 120 to 140 Fahr. Water is then added to allow the solution to contain 3 ounces of the metallic oxides to each gallon of the solution, that is, 2 ounces of zinc oxide to I ounce of copper oxide, being the proportions to- form brass. Russell and Woolrich's Process. A solution is made of the following : Acetate of copper .10 pounds. zinc . .... i pouud. potassium 10 pounds. Water .*..:.... 5 gallons. The salts are to be dissolved in the water, and as much of a solution of cyanide added as will first precipitate the metals, and afterwards redissolve the precipitate. An excess of cyanide is then to be added, and the solution set aside to settle as before. A brass anode, or one of zinc and another of copper, may be used. Wood's Process consists in making a solution as follows : Cyanide of potassium (troy weight) . . . i pound. copper 2 ounces. zinc i ounce. Distilled water i gallon. When the ingredients are dissolved, add 2 ounces of sal-am- moniac. For coating smooth articles, it is recommended to raise the temperature of the solution to 160 Fahr., using a strong current. Morris and Johnson's Process. A solution is made by dissolv- ing in i gallon of water Cyanide of potassium . , . . i pound. Carbonate of ammonia i Cyanide of copper . . . . ' . .2 ounces. zinc i ounce. The solution is to bo worked at a temperature of 150 Fahr., with a large brass anode, and a strong current. DE. HEEEEN'S PEOCESS. 373 Dr. Ileeren's Process. According to this authority,* a brassing solution may be prepared by employing a large excess of zinc to a very small proportion of copper, as follows : Take Sulphate of copper . . . . i . i part. zinc 8 parts. Cyanide of potassium 18 The ingredients are to be dissolved in separate portions of warm water. The copper and zinc solutions are now to be mixed, and the cyanide solution then added, when 250 parts of distilled water are to be added, and the mixture well stirred. The bath is to be used at the boiling temperature, with two Bunsen cells. By this process it is said that very rapid deposits of brass have been obtained upon articles of copper, zinc, Britannia metal, &c. Roseleur's Processes. I. Dissolve in 1,000 parts of water, 25 parts of sulphate of copper and from 25 to 30 parts of sulphate of zinc ; or, 12 J parts of acetate of copper and \2\ to 15 parts of fused chloride of zinc. The mixture is to be precipitated by means of 100 parts of carbonate of soda previously dissolved in plenty of water, with constant stirring. The precipitate is to be washed several times, by first allowing it to subside and then pouring off the supernatant liquor (which may be thrown away), when fresh water is to be poured on the precipitate, and after again stirring it is allowed to subside, the washing to be repeated two or three times. After pouring off all the water the last time, a solution composed of 50 parts of bisulphide of sodium and 100 parts of carbonate of soda dissolved in 1,000 parts of water, is to be added, stirring well with a wooden rod. A strong solution of commercial cyanide of potassium is now to be added until the precipitate becomes just dissolved. From 2\ to 3 parts of cyanide in excess are now to be added with stirring, when the solution is complete. Solution 2. To form a cold bath for brassing all metals, dissolve 15 parts of sulphate of copper and 15 parts of sulphate of zinc in 200 parts of water ; now add a solution made by dissolving 40 parts of carbonate of soda in 100 parts of water, and stir the mixture well. The precipitate is allowed to subside, as before, when the clear liquor is to be run off, and fresh water added, to wash the precipitate, the washing to be repeated several times. To the drained precipitate add 20 parts of bisulphide of sodium dissolved in 900 parts of water. Now dissolve 20 parts of cyanide of potassium and two -tenths of a part of arsenious acid (white arsenic) in 100 parts of water, and add this to the former liquor. This decolours the mixture and completes the * * The Chemist," 1855, p. 345. 374 ELECTRO-DEPOSITION OF ALLOYS. brassing solution. The effect of the arsenious acid is to render the deposit bright. "We were long accustomed to employ small quantities of white arsenic with our brassing solutions, and when used with moderation considered the addition highly favourable to a good deposit of brass. Roseleur recommends, in working this bath, to add a little cyanide when the deposit looks earthy, or ochreous, and arsenic when it yields a dull deposit ; if too red, a little zinc and cyanide are to be added ; if too white, a little copper and cyanide ; if the solution works tardily, add both zinc and copper salts, and more cyanide ; and since the anode does not dissolve freely enough to keep up the strength of the solution, these additions of the metallic salts and cyanide must be made from time to time whenever the bath works tardily. The same remedy should be applied to all brassing solutions when they work sluggishly. When the above solution, by the additions of the metallic salts, reaches a higher specific gravity than 1-091, water must be added, but the specific gravity must not be lower than i -036. Solution 3. The following solution is recommended for coating steel, cast iron, wrought iron and tin : Dissolve 2 parts of bisulphite of soda, 5 parts of cyanide of potassium (of 75 per cent.), and 10- parts of carbonate of soda in 80 parts of distilled water, and add to the mixture i part of fused chloride of zinc and i parts of acetate of copper, dissolved in 20 parts of water. Solution 4. For coating zinc articles, the following solution is recommended : 20 parts of bisulphite of soda and 100 of cyanide of potassium (of 75 per cent.) are dissolved in 2,000 parts of water. Then dissolve 35 parts of chloride of zinc, 35 parts of acetate of copper, and 40 parts of liquid ammonia in.soo parts of water. The solutions are now to be mixed and the compound solution passed through a filter. In working these solutions, if too strong a current be employed, or too large a surface of anode exposed in the solution, zinc only will be deposited ; if the current be feeble, or if the articles are kept in motion while deposition is taking place, the deposit will be chiefly or wholly copper. If a white deposit of oxide of zinc appears upon the anode, a small quantity of liquid ammonia should be added to the bath. Walenn's Processes. A solution for depositing brass is made as follows : Crystallised sulphate of zinc i part, and crystallised nitrate of copper 2 parts, are dissolved to saturation. Strong liquid ammonia is then added in sufficient quantity to precipitate the oxides and redis- solve them. Cyanide of potassium is then added until the purple liquid is completely decoloured. The resulting solution should be left to repose for a day or two, and may be worked w.ith from i to 3 Smee cells, using heat if a brass anode be employed. It is preferred, how- WALENN S PKOCESSES. 375 ever, to work the solution by a ' ' porous cell arrangement, in which the surface of the solution next the zinc or other dissolving plate is at a greater elevation than that of the external or depositing solu- tion." In working the solution, the hydrated oxides of copper and zinc are added from time to time, and, if necessary, ammoniuret of copper also. For a hot brassing solution, "Walenn gives the following formula : A " solvent solution " is first made, consisting of Cyanide of potassium (standard solution) . . 6 parts. Nitrate of ammonium . , i part. Sulphate of . 2 parts. The standard solution of each salt consists of the solid salt dissolved in five times its weight of water. The ingredients being mixed, the whole^is divided into three parts : Free solvent solution ...... i part. Solution to dissolve cupric cyanide . . 5? parts. zinc . 2! When the respective cyanides have been dissolved to saturation in the above proportions, the free solution is added, and the whole well mixed ; ammoniuret of copper is then added, and the solution set aside for a day or two. "Walenn prevents the evolution of hydrogen (or nearly so) during deposition by adding the hydrated oxides of copper, or ammoniuret of copper and zinc, in sufficient quantity for the purpose. By another process he employs solutions of cyanide of potas- sium and tartrate of ammonium, in equal proportions. In this menstruum he dissolves cyanides, tartrates, carbonates, &c. of copper and zinc, and the solutions thus formed may be worked either hot or cold. The proportions of the various salts must be varied according to the strength of the current employed. Walenn makes the following observations on the electro -deposition of copper and brass : "A solution containing one pound of cupric sulphate, and one of sulphuric acid to a gallon of water, deposits the metal in a solid and compact mass, with a somewhat botryoidal* surface. The addition of one ounce of zinc sulphate (as recommended by Napiqr) prevents this botryoidal form, and renders the deposit tough, compact, and even. From a solution containing a greater proportion of zinc, sulphate copper is deposited in tufts or needles, * Botryoidal, resembling a bunch of grapes ; referring to the nodular or knotty form which copper assumes at the back of electrotypes. 376 ELECTRO-DEPOSITION OF ALLOYS. standing at right angles to the surface of the metal. Ordinary- electro -brassing liquids [deposits from] show the same peculiarity in even a more marked degree, and this makes it impossible to produce a good deposit of more than 'Oi to "03 inch in thickness. This form of deposit is owing chiefly to a copious evolution of hydrogen taking place during its formation." While not disagreeing with Mr. Walenn's views, the author may state that he has found that a small quantity of arsenious acid (previously mixed with a strong solution of cyanide) added to brassing baths had generally rendered the deposit smooth and compact ; the quantity, however, must be small, other- wise the deposit is liable to be of a brittle character. About one drachm of arsenious acid to each gallon of bath will be sufficient. He has usually noticed that brassing solutions evolve hydrogen most freely when poor in metal, and when containing a large excess of cyanide. A solution richer in metal, and containing but a moderate excess of cyanide, generally yields better results, both as to colour and general character of the deposit. A great deal depends, however, upon the amount of current and its tension, and also upon the tem- perature of the bath. A solution rich in copper and zinc is best worked at about 130 Fahr., or even higher. When the solution becomes partly exhausted of its metals, owing to the brass anodes not becoming freely dissolved in the solution, it is always advisable to add fresh concentrated cyanide solutions of the zinc and copper salts from time to time, taking care, however, only to add them in sufficient quantity to obtain the desired effect a coating of good colour with but trifling evolution of hydrogen at the negative electrode. Baeco's Solution. The following solution is said to yield a brass deposit upon zinc work that will stand burnishing, and the deposit may be obtained either by simple immersion or by the battery. A solution is first prepared by dissolving equal parts of sulphate of zinc and sulphate of copper in water. A strong solution of cyanide of potassium is then added in sufficient quantity to redissolve the pre- cipitate formed ; to the resulting solution one -tenth to one -fifth of liquid ammonia is added, and the solution is then diluted with water until it stands at about 8 Baume. For a light -coloured deposit of brass 2 parts sulphate of zinc to I part sulphate of copper are used. In adding cyanide to the solution of the sulphates, great care must be taken to avoid inhaling the cyanogen fumes that are liberated, which are highly poisonous. A solution of this character should only be prepared by a person well accustomed to chemical manipulations. Winckler's Solution. Saturated solutions of chloride of zinc and sulphate of copper are first prepared, in separate vessels. A solution of cyanide of potassium, consisting of cyanide 100 parts in water 1,000 parts, i.s next prepared, and this is added to the solution of BRASS SOLUTION FOB ROUGH CAST-IRON. 377 sulphate of copper until the precipitate at first formed is redissolved, when a grass-green liquid results ; into this the solution of zinc is gradually introduced, with constant stirring, until the solution exhibits a white turbidity. The solution is then diluted with 2,000 parts of water, and heated to the boiling point in an enamelled vessel, and then allowed to cool. It is next filtered, when it is ready for use. The bath is worked at the ordinary temperature, with a brass anode. Brass Solution for Rough Cast Iron. The following formula has been given for brassing cast-iron work, and is said to yield a good colour : Soft water -. . . . . . . 14 pints. Bisulphite of soda . v, .., *.-.- . 7 ounces Cyanide of potassium .., ,. . < ... . 17 Carbonate of soda . ,...',, . 34 To which is added Acetate of copper . . . . . 4 ounces. Neutral chloride of zinc 3^ Water 3^ pints. American Formulae for Brassing Solutions. The Scientific American publishes the following formulae for brass solutions: I. When the ordinary commercial cyanide is employed, the following ia said to answer very well : Sulphate of copper 4 ounces. Sulphate of zinc 4 to 5 Water i gallon. Dissolve and precipitate with 30 ounces of carbonate of soda ; allow to settle, pour off the clear liquid, and wash the precipitate several times in fresh water. Add to the washed precipitate Carbonate of soda 15 ounces. Bisulphite of soda . . . . 7$ Water i gallon. Dissolve the above salts in the water, assisting the solution by con- stant stirring ; then stir in ordinary cyanide of potassium until the liquid becomes clear and colourless. Filter the solution, and to im- prove its conductivity, an additional half -ounce of cyanide may be given. Cold Bath for all Metals. Carbonate of copper (recently prepared) . . 2 ounces. zin c 2 soda 4 37$ ELECTRO-DEPOSITION OF ALLOYS. Bisulphite of soda 4 ounces. Cyanide of potassium (pure) . . . . 4 Arsenious acid , . 3 1 ,, Water i gallon. Dissolve, precipitate, and redissolve as before, and filter if necessary. The arsenious acid is added to brighten the deposit ; an excess is apt to give the deposited metal a greyish -white colour. Thick Brass Deposits. MM. Person and Sire patented a process for obtaining stout coatings of brass upon steel or iron by depositing alternate layers of zinc and copper upon the objects, and then submitting them to heat until the metals become alloyed with each other. Brass Solution Prepared by Battery Process. A brassing solution may be prepared by the battery method by suspending a large brass anode in a strong and warm solution of cyanide of potas- sium, to which liquid ammonia is added; about i^ pound of good cyanide and 10 ounces of strong liquid ammonia to the gallon of water will be about the best proportions. A strong current must be employed. Some persons recommend the addition of hydrocyanic acid ; this will not be necessary if good cyanide be used. In preparing solutions by the battery process, or indeed by the ordinary chemical methods, it is far better to employ really good cyanide of a guaranteed strength than to call in the assistance of hydrocyanic acid, which, even in the most careful hands, is a hazardous substance to deal with in what may be termed practical quantities. All the best results in electro-deposition have been obtained without the direct aid of this volatile and highly -poisonous acid, and its employment should never be attempted by inexperienced persons under any circumstances whatsoever. CHAPTER XXV1IJ. ELECTRO-DEPOSITION OF ALLOYS (continued). Electro-brassing Cast-iron Work. Scouring. Electro-brassing Wrought-iron Work. Electro-brassing Zinc Work. Electro-brassing Lead, Pewter, and Tin Work. Observations on Electro-brassing. Bronzing Electro- brassed Work. French Method of Bronzing Electro-brassed Zinc Work. Green or Antique Bronze. Bronze Powders. Dipping Electro-brassed Work. Lacquering Electro-brassed Work. Electro-deposition of Bronze. Electro-deposition of German Silver. Morris and Johnson's Process. Deposition of an Alloy of Tin and Silver. Deposition of Alloys of Gold, Silver, &c. Deposition of Chromium Alloys. Slater's Process. Deposition of Magnesium and its Alloys. Alloy of Platinum and Silver. New White Alloys. Notes on Electro-brassing. Electro -brassing Cast-iron Work. Owing to the porous nature of this class of work, and its liability to present certain unavoidable defects of casting known as sand -holes, the articles to be coated with brass require to be prepared with some care before being immersed in the depositing bath. Moreover, it is necessary to remove the coating of oxide from the surface of the work previous to submitting the articles to the processes of scouring or cleaning. Cast-ironwork should first be placed in a " pickle " composed of the following mix- ture, in sufficient quantity for the work in hand : Sulphuric acid J pound. Water i gallon. The articles being placed in the above pickle are allowed to remain therein for about twenty minutes to half an hour, when they are taken out, one at a time, and examined ; if the oxide has become sufficiently loosened to readily rub off with the fingers, the articles are to be at once placed in clean cold water to rinse them ; they are then to be scoured with a hard brush, coarse sand, and water. If after rinsing any black oxide obstinately refuses to be brushed away, the work must be returned to the pickle for a short time longer, or until the objectionable matter readily yields to the brush, leaving a clean surface beneath. Some articles require but a short immersion in the acid pickle, while others need a much longer steeping. When the 380 ELECTRO-DEPOSITION OF ALLOYS. articles are coated with rust (oxide of iron) this may be removed by brushing them over with strong hydrochloric acid, after which they should be immersed in the sulphuric acid pickle until it is found that sand and water, applied with a very hard brush, will clean them. A solution for brassing cast-iron work should be very rich in metal. Scouring. When the articles are sufficiently pickled, they are to be removed from the bath and well rinsed in clean water ; they are then taken to the " scouring tray," and being placed on the horizontal board, are to be well rubbed with the hard brush, and coarse sand moistened with water, until they are perfectly bright and clean and free from all traces of oxide on their surfaces. They are now to be thoroughly rinsed in clean water, and are then ready for the brassing - bath. Some operators prefer to give them a momentary dip in a weak and cold potash bath, and then rinse them before placing the articles in the depositing bath. The work should be suspended in the bath by stout copper wires, and in the case of large pieces of work several such slinging wires should be employed, not only to give support to the articles, but to equalise, as far as possible, the action of the current ; since it must be remembered that cast iron is but an indifferent conductor as compared with other metals. Electro-brassing Wrought-iron Work. This class of work is more readily coated with brass (and copper) than the former, the metal being less porous and the articles generally in a smoother con- dition. The work is first to be pickled as before, and afterwards well scoured with sand and water, and then rinsed. The solution in which wrought-iron goods are brassed may have rather less metal (that is, zinc and copper) than is necessary for cast iron. When the articles have been in the bath a few moments, they should be tinted with the characteristic colour of brass. If, however, the colour is of too red a tone (showing an excess of copper in the deposit) the brass anode should be lowered a little further into the solution until the deposit is of the proper colour. If, on the contrary, the deposit is pale, or whitish (indicating an excess of zinc), the anode must be raised out of the solution to a slight extent. By regulating the anode surface in solution the colour of the deposit may be greatly varied ; the current of electricity must also be regulated according to the surface of work in the bath and the character of the metal to be coated cast iron, for example, requiring a current of greater electromotive force than wrought iron. Electro -brassing Zinc Work. This metal receives the brass deposit very freely, and the articles made from it are generally pre- pared for the bath with very little trouble as compared with iron work. Zinc goods should first be steeped in a pickle composed of dilute sulphuric acid, or the following mixture : ELECTEO-BKASSING ZINC WORK. 381 Sulphuric acid i ounce. Hydrochloric acid 2 ounces. Water :/-<"/*-" x gallon. The work should be immersed in the above bath from ten to twenty minutes, then well rinsed, and next scoured with a hard brush, silver sand, and water ; after being again rinsed, the article is to be immersed in the brass bath, and it will generally become coated all over in a few moments, providing the bath be in good condition, the current of sufficient power, and the proper surface of anode exposed in the solu- tion. If the deposit does not take place within a few seconds after immersion, the anode should at once be lowered in the bath until the yellow colour has struck well over the article, after which it may te again raised, and the operation then allowed to proceed, ur disturbed, until a coating of sufficient thickness is obtained. Since this class of work is not generally required to be subjected to friction (being chiefly castings of an artistic or ornamental character) a stout coating of brass is unnecessary ; moreover the zinc work, when electro -brassed, is usually required either to be bronzed, electro -gilt, lacquered, or finished in some other way. Zinc and iron articles should not be suspended in the bath at the same time if it be possible to avoid it ; if, however, this rule cannot be conveniently followed, the iron articles should enter the bath first, and when these have become coated with brass the zinc work may then be introduced. When zinc goods have received the required deposit, they should be well rinsed in hot but not boiling water, and then placed in hot mahogany or boxwood sawdust. After being well brushed with a soft, long-haired brush to remove the sawdust, the piece of work should be rubbed with a clean diaper or chamois -leather, and may then be lacquered or bronzed, as desired. If the article is required to be gilt, it is to be simply well rinsed after removing from the bath, and at once placed in the gilding bath. Electro-brassing Lead, Pewter, and Tin Work. Brass does not deposit upon lead so readily as upon zinc ; but pewter, however, receives the deposit pretty freely. Lead and pewter articles should be pickled for about half an hour in a dilute solution of nitric acid, consisting of about eight ounces of the acid to each gallon of water, then scoured with silver sand and water, a soft brush being employed. They are then to be rinsed and placed in the brass bath, a rather large surface of anode being immersed in the solution when they are first suspended. The current should be strong, otherwise lead is very apt to receive the coating only in parts. It is also best to employ a warm solution for brassing lead and pewter, but more especially the former. Articles of tin, or tinned iron articles, should also be brassed in a warm 382 ELECTRO -DEPOSITION OF ALLOYS. solution, and treated in other respects in the same way as the former metals, except that the preliminary pickling (which is not absolutely necessary in either case) may be dispensed with. Stereotype-plates may advantageously receive a deposit of brass, and, indeed, this method of producing a hard surface upon these plates has been to some extent adopted, a warm brassing solution being employed, with a strong current. For plates which have to be used for printing with vermilion ink neither a brass nor a copper facing should be adopted, since this colour, being a mercury preparation, would be liable to attack both the copper and its alloy (brass), and thus not only injure the metal facing, but also affect the colour of the ink itself. Observations on XHactro-brassing. After an electro -brassing bath has been used for some time, its whole character becomes greatly changed, unless, indeed, it has been worked under exceptionally favourable conditions, and even with such advantages it will invariably yield results far different from those at first obtained. There are several causes for this, and when these are fully understood it will be more readily seen how tolerable uniformity of action may be secured, absolute uniformity being, so far as we are aware, impossible in the deposition of this or any other alloy. The principal causes of change in the condition of brass deposits are (i) The anode, being composed of two metals of unequal solubility in cyanide of potassium, does not become freely and uniformly dissolved in the solution, consequently the latter becomes partially, and indeed greatly, deprived of its metallic constituents ; (2) If an excess of ammonia be employed as one of the solvents, this volatile substance by constantly evaporating alters the condition of the bath in proportion to its volatilisation ; (3) The oxide of zinc eliminated at the brass anode being less soluble than the oxide of copper evolved at the same electrode, the free cyanide in the solution is largely taken up by the latter to the exclusion of the less soluble zinc oxide, and as a consequence this latter substance hangs upon the surface of the anode, or falls to the bottom of the bath as an undissolved mass. In this way the solution becomes more freely supplied with copper than with zinc, and therefore becomes altered from its original condition ; (4) When a current of low electro -motive force is used in depositing brass, the copper of the alloy is more readily deposited than the zinc, which requires a current of higher electro- motive force than copper for its deposition, and as a consequence the solution soon becomes altered in its constitution. For example, when a Bunsen battery is employed in the deposition of this alloy, a very good quality of brass is obtained from a well-made brassing solution ; if for this battery a single "Wollaston battery were substituted, all other conditions being the same, copper alone would be deposited on the cathode ; (5) The amount of anode surface immersed in solution in OBSEKVATIONS ON ELECTED -BRASSING. 383 proportion to that of the cathode affects the deposition of brass in a sensible manner. To illustrate this, a very important lesson may be learnt in a very simple way : Take a small steel article, say a pocket latch-key, for example, and connecting it with the negative electrode of a Bunsen battery, suspend it in the brass bath, having previously immersed a large surface of the brass anode. "We shall at once observe that a deposit of zinc only has taken place upon the key. Let the key be scratch-brushed, and the anode raised out of the bath so that only a very small portion of one of its corners remains in the solution ; if now the key be suspended in the liquid we shall soon observe that it becomes coated with copper only. If the anode be now cautiously lowered in the bath, we find that the coating gradually assumes the characteristic colour of brass ; and if we take care to estimate the approximate amount of anode surface which yields the yellow alloy, we may in this way form a tolerable notion of the sur- face of this electrode which it is necessary to expose to a given surface of cathode with the electric power employed. As a further illustration of the caprice which attends the deposition of brass from its solutions, we have known instances in which a steel rod suspended horizontally in the bath has exhibited the following varieties of deposit : at one end zinc alone was deposited ; at the opposite end, copper ; and midway between the two, brass of various tints, from pale straw or lemon colour to a rich golden yellow. Motion also affects the character of the deposit, copper being deposited instead of brass when a brisk motion is given to the article while in the bath. When a much-used bath has a tendency to deposit copper alone, from the cause above stated, its condition may be improved in several ways (i) By adding liquid ammonia to dissolve the deposited oxide of zinc ; (2) By adding a strong cyanide solution of zinc until the required yellow deposit is obtained ; and (3) By syphoning off the clear solution, and adding ammonia to the deposit at the bottom of the depositing vat, and then returning the clear liquor, when after a few hours' repose the bath will generally work well. A moderate addition of cyanide may also be necessary. When it is found that the bath exhibits general signs of weakness owing to the anode failing to keep up its metallic strength, an addition of a concentrated solution of the metals, copper and zinc, must be made, in which there should be an excess of the metal most needed to bring the bath up to its proper condition. In working brassing solutions, it is always advisable to keep in hand a quantity of very concentrated brass solution, so that this may be added to the bath from time to time as required, and thus prevent the annoyance which attends the working of a sluggish and defective solution. Another way of strengthening an exhausted bath is the following : Take a large porous cell, and about three parts 384 ELECTRO-DEPOSITION OF ALLOYS. fill it with a strong solution of cyanide of potassium ; now connect a long and broad strip of copper to the negative pole of the battery ; immerse the porous cell in the brassing bath, either by standing it upright or by suspending it, according to the depth of the vessel. Now connect a large brass anode to the positive pole of the battery, and allow the current to pass through the solution for a few hours, by which time it will have taken up a considerable amount of brass if the current was sufficiently strong. Two or more 3 -gallon Bunsen cells should be employed for a loo-gallon bath of brass solution. K^a white deposit appears upon the brass anode, liquid ammonia should be added and well stirred into the solution. Bronzing Electro-brassed Work. By the term bronzing is meant the application of one or other of the numerous methods of staining brass, or imparting to the metal an antique or artistic appearance. When the electro -deposited metal is required to assume the appearance of solid brass, the process of lacquering is applied ; but for cast zinc or iron work electro-brassed, another system of ornamentation is adopted, which is known by the name of bronzing. For example, if a dilute solution of chloride of platinum be brushed over a brass surface, a black stain is produced, the depth or tone of which may be heightened by a second application of the solution. In this case the metal platinum is reduced by electro -chemical action, and becomes deposited upon the more positive metal. The stain, however, produces an effect of contrast which, when artistically applied, is exceedingly pleasing to the eye ; and by this means ornamental brass and also electro - brass work is greatly enriched by art- metal workers and others to meet the requirements of the public. Since it is important that electro -depositors of brass should be well acquainted with the methods of producing upon their work the varied effects which are applied to the solid alloy, we will now explain some of the many processes adopted. Black Bronze. This is produced, as before observed, by means of a dilute solution of chloride of platinum. For this purpose, the platinum salt may be dissolved in spirits of wine,^ methylated spirit, or distilled water, and a few drops of the concentrated solution added to a small quantity of water, and applied with a camel-hair, brush or by dipping. For large pieces of work, a sufficient quantity of the dilute solution should be prepared to finish the piece in hand, so as to ensure uni- formity of tone throughout the entire piece. When bronzing very large articles, as stove fronts, fenders, &c., it is sometimes the prac- tice to mix a little of the dilute platinum solution with plumbago, made into a thin paste with water, and to brush this over the entire ornamental surface of the article, and when nearly dry, the article ia well brushed with a rather soft, long-haired brush until quite BRONZING ELECTRO-BRASSED WORK. 385 bright; the high lights, or prominent points of the article, are then gently rubbed with a piece of chamois leather moistened with spirit of wine or rubbed on a lump of chalk, the object being to remove the black stain from these points, so as to show the yellow metal with which the work is coated. Instead of employing the platinum solution for this purpose, a small quantity of sulphide of ammonium may be mixed with the plumbago paste ; this latter is most frequently adopted for the sake of economy. The platinum salt, however, produces the most brilliant and lasting effect. Warm Bronze Colour. When it is desired to give a warm chocolate tone to an electro -brassed article, a mixture of jewellers' rouge and black-lead, in varying proportions according to the tone required, is first made with water ; to this a few drops of chloride of platinum solution or sulphide of ammonium are added and intimately mixed. This bronzing paste is spread over the article with a soft brush, and allowed to become nearly dry, as before, when the surplus powder is brushed away by polishing with a long-haired brush. The high lights are then touched up as before to expose the metal. The article should now be made moderately warm, and then brushed over quickly with a very thin, hard, and quick-drying varnish ; when this is done the work is complete. A bronzing composition for imparting a warm chocolate tone to electro -brassed work may be made by mixing into a paste with water the following ingredients : black-lead, I ounce ; Sienna powder, 2 ounces ; rouge, ounce. To this may be added a few drops of sulphide of ammonium. Or a mixture of black-lead and rouge or crocus may be employed. In each of these cases the formulae may be varied at the will of the operator ; indeed, the tone or bronze effect is so greatly a matter of taste that the proportions of the various materials may properly be left to the discretion of the electro - bronzer. Green Bronze. Mix into a paste with water the following sub- stances, varying the proportions, as before suggested, according to taste : Chromate of lead (chrome yellow) . . 2 ounces Prussian blue . >'-. . . 2 Plumbago ,.,,.. . . . J pound Sienna powder J Lac carmine . ... . . . i When applying the above composition, a small quantity of sulphide of ammonium or chloride of platinum solution may be added. It should be mentioned that the particles set free by brushing off the superfluous portions of the above mixture would be unwholesome to breathe, on account of the chromate of lead present in the composition t cc 386 ELECTRO-DEPOSITION OF ALLOYS. the other substances are virtually innocuous, though the inhalation of small particles of mineral, or indeed any other substance whatever, should be avoided as much as possible. In polishing- work which has been coated with bronzing- powders, therefore, it would be well if the workpeople could be induced to protect the nose and mouth by a thin piece of muslin, more especially in the earlier stages of the polishing operation, when the great bulk of the superfluous material has to be brushed away. French method of Bronzing Electro-brassed Zinc Work. If a warm tone is desired, the electro-brassed article is first dipped in a weak solution of sulphate of copper and then dried. It is next moistened with sulphide of ammonia or a solution of liver of sulphur ; after again drying the surface is brushed over with a mixture of hematite or jewellers' rouge and black-lead, the mixture being made according to the tone required. The brush should be slightly moistened with turpentine to assist the adhesion of the powder. The parts in relief are then to be " set off," that is, well rubbed, to disclose the metal, and give it the appearance of having been subjected to wear. The object is then to be coated with a thin colourless varnish. Green or Antique Bronze. Dissolve in 100 parts of acetic acid of moderate strength, or in 200 parts of good vinegar, 30 parts of car- bonate of ammonia or sal-ammoniac, and 10 parts each of common salt, cream of tartar, and acetate of copper, and add a little water ; mix well, and smear the object with it, and then allow it to dry, at the ordinary temperature, from twenty-four to forty-eig'ht hours. At the end of that time the article will be found to be entirely covered with verdigris, which presents various tints. It is then to be brushed, but more especially the prominent parts, with a waxed brush, that is, a brush passed over a lump of yellow beeswax. The relief parts may then be "set off" with hematite, chrome yellow, or other suitable colours. Light touches with ammonia impart a blue shade to the green parts, and carbonate of ammonia deepens the colour of the parts to which it is applied. Steel Bronze. This is obtained by moistening the articles with a dilute solution of chloride of platinum, and slightly heating them. Since this bronze is liable to scale off with friction, it should not be applied in successive doses, but the solution used should be of such a strength that the desired effect may be obtained, if possible, by a single application. Copper bronze, that is, electro-brass with an excess of copper, may be darkened by dipping it into a weak and warm solution of chloride of antimony (butter of antimony) in hydro- chloric acid. Sometimes, however, the coloration will be violet instead of black. Bronze Powders, as the Bessemer bronzes, -for instance, are largely LACQUERING ELECTRO-BRASSED WORK. 387 used for imparting a metallic appearance to plaster casts and ceramic wares, and also for ornamenting cast-iron work, to give it the ap- pearance of bronze. The mode of application is as follows : The article, after being cleaned, is coated with a fatty drying varnish, which is allowed to become nearly dry. The bronze powder is then applied with a badger -hair brush, when it firmly adheres to the sticky varnish. After drying, the article is coated with a hard, colourless varnish, which fills up the details. This process is chiefly applied to metals for such work as cheap iron fenders, cast-iron dogs for fireplaces, umbrella- stands, and other coarse work, and is in no degree suitable for articles which have been electro -brassed, in which a more artistic finish is required. Dipping Electro-brassed "Work. When steel or iron articles have received a good coating of brass, but of an indifferent colour, they may be greatly improved in colour by being dipped in the ordinary dipping liquids used for brass. The dippings, however, must be done with great promptitude, otherwise the coating will either be dissolved off, or at least much reduced in thickness. If the operation is conducted with smartness, and the articles at once plunged into cold water, the desired result may be obtained without risk provided, of course, that a tolerably stout coating has been deposited upon the work. This method of improving the colour of the deposit we have successfully adopted, and, indeed, frequently made it a practice to give to the work an extra strong coating to allow for the reduction of its thickness in the acid dip. By this means we were enabled to produce results in electro -brassing which were acknowledged to be fully equal in colour to the finest specimens of solid brass, and not unfrequently superior. Lacquering Electro-brassed Work. After being worked for some time, a brassing bath is liable to give deposits which are either too red, or coppery, or they may assume a sickly pale colour, which, after scratch-brushing, is of too light a colour to fairly represent brass. Articles in this condition, although they may be greatly improved by a coating of good yellow lacquer, still fail to resemble ordinary brass. "When zinc or steel articles are required to be lacquered after electro - brassing, it is a good plan to be provided with an extra brassing solu- tion, capable of yielding a really good colour, in. which the articles, after being coated in the ordinary bath and scratch-brushed, may be immersed, to give them a final coating of good yellow brass. Generally speaking, an immersion in the second bath of only a few minutes is sufficient to produce the desired effect, and the solution we should recommend for this purpose is one prepared from the sulphates of copper and zinc, precipitated by carbonate of potash, and redissolved with cyanide and liquid ammonia. A solution carefully prepared from these ingredients is capable of yielding a brass deposit of a very 388 ELECTRO-DEPOSITION OF ALLOYS. fine colour. The solution should be used only for giving a final coat- ing to electro -brassed work which is of a bad colour, and when it ceases to yield a good coloured deposit, it may be added to the ordinary brassing bath and another solution prepared in its place. If the plan we have suggested be adopted, the work may then be lacquered in the same way as ordinary brass, after being thoroughly rinsed and dried. It may be mentioned that acid dipping, to improve the colour of the brass deposit, cannot so safely be applied to zinc work which has been electro-brassed. Electro -deposition of Bronze. The electro -deposition of the alloy of copper and tin known as bronze is less frequently practised than that of the more common alloy, brass ; indeed, the latter with an excess of copper in the solution generally answers the purpose equally well for most of the uses to which the deposited bronze alloy would be applicable as an imitation of real bronze. In making up a bronz- ing solution, it is only necessary to substitute a salt of tin (chloride of tin by preference) for the zinc salt in the preceding formulae, but in rather less proportion than the latter, say about one-third less. The simpler method, however, is to make up a brassing bath with a slight excess of copper, and to depend upon the artificial methods of bronzing previously given, or such modifications of them as may suggest them- selves, for producing imitations of solid bronze. A very little practice in this direction will enable the operator to meet almost every require- ment as to tone or colour. In this, as in the case of electro -brassed work, the most prominent parts of the work should be rendered bright, so as to expose the deposited metal at such points by gently rubbing away the materials used in producing the artificial bronze colour. By so doing a very pleasing artistic effect may be produced, provided the removal of the bronzing material is not carried too far, but merely confined to such points as may be assumed to have been subjected to friction in use. Electro -deposition of German Silver. We have succeeded in depositing an alloy of copper, nickel, and zinc, forming German silver of good quality, by making a solution of the alloy in the direct way, as recommended for preparing brassing solutions, thus : Cut up into small pieces sheet German silver, about one ounce ; 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 the 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 three pints of cold water in a gallon vessel. Next dis- DEPOSITION OF AN ALLOY OF TIN AND SILVER. 389 solve about four ounces of carbonate 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 solution of cyanide with stirring, and about one ounce of liquid ammonia. 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 then 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 twelve 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. Morris and Johnson's Process. By this process a German silver bath is prepared by the battery method. One pound each of cyanide of potassium and carbonate of ammonia are dissolved in a gallon of water, and the solution heated to 150 Fahr. A large German silver anode, connected with the positive electrode of a powerful battery, is immersed in the solution ; a small cathode of any suitable metal is connected to the negative pole of the battery and also immersed in the solution. The electrolytic action is to be kept up until a considerable amount of metal is dissolved, and a bright cathode receives a deposit of good colour, when the solution is ready for use. If the deposit is too red, carbonate of ammonia is to be added ; if too white, cyanide of potassium. The electro -deposition of German silver may with advantage be substituted for nickel-plating for many articles of ornament and use- fulness ; a coating of this alloy looks exceedingly well upon bright steel surfaces, and is, to our mind, specially suitable for revolvers, dental instruments, and scabbards, having, when deposited of a good colour, a more pleasing tone than that of nickel. Deposition of an Alloy of Tin and Silver. Messrs. Round and Son obtained a patent in 1879 for a process for depositing an alloy of tin and silver, which is said to be applicable to coating brass, German silver, and copper, and, if slightly covered with a film of copper, iron and steel also. The inventors state that from their solution a white reguline metal is obtained which is easily polished, and greatly re- sembles fine silver. The solution is prepared as follows : Dissolve 80 ounces of commercial cyanide of potassium in 20 gallons of water in a suitable vessel ; then pour in 100 ounces by measure of strong 3QO ELECTRO-DEPOSITION OF ALLOYS. liquid ammovaa, of the specific gravity of 880, stirring well together ; next add 10 ounces of nitrate of silver ; any soluble tin salt may then be added at discretion ; now add 3 pounds of carbonate of potassa, and allow the compound solution to rest until all sediment has sub- sided, then carefully decant the clear liquor, and the bath is ready for use. It is worked with a large anode of tin and a smaller one of silver. The articles to be plated by this process are cleaned in caustic ley, and all oxide carefully removed ; they are then immersed in the bath, in connection with the negative pole of a strong voltaic battery, the two anodes being connected to the positive as usual. The articles are allowed to remain in the bath until the required thickness of deposit is obtained, when they are removed, rinsed, and dried, and may then be polished or burnished to a high degree, closely resembling un- alloyed silver, but produced at far less cost. Deposition of Alloys of Gold, Silver, &c. These are noticed in Chapter XV. on Electro -gilding. We may, however, state that by mixing gold and silver cyanide solutions in varying proportions, gild- ing of various shades of colour may be obtained. The same results may be effected by blending cyanide solutions of gold and copper. The colour of the deposit is greatly influenced by the strength of the current employed, the amount of anode surface, and the temperature of the bath. "With these hints to guide him, the experimentalist may obtain very interesting results by modifying the condition of the bath, strength of current, &c., at will. Deposition of Chromium Alloys. Slater's Process. This pro- cess, for which a patent was obtained in March, 1884, may be thus briefly described : Anodes of chromium alloy are prepared by heating chromium compounds with charcoal in a closed crucible, and pouring upon the reduced mass 2\ parts of fused copper, and, subsequently, from I to I \ parts of molten tin, and then granulating, re-fusing, and casting in moulds of the desired form. The plates thus formed are used as anodes in a solution made by dissolving I pound of cyanide of potassium and one pound of carbonate of ammonia in a gallon of water, heated to 150 Eahr., until a good deposit of alloy is formed upon the cathode ; the bath is then ready for use. To finish the articles coated in this solution, they are " coloured " in a bath com- posed of chloride of tin 6 to 8 parts ; chloride of copper, 20 to 25 parts ; bichromate of ammonia, 10 to 15 parts , chloride of platinum, 6 to 12 parts, and water 101 to no parts. A very moderate current only is required. Deposition of Magnesium and its Alloys. Gerhard and Smith obtained a patent in December, 1884, for the following process: Ammonio -sulphate of magnesia is prepared by dissolving and crystal- lising together 228 parts of sulphate of magnesia (Epsom salt), and NEW WHITE ALLOYS. 39! 132 parts of sulphate of ammonia. The crystals are dissolved in 35,000 parts of water, and the solution thus formed is best used at a temperature of 150 to 212 Fahr. For white metal, a nickel anode is used ; for magnesium bronze, a copper anode must be employed. In the latter case, the bath is formed of ammonio- sulphate of magnesia, 360 parts ; cyanide of potassium, 550 parts, and carbonate of ammonia, 550 parts, dissolved in 35, coo parts of water. .Alloy of Platinum and Silver. Mr. Milton H. Campbell, of America, has taken out a patent for depositing this alloy, which is said to resist the action of nitric acid and sulphides. A bath is made by dissolving 30 parts of platinum and 70 parts of silver in aqua regia, and the metals are precipitated as a grey powder by means of chloride of ammonium. The compound chloride thus obtained is dissolved in a solution of cyanide of potassium, which constitutes the electrolytic bath. The anode is an alloy of 3 parts of platinum and 70 parts of silver, a feeble current being employed for the deposition of the alloy. New White Alloys. Many attempts have been made by refiners and metal workers to produce a metallic alloy to resemble silver in whiteness and texture, and sufficiently low in price for general manu- facturing purposes ; but although many excellent results have been obtained, there is no doubt whatever that the new alloy introduced by Messrs. Henry Wiggin and Co., under the title of " Silveroid," is the nearest approach to silver yet produced. This pretty alloy is not only beautifully white and of close and fine grain, but has a silvery lustre which renders its commercial name exceedingly appropriate. The new alloy, moreover, files and turns well, and is susceptible of a high polish. Being readily fusible, it is admirably adapted for ornamental castings, and produces very fine work. It is, we understand, being adopted for carriage, railway, and steamship fittings, machinery- bearings, taps, &c., and is intended as a substitute for brass, bronze, and gun-metal in all cases where a brilliantly white metal would be preferred as a substitute for the commoner alloys. A specimen of rolled " silveroid " sent to us by the above firm many months ago has undergone no change in appearance, being as white and silvery as when first received. Silveroid is an alloy of copper and nickel, to which zinc, tin, or lead in varying proportions are added, according to the purpose for which it is to be used. Another alloy has been introduced by Messrs. Wiggin & Co., under the title of "cobalt bronze," which is more steel -like in colour than the former, and is also much harder. This alloy, which takes a bright polish, is suitable for all kinds of work in which a hard, white, non-tarnishable metal is required, and would, we should say, be invaluable for steamship and railway carriage fittings, and work of that class. The cost of this 392 ELECTRO-DEPOSITION OF ALLOYS. alloy is rather higher than " silveroid," owing to the metal cobalt being one of its necessary constituents. Since it does not much exceed, the price of ordinary German silver, however, while being much whiter, we have no doubt that it will be accepted as a valuable substitute for the former for unplated spoon and fork work. A long exposure of a sample of this alloy to the atmosphere, and also to the mingled fumes of our laboratory, by which it was unaffected, establish the fact that " cobalt bronze " will resist all ordinary atmospheric influences. Notes on Electro-brassing. When the brass anodes become foul r owing to undissolved sub-salts of zinc or copper, or both, forming on the surface, it indicates that the bath requires an addition of cyanide and liquid ammonia. After making these additions, it is well to remove the anodes, rinse them, and scour them perfectly clean. Colour of Bronzes. The tone or colour of the bronzing paste applied to electro -brassed cast-iron work (as fenders, for example) should be regulated according to the colour of the deposit. For instance, for a yellow brass, the black or green tones will be most appropriate, while for deposits of a more coppery hue, the warmer bronzes should be used, as those containing rouge, crocus, &c. Bronze Tone. To deposit metal approaching the tint of real bronze, a slight excess of copper should be added to the ordinary brass- solution. Green Bronze Colour. To impart an artificial green bronze appear- ance to electro -brass, the article may be placed in a closed wooden box, having a saucer containing a little chloride of lime (bleaching powder) placed at the bottom. A small quantity of hydrochloric acid is then to be poured on the powder, the lid of the box immediately closed, and the article allowed to be subjected to the chlorine fumes which are given off, for a short time, after which the article is to be exposed to the air. The process may be repeated until the desired effect is produced. The article should be well coated with brass or bronze before being submitted to the action of the chlorine, otherwise this gas will attack the underlying metal. Fender and Stove Work, which are generally required to be electro - brassed at a very low price, should first be pickled in dilute sulphuric acid for a short time, then rinsed and briskly scoured with coarse sand and water, again rinsed, and placed in the bath. A very strong; current should be employed, so that the article may receive a sufficient coating in a few minutes. After rinsing and drying quickly the bronze paste is applied, and this is to be dried on the article as quickly as possible ; when nearly dry the article is polished, its prominent parts then rubbed up with a piece of chamois leather and dry whiting, and a thin coating of hard spirit varnish laid on while the article ia Trarm ; the object is now finished. NOTES ON ELECTRO-BRASSING. 393 Evolution of Hydrogen during Deposition, A great deal has been written and said concerning the vigorous evolution of hydrogen which commonly occurs with electro -brassing baths when under the influence of the current ; and, while we readily agree with much tkat has been said upon this subject, we must frankly confess that we have generally obtained the best results when the escape of hydrogen has been most brisk. We should certainly not consider a brassing bath, in which deposition takes place directly the articles are immersed in it (the deposit being of a good colour), a defective solution, though evolving hydrogen, since some of our best results have been obtained under such conditions. In depositing very stout coatings of this alloy, how- ever, it is certainly desirable that the evolution of hydrogen should, as far as possible, be prevented, a result which may most readily be obtained with solutions containing a considerable quantity of the metallic constituents. Such baths, however, require a frequent addi- tion of concentrated solution to keep up their metallic strength, which the brass anodes, under the most favourable conditions, fail to do. Keeping up the Strength of the Bath, To keep up the strength of brassing baths, the plan suggested by theauthor in respect of electro - tinning and platinising solutions may be adopted (see page 335). By this method a highly concentrated solution of brass, delivered from a tank above, may be allowed to trickle into the bath while deposition is going on, and thus its metallic strength fairly well kept up. Such an arrangement can be effected with very little trouble, a small barrel, furnished with a tap with a long piece of rubber tubing, being all that is necessary. Solution for Cast-iron Work, $c. The brassing bath for this class of work should be rich in metal, otherwise, even with a strong current, the deposit will take place chiefly, or only, at the corners or prominent portions of the articles. It is better to employ a solution containing a good percentage of metal and small quantity of free cyanide, than a great excess of the latter and a small proportion of copper and zinc. The current for depositing brass upon cast iron, especially in cold solutions, must be strong, and a large anode surface exposed in the bath. The same observations apply, to a certain extent, to lead, which requires a bath rich in copper and zinc to obtain successful results, especially when battery power is employed. Brassing Different Metals, It must be borne in mind, as we have hinted, that all metals do not receive the brass deposit with equal facility ; indeed, if two articles one composed of zinc and the othe? of cast iron were placed in the bath simultaneously the former would at once become coated with brass, while the cast-iron article woul-- either remain uncoated with the alloy, or at most a slight deposit would be visible at the points nearest the anode, or at the lower part? 394 ELECTKO-DEPOSITION OF ALLOYS. of the article, according to its form. This being- the case, the cast- iron article should first be put into the bath, and when this has become perfectly coated all over the zinc articles may then be suspended in the solution. It is better, however, to deposit these metals sepa- rately. Even wrought and cast iron will not receive the brass deposit with equal readiness ; the latter, therefore, should be put into the bath first, and the former only when the cast-iron piece is well coated all over. Brassing in Hot Solutions. When an article is first put into the bath (being connected to the negative electrode) it should be gently moved about for a few moments, to cause the deposit to take place as uniformly as possible all over the surface of the article, and when the characteristic yellow tint of the alloy appears uniformly all over the object, it may be allowed to rest in the bath for a short time, when the slinging wires should be shifted to allow the parts they have covered to become coated with the alloy. After a while the article should be inverted in the bath to equalise the deposit as far as possible. With these exceptions, it is not judicious to disturb work in brassing solutions while in circuit, as the colour of the deposit is often affected even by slight motioa. CHAPTER XXIX. ELECTRO-METALLURGY. Application of the Term. Dechaud and Gaultier's Process. Electrolytic Refining of Copper by Separate Current. Elkington's Process of Re- fining Copper by Electrolysis. Dr. C. W. Siemens' Observations on the Electro-metallurgy of Copper. Mr. B. N. S. Keith on Refining Copper by Electrolysis. M. Thenard's Experiments. Dr. Higgs' Observations. Dr. Kiliani's Observations on the Electrolytic Refining of Copper. Gramme's Experiments with Sulphate of Copper Baths. Application of tlie Term. The term Electro-metallurgy, which, was applied by the late Alfred Sniee to the art of electro -deposition of metals generally, is now more correctly applied to the refining- or purification of metals, and to their separation or extraction from ores by electrolysis. This important branch of electro-chemistry, the practical development of which had long been the dream and the hope of electricians, has during the past twenty years gradually developed into an art of considerable magnitude, while the great improvements in magneto and dynamo -electric machines which have been made within a comparatively recent date have given a stimulus to this field of enterprise which is likely to render it one of the most important in its employment of electric machinery. That these great results could never have been profitably obtained by means of voltaic electricity, is beyond all question. An early investigation of this subject was made by Maximilian, Duke of Leuchtenberg, in the year 1847, who proved that impure copper containing precious metals could be refined so as to yield pure copper, and leave the precious metals in a condensed form ready for further treatment. He moreover recognised the great influence which his discovery would eventually have in connection with practical metallurgy. At this time, it must be remembered, electrolytic operations were, with the exception of Woolrich's magneto -electric machine, wholly conducted by means of the current from voltaic batteries, which rendered the following up of this discovery for com- mercial purposes practically impossible. The introduction of Wilde's magneto -electric machine in 1865 may fairly be taken as the starting- point from which success in this direction became possible as regards 396 ELECTRO-METALLURGY. the means of obtaining electric power. In the same year Mr. J. B. Elkington introduced a practical process for refining copper by electro- lysis, and which, worked by currents from Wilde's successful machines, soon placed the art of refining copper electrolytically upon a sound practical basis. A brief description of this process will be given farther on. There can be no doubt that the first instance of the application of electrolysis in metallurgy was in the production of what is termed "cement" copper in the wet method of treatment. The drainage water of copper mines is frequently charged with sulphate of copper, due to the oxidation of the sulphide contained in the ore, and it is from these cupreous liquors that the cementation copper is obtained. The wet process is particularly adapted to the treatment of the poorer oxidised ores, especially where fuel is scarce. These ores are treated with acid, either hydrochloric or sulphuric, or with a solution of ammonia, all three of which are good solvents of the oxides of copper. The precipitation is effected in the copper solution by placing iron in it. The action is the result of electrolysis ( Williams}* The cupreous solution being placed in large tanks, fragments of iron are immersed and the copper becomes reduced to the metallic state in the form of a spongy deposit to which the term ' l cementation copper ' ' is applied. The first patented improvement on the above method, and which may also be considered the first application of a distinctly electrolytic process to the reduction of copper, was due to MM. Dechaud and Gaultier, of France, the patent, dated 1846, being for " Improve- ments in the extraction of copper from its ores, founded particularly on electro -chemical methods." The process, whieh we abridge from Mr. Williams's able work, is as follows : Dechaud and Gaultier 's Process. The inventors prepare the sulphate of copper from sulphide and oxide ores, by roasting them in a furnace, and then extracting the copper by lixiviation. The pro- cess, which exhibits much originality, is thus described by the inventors : " If a mixture of oxide of copper and of sulphate of iron or zinc is subjected to the action of a suitable temperature, and of an air current, the resulting product will be sulphate of copper and sesquioxide of iron or oxide of zinc." The ore was first roasted and washed before being mixed with the sulphate of iron. The pro- portion of sulphate to ore was determined by previous experiment on a smaller scale. The inventors also found that carbonate ores of copper could be reduced in the same way. The suitable quantity of reducing sulphate having been well mixed with the dried roasted ore, * " Mineral Resources of the United States," by Albert Williams. Govern- ment Printing Office, Washington, 1883. DECHAUD AND GAULTIEE'S PROCESS. 397 the mixture was roasted in a reverberatory furnace ; it was after- wards thoroughly washed to dissolve the sulphate of copper formed. If the assay showed that the residue still contained copper, it was again mixed with sulphate and roasted. Instead of introducing iron into the copper solution in the ordinary way, by which the copper becomes deposited upon this metal and contaminated with impurities from the iron, MM. Dechaud and Gaultier proceeded as follows : The solution was first concentrated by evaporation, and then placed in large shallow wooden tanks lined with lead. On the bottom of each tank were placed a number of flat copper plates, whose under surfaces were insulated with varnish so that the deposit could take place on the upper sides only. At the upper part of the solution, plates of iron, cast with grooves and openings like a gridiron, so as to present more surface and allow the escape of gases, were suspended in the solution of sulphate of copper by means of lugs, which rested on the edges of the tanks. All the copper plates were connected together electrically, as also were the iron plates. On connecting the two sides i.e., the combined copper plates with the combined iron plates a battery arrangement was effected, and the deposition of copper took place upon the cathode surfaces (the copper plates), while the iron plates (acting as anodes) became dissolved into the solution. To prevent the impurities from the iron mixing with the pure deposited copper, the inventors employed a porous diaphragm of cotton cloth between the two sets of plates. Instead of employing copper cathodes, they sometimes used leaden ones, from which the copper was more readily detached. Since during the electrolytic action the solution naturally grew weaker in copper, being replaced by sulphate of iron, these ingenious inventors provided a system of automatic circulation by means of leaden pipes connected with reser- voirs, whose valves were controlled by the rise and fall of hydrometers. One set of pipes delivered fresh copper solution to the bottom of the tank, which of course caused the liquid to rise in the vessel : another pipe placed at the upper part of the tank drew off some of the sulphate of iron, and in this way the solution always maintained the same density, and contained one uniform proportion of copper. The sulphate of iron liquor was afterwards evaporated, and the salt obtained by crystallisation, which could then either be disposed of as copperas, or employed in treating fresh batches of ore. It is stated that about 2,200 Ibs. of copper could be reduced per day by the above process. In a subsequent addition to their patent, MM. Dechaud and Gaultier describe a method of utilising the sulphurous acid gas liberated during the roasting of the ore. Electrolytic Refining of Copper by Separate Current. This method of obtaining pure copper is now most extensively carried on 398 ELECTRO-METALLURGY. in various parts of England, on the Continent, and in America, the amount of pure metal annually produced being enormous. One great advantage of this method of refining is that the crude coppers operated upon frequently contain considerable quantities of gold and silver, which valuable metals become entirely removed from the impure metal, and are readily recovered by ordinary refining processes. Another important feature in this system is that when the process is properly conducted the copper obtained is pure a most important consideration when the metal is required for conducting electricity, as in the case of wire for submarine cables, telegraphs, and the wires employed in the construction of magneto and dynamo -electric ma- chines, and other electrical apparatus. Eespecting the presence of gold in copper refined by the ordinary method, or "dry way," we remember the great public excitement that occurred about the year 1844, when it was discovered that the copper coinage of "William IV. contained a considerable quantity of gold. So soon as the fact became known, many persons of the Hebrew persuasion became large pur- chasers of penny pieces, at prices ranging from three -half pence to twopence each, and many were those who enjoyed the luxury of collecting these coins for the purpose of reaping the advantage of their extra market value. It is well known that by the ordinary refining processes it is practically impossible to extract from copper the gold and silver which not unfrequently exist in this metal in con- siderable quantities. By the electrolytic method, however, not only are these precious metals recovered, as a natural part of the process, but other impurities as bismuth, arsenic, iron, manganese, &c. become separated, and chemically pure copper is obtained, which, from its superior conductivity, realises a higher market value than the best refined copper obtainable in the " dry way." In the following pages we have given the views and experience's of some of the highest authorities upon the subject of electrolytic re- fining, from which not only the student, but the practical operator, will glean much that is instructive and useful in this important branch of electro -deposition. A few observations upon the general principles of electro -metallurgy, as applied to the refining of copper more especially, may, however, prove useful to those who have not as yet studied the subject. In the electrolytic process of refining copper, the electrolyte employed is a nearly saturated solution of sulphate of copper, contained in a series of tanks, which are placed in electrical communication with each other by copper connections, as many as forty baths or even more being electrolysed by the current from a single magneto or dynamo -electric machine, which, however, is usually an exceedingly powerful generator of the current, or more properly .converter of heat into electricity. The wires which form the coils of ELECTEOLYTIC REFINING OF COPPER. 399 the dynamo machines* employed in the electrolytic treatment of copper are usually drawn from the chemically pure copper obtained by the eletrolytic method, and therefore possess the highest conduc- tivity of which this metal is susceptible. In the best constructed machines to be used for depositing copper, the thickness of the coil wires is so regulated that a current of low electric -motive force fre- quently from one to three volts only is obtained, by which the purity of the copper deposit is insured, and the deposition of metallic impu- rities upon the cathode (which require a higher E.M.F.) prevented. In most electrolytic copper refining works the anodes consist of cast slabs or plates of crude copper, containing not more than from 3 to 4 per cent, of impurities. The cathodes are thin sheets of pure copper, present- ing the same surface as the anodes. To diminish the resistance of the bath as much as possible, the anodes and cathodes are arranged as close to each other as practicable without danger of coming in contact. When the current passes through the series of tanks, the sulphate of copper solution becomes decomposed, its copper being gradually deposited upon the cathodes, while the liberated sulphuric acid dissolves an equivalent proportion of copper from the anodes, forming sulphate of copper, by which the strength of the solution is kept uniform that is to say, so far as the impurities of the copper will allow. If pure copper anodes were employed, the solution would keep in a perfectly uniform condi- tion, excepting- as regards loss of water by evaporation ; but with impure anodes the bath gradually becomes charged with iron and some other soluble metallic impurities, which in course of time render the bath too foul, if we may use the term, to be further worked, in which case the solution is removed and replaced by a fresh solution of sul- phate of copper. The depositor " mud " which collects a^t the bottom of the tanks is removed from time to time, and the gold and silver afterwards recovered by the ordinary processes of refining. In arranging an electrolytic copper refining plant, the resistance of the bath is diminished by increasing the anode and cathode surfaces, by which the cost of the electricity and consequently of the motive power is greatly reduced. If, however, this is carried to the fullest extent, it necessarily involves the employment of a costly stock of copper as anodes ; it is therefore preferred by some electro -metallur- gists (especially in districts where coal is cheap, or where water power can be obtained) to increase the expenditure of power rather than absorb interest on capital by increasing the quantity of copper in the baths, which would in many cases absorb a large proportion of the profits. When a quantity of copper is refined with a given power, * In speaking of dynamo-electric machines in connection with this subject, -we wish to be understood as including magneto-electric machines also. 40O ELECTROMETALLURGY. and it is desired to double the production without increasing the ex- penditure of power, it becomes necessary to quadruple the quantity of metal to be treated, which greatly increases the cost of the original establishment . The interest of the capital thus absorbed must therefore greatly reduce the annual profit. One hundred and fifty baths joined in series and worked with two powerful dynamo -electric machines, also joined in series, is considered by some an economical arrangement. The views of electricians, however, differ greatly in this respect, and we believe that the system adopted in this country and that pursued on the Continent are widely different in many essential features. "We have been informed that some Continental machines require 10,000 square feet of copper surface (as anodes) per machine, which neces- sarily involves a very large amount of capital where a large number of machines are employed. "With some of our English machines only 2,000 square feet of copper surface as anodes (or say 10 tons of copper) are required for a plant of the same out-putting capacity, which greatly reduces tha^*pl)pfr of capital required for copper in stock. It must also be l@p&m mind that with the larger anode surface tanks of greater fl^ftcTty are required, and consequently a larger bulk of copper ^Solution, besides a proportionate increase in the cathode sur- face, and in the number of conducting rods. Elkington's Process of Refining Copper by Electrolysis. The impure copper, as it comes from the smelting furnace, is cast into slabs or plates, about 18 inches square and f inch thick, with lugs projecting from their corners at one end. These plates are placed in troughs, each sufficiently long to take two plates, end to end ; three such rows of plates, or six in all, are placed in each trough, a space of about 6 inches being left between the rows. The lugs of the plates rest on the ends of the trough, and upon a cross-bar fixed mid- way of its length, to which part strips of copper are attached, and these are all placed in metallic contact with each other. Cathodes of pure thin sheet copper (about 3\nd of an inch in thickness) are arranged between the rows of slabs or positive plates, the cathodes being about the same size as the cakes required for the market, or about 1 2 by 6 inches. There may be four such plates (cathodes) in each row, or sixteen in each trough. These negative plates are each cut with a projecting tongue, by which they are fixed to a frame made of copper rods, the tongue of each plate being lapped round the frame and thus connected and held. The frame has arms at its four corners, which rest on the sides of the trough, on which are copper strips insulated from the strips at the end of the trough. In this way a series of twenty -five troughs are made, the negative plates of one trough being connected with the positive plates of the next, and so on throughout the vhole series, the positive plates being at one end of the series DR. SIEMENS ON THE ELECTRO-METALLURGY OF COPPER. 40! and the negative at the other. Care is taken that all metallic connec- tions are clean and the contacts perfect. The troughs are charged with a nearly saturated solution of sulphate of copper. The negative and positive plates are then connected to the corresponding poles of a large magneto -electric machine, having, say, fifty permanent magnets weighing 28 Ibs. each, and fully magnetised.* When the positive plates have become so far dissolved and corroded that fragments are likely to fall from them, they are replaced by others, and the old ones recast. The negative plates may be kept in the baths until they are f inch in thickness. The sulphate of copper solutions are kept at work until they be- come so charged with sulphate of iron that their further use is incon- venient, when they are changed, and the copper recovered by the usual means. The residue which accumulates at the bottom of the troughs is removed from time to time, and since it frequently contains a con- siderable percentage of silver, some gold, and also tin and antimony, it has a certain market value, and may be sold to the refiners. Mr. Elkington prefers to work with crude copper known as " blister " or "pimple copper," rather than with that obtained from the earlier stages of the smelting process, which contains higher percentages of impurity. Dr. C. W. Siemens' Observations on the Electro-metallurgy of Copper. In his address to the Society of Telegraph Engineers, in January, 1878, Dr. Siemens said, " The dynamo -electric machine has also been applied with considerable success to metallurgical processes, such as the precipitation of copper, in what is termed the ' wet process of smelting.' The effect of I horse-power expended in driving a dynamo -electric machine of suitable construction is to precipitate 1,120 Ibs. of copper per 24 hours, equivalent to an expen- diture of 72 Ibs. of coal, taking a consumption of 3 Ibs. of coal per horse-power per hour." It is stated that even this startling result has been surpassed, owing in a great measure to the important improvements in dynamo -electric machines which have been effected since the above gratifying statement of the great electrician was made. BSr. B. IT. S. Keith on Refining Copper by Electrolysis. In a very able paper upon this subject, Mr. Keith proposes the fol- lowing experiments to show under what conditions an increase of copper deposit may be obtained from a given value of electric power, and the important results obtained will prove invaluable to students and to those who are engaged in depositing copper either in electro- * The machines referred to have been greatly improved by Mr. Wilde since, as will be noticed on referring to page 26. D D 402 ELECTRO-METALLURGY. typing or in the process of refining by electrolysis. We extract the following from this interesting paper, but refer the reader to the journal in which it appeared * for more elaborate details. Mr. Keith says : "Take a Smee cell, having 5 Volt, electro -motive force, -5 ohm. resistance, and connect with a copper electrolysing .cell having a resistance of -5 ohm. The result will be a current of '5 Veber ; one Veber current causes the solution of 18-0 grains of copper from the anode, and deposition of the same amount of copper per hour upon the cathode of an electrolysing cell. An equivalent quantity of 18-46 grains of zinc is dissolved in the Smee cell. So the amount of copper deposited by this arrangement is 9-0 grains per hour. Next take a DanieU cell, having an E.M.F. of I Volt., resistance of -5 ohm., and connect with the same electrolysing cell. The current will be I Veber. The amount of copper deposited by this arrangement is 18-0 grains per hour, and 18-46 grains of zinc are dissolved in the Daniell cell. Next take a Bunsen cell, having say 2 Volts. E.M.F. and resistance of -5 ohm., con- nect with the electroly- sing cell, and we have a current of 2 Vebers. The copper deposited is now 36 grains per hour, and 36-92 grains of zinc are dis- solved. In these threo cases we observe that in- creased E.M.F. increases the speed of the deposi- tion, i.e. more copper is deposited per hour. We also observe that the relative quantity of zinc dissolved remains the same in the three cases i.e. an equivalent of zinc for an equivalent of copper. We cannot well change the E.M.F. of these cells, but we can their resistance, by making them larger for less resistance, and smaller for more resist- ance. We can in the same way change resistance of electrolysing cells. For less resistance, make the anode and cathode larger. Having made two electrolysing cells, twice as large as the one we have been using, they have each then a resistance of -25 ohm. Connect in succession the several galvanic cells with the electrolysing cells, as by the accompanying diagram, Fig. 121, in which the arrows show the direction of the current." I is the battery cell, z and s signifying the zinc and silver elements, 2 and 3 are electrolysing cells, A c repre- senting the anodes and cathodes respectively. Fig. 121. Engineering and Mining Journal, New York. KEITH ON EEFINING COPPER BY ELECTROLYSIS. 403 By the above arrangement the E.M.F's., the resistance, and the current are the same, and the same amount of copper deposited in each of the electrolysing cells, or twice as much in the aggregate as before, while no more zinc is consumed. It is the same when 3,4, 10, or more electrolysing cells are used, their size being increased 3, 4,10 times, as the case may be, so as to preserve the same resistance, and it is found that 3, 4, 10, &c., times as much copper is deposited, with no increase in the consumption of the zinc. It will be observed that the speed of the deposit with the Daniell cell series was twice as much as in the case of the Smee, and with the Bunsen four times as much as the latter. " This relation continues throughout," says Mr. Keith, "as the character of the deposit changes with increased cathode surface, the tendency being to form crystals of metallic copper, not coherent ; the practical limit of number of electrolysing cells is sooner reached with the battery of lowest E.M.F." Mr. Keith gives the following table of his experiments : i. Galvanic Cell. Smee Taniell Bunsen I'O I'O I'O I'O 2'0 2'0 2'0 2'0 *5 0-5 0'50 0-25 0-166 0'125 0-05 0-50 0-25 0-125 0-05 0-50 0-25 0-125 0*05 I'OO I '00 I'OO I 'CO I -00 I'OO I'OO I'OO I'OO I '00 I -00 I'OO I '00 9-23 18-46 18-46 18-46 18-46 36-92 36-92 36-92 36-92 9'oi 9-01 9-01 9'oi 9'oi 18-03 1 8 '03 18-03 18-03 36-06 36-06 36-06 36-06 9'oi 18-03 27-04 36-06 90-15 18-03 36-06 72-12 180-30 36-06 72*12 144-24 36o'6o o'5 I'O I'O I'O ro 2'0 2'0 2'0 2'0 The foregoing figures are not given as exact, but near enough to illustrate the principles involved.. Refining Copper by Dynamo-electricity. The dynamo -electric ma- chines employed in refining copper by electrolysis are constructed to yield currents of low E.M.F., because the soluble anodes, being of 404 ELECTRO-METALLURGY. the same material as that deposited upon the cathode, no force is absorbed during the solution and reduction of the metal. Dynamo machines of high E.M.F. and low resistance require smaller anode and cathode surface in the electrolytic bath for a given amount of copper deposited, while those of low E.M.F. and low resistance, yielding currents of great quantity, require much larger anode and cathode surfaces for the same amount of copper deposited. The latter type of machine is less costly than the former. Copper, regulus, blue metal, black metal, &c., vary in their consti- tution from say 74 to 98 per cent, of copper, with varying propor- tions of sulphur and iron as the chief impurities. The impure metal is made the anode in a bath of sulphate of copper, and sheet copper is employed as the cathode. During the electrolysis copper and iron are dissolved, and copper is deposited on the cathodes at the same rate as. it is dissolved. Sulphur will remain undissolved, and will rise to the surface of the solution in flocculent masses, which may be collected. Iron and zinc remain in the solution, and lead falls down as sulphate of lead. If gold and silver be present, the former will fall to the bottom as a metallic powder, and if small quantities of chlorides (as common salt, for instance) are added to the solution, the latter will also fall to the bottom in the form of chloride of silver. The insoluble residues may be collected, and the precious metals recovered by the usual processes. "When the solution becomes surcharged with iron, zinc, &c., a portion of the solution is removed from time to time and replaced by water and sulphuric acid, by which means it may be kept in working condition for an indefinite period. The sulphuric acid is added to dissolve the iron, zinc, &c., and no more than is necessary for this purpose need be employed. The purer the copper under treat- ment, the less acid will be required, and also smaller proportions of the solution will require to be removed. (Keith). The economy of the operation, says the same author, "consists in using a proper dynamo -electric machine, with large vats, large surfaces of the impure metal, large surfaces of copper to receive the deposits composing each electrolysing cell, and many of the cells placed in series."' M. Thenard's Experiments.* This famous chemist made some investigations concerning the advantages of the compound bath in electrolysis, the source of the current being a Gramme magneto - electric machine, having a permanent Jamin magnet, and driven by a Lenoir engine. The liquid used was composed of 125 parts of sul- phate of copper, the same amount of sulphuric acid, and 1,000 parts of water. The number of revolutions was from 1,200 to 1,300 per minute ; the electrodes immersed in each bath were three plates of * Scientific American Supplement, 1877. THENAED'S EXPERIMENTS. 405 64-7 inches in area, each placed parallel and facing each other. The outer plates of each group, distant from the middle one 0-78 inch, -worked positively, the inner plate negatively, so that the latter, on its two faces, became charged with the copper from its neighbours. Six- teen baths were so arranged, and the current established. At the end of one hour the exact weights of the middle cathodes were determined, there being upon each a regular [reguline ?] and strongly adherent deposit. Then, at intervals of twenty minutes thereafter, one bath was removed, so that the current might first pass through sixteen, then fifteen, and so on, until all the baths had been taken out of action. The middle cathode of each bath in turn, on stoppage, was removed, washed, dried, and accurately weighed. The following table exhibits in grains the result of the investigation : No. of Baths. Period of im- mersion. Augmentation of weight of each cathode. Gain per cathode per twenty minutes. Total weight of copper deposited in twenty minutes. h. m. 16 20 I'2IO 210 19-360 15 o 40 2-445 '222 18-330 14 I OO 3725 .241 I7'374 13 I 20 5*085 271 16-523 12 I 40 6-495 299 I5-588 II 2 CO 7'995 332 14-652 10 2 20 9-535 362 13-620 9 2 40 "-I55 '394 12-546 8 3 oo 12-775 419 II-352 7 3 20 I4-535 '453 10-171 6 3 40 16-270 480 8-880 5 4 oo 18-040 500 7-500 4 4 20 19-990 540 6- 1 60 3 4 40 22-000 570 4-710 2 5 oo 24-140 '610 3-280 I 5 20 26-290 1-640 1-640 It will be seen from this that the quantity of copper deposited in a given time augments with the number of baths, although the cathodes of each one of the latter is charged with a less amount of metal. The mechanical effort, on the other hand, was found to increase very sensibly with the diminution in the number of baths. These experi- ments were many times repeated with uniform results. The electrodes were then connected for quantity, instead of for tension, and it was found that the sum of all the deposits was constant, regardless of the number of electrodes. The quality of the deposit was moreover improved in proportion to the augmentation of the latter. These results "demonstrate," Mr. Keith observes, "that less power 406 ELECTRO-METALLURGY. (in proportion of I-2IO to 1-640) was required to produce a deposit of 19-360 in 16 vats in 20 minutes than to deposit 1-640 in a single vat in the same time, thus saving about 94 per cent, of the power. If the size of the electrodes had been increased, so as to keep the total resist- ances the same, the result would have been 1-640 X 16 = 26-240 for the same power used. If the vats had been increased in number to thirty-two, without increasing their size, the power used would have been about one-half what was used with one, and the total deposit about 26-200. If they had been increased in size as well as number to thirty-two, so as to have the total resistances the same, the result would have been 52-480 for the sajne amount of power expended on one, a saving of 97 per cent, in power." It will thus be seen that the economy of the electrolytic process of refining crude copper depends upon the employment of a large number of depositing vats, large anode and cathode surfaces in each vat, and an uniform electrolyte ; the amount of deposit per hour, or per day, will, however, depend greatly upon the percentage of impurities in the crude copper anodes. The system adopted at different refineries varies considerably, as also do the machines employed for producing the current; for example, "Wilde's improved 32 -magnet machine (Fig. 26) requires a series of 130 vats, each having 40 square feet of anode and cathode surface respectively, with which arrangement an aggregate weight of upwards of 900 Ibs. of copper will be deposited in twenty-four hours, with an expenditure of 12 horse-power. With a Siemens 12 machine only 40 baths are required, and several other machines are worked with the same number of baths. At the North G-erman works at Hamburg one installation consists of 40 baths, while in two other series 120 baths are employed. Dr. Higgs's Observations. At a meeting of the Institute of Civil Engineers in 1878, Dr. Higgs made the following statement upon this subject : "For the deposition of large quantities of metal, where, by arranging baths in succession, little change was made in the total circuit-resistance, the dynamo -electric machines gave much greater economy. "With one of these machines and a proper succession of vats, as much as 3 tons of copper have been deposited daily. It is to be observed that the amount of power applied is not stated. I am informed that 1,500 depositing cells are in use. One set of 327 are placed 109 in series, and three in 'multiple arc.' It is without question the cheapest mode of solution of metals, and so little acid is used. In fact, none is necessary after the first solution is made, unless the impure metal contains iron, zinc, &c., which it may not be desirable to save ; then only enough acid to dissolve them is necessary." Dx. Kiliani's Observations on Electrolytic Refining of Cop- per. Dr. Martin Kiliani, of Munich, recently published a long paper DH. KILIANI ON THE ELECTROLYTIC REFINING OF COPPER. 407 in the German Berg-und Hiittenmannische Zeitung, which in an abridged form is reproduced in Engineering * from which journal we will make the following extracts. Referring to Elkington's process before described, Dr. Kiliani observes, " But however simple this process seems in outline, there are many points which would bring great difficulties to an inexperienced person attempting the use of it, if he desired to get, not only silver and gold, but also a good quality of copper. These points depend on the presence of such impurities as arsenic, antimony, bismuth, &c., and on the necessity of carefully observing certain conditions as to strength of current, composition, and circulation of the solution, &c. Elkington, in his patents, does not deal with those points, and this is perhaps the reason, together with the lack of suitable dynamo machines, why the electro -metallurgy of copper did not make much progress beyond Elkington's works till within the last few years. It is really only during the last decade [more particularly within the past three or four years] that the immense progress of electro -technics has extended also to metallurgy, and enabled great successes to be realised in the working of copper, and opened up the prospect of equal successes in other directions." As to the nature of the process itself, Dr. Kiliani begins by saying that the basis of the whole matter consists in the simple fact that when an alloy of several metals forms the anode in the bath, the electric current does not cause the solution of all the component metals at the same time, but that it makes a selection, and takes one metal after the other in a certain order ; and similarly, when several metals are in solution in a bath, the current selects them in a certain order for deposition on the cathode. A fully satisfactory scientific explanation of these facts cannot be attempted, because the whole matter is even yet too little studied, and the materials for a full explanation have not yet been collected. Even as concerns the order of this solution and deposition there are only full materials published concerning silver, copper, iron, zinc, and lead, and then only so far as concerns some few electrolytes. About those elements which are specially troublesome and important in the metallurgy of copper, arsenic, antimony, bismuth, &c., the published information is very superficial and scanty, and in some instances quite incorrect. With regard to the selection of the different metals by the current, Dr. Kiliani says that this ' ' takes place, in general, on the principle that as much energy as possible is created (erzeugt] and as little energy as possible is consumed ; " that is to say, under conditions that metal will be first dissolved from the anode, the solution of which causes the development of the greatest amount of energy (electro - * Engineering, July 3, 1885. 408 ELECTKO-METALLURGY. motive force) ; and that the metal will be first deposited from tha solution on to the cathode, the separation of which requires the least consumption of this same energy. A comparative measure of the energy required in these cases is obtained by taking the heat of com- bination of the metals with oxygen to form oxides or salts. The combination heat of the metals with oxygen to form oxides is taken by the author to form a tabular list in the order in which they are dissolved, as follows : Manganese, zinc, iron, tin, cadmium, cobalt, nickel, lead, arsenic, bismuth, antimony, copper, silver, gold. Of this list it may be said that all those metals which precede copper, when they are present in the anode metals (not oxides) together with copper, will be attacked by the current before the copper ; whereas silver and gold will only be dissolved after the copper, or if they are present in very small amount, they will fall from the anode as powder, and be found in the " mud" of the bath. In practice this order is fully maintained, and all the above metals dissolve before the copper, and are found in solution in the electrolyte, unless they form in- soluble compounds, for example, with lead, when the bath is a sul- phate, as in refining copper. When the metals are once in solution, their deposition on the cathode takes place in the reverse order, beginning with gold and ending with manganese. But the correct- ness of these rules is dependent upon several conditions which must be observed in order that the work may go on in a normal manner. The chief of these conditions concerns the strength of the current, the nature of the electrolyte, the proportions of the metals alloyed together in the anode, and the physical condition of the anode itself. If the current exceeds a certain strength, all the metals may be dissolved and deposited together. The more neutral the electrolyte is, the more easily will the more electro -negative metals be dissolved, and the more easily will the electro -positive metals be deposited. The same may be said of the electrolyte, the poorer it is in copper solution. If the anode consists of copper containing a large amount of impurities, these will be dissolved more easily than from a copper containing but little impurity. The less dense and compact the anode is, the better the process will go on. This all applies only to copper containing the other metals in the metallic form. If oxides or sulphides are present, the first question is as to their conductivity for the current. Most oxides may be classed as non-conductors under the conditions of the bath, and have nothing to do with the action of the current ; they simply go into the insoluble mud, or are dissolved by the purely chemical action of the electrolyte. The sulphides are mostly good conductors, but not nearly so good as metallic co-nper. If, therefore, but a small amount of sulphides is contained in the copper anode, the current will act only on the copper DE. KILIANl's OBSERVATIONS. 409 and the sulphides will be found in the mud unacted upon, unless by the acid of the bath ; if much sulphide is contained in the copper, the current will be more or less divided between the copper and sulphide, and a portion of the latter will be decomposed, with separation of sulphur. In addition to the above secondary reactions of the bath, there are others, some of which are good and some bad, for conduct- ing 1 the process. The current is always striving to decompose the electrolyte into metal (or oxide) and acid ; whilst the liberated acid is striving to redissolve the deposited metal or oxide. These two forces are always opposed to one another, and under varying conditions either may gain the upper hand. The resolvent action of the acid, in cases where the components of the electrolyte have a strong chemical affinity, may overpower the action of a weak current. In the case of copper this secondary reaction is not of much import- ance, copper not being acted upon by dilute sulphuric acid in the absence of air, but still it is quite noticeable in presence of good circulation of the liquor, and more or less access of air in the cathodes. A favourable effect of this secondary action is that any cupreous oxide which may be deposited at the cathode with the copper owing to weakness of current, is dissolved again. Respecting the presence of foreign metals and oxides in the anodes, Dr. Kiliani says, ' ' Cupreous oxide, being a bad conductor, is not affected by the current and goes first of all to the mud of the bath. It is then, however, dissolved by the free acid, more or less, according to the time the acid is allowed to remain in the tank. Therefore any cupreous oxide contained in the anodes diminishes the free acid of the electrolyte, and increases the amount of copper in solution." As to sulphide of copper, if it does not exceed in quantity that usually present in " black copper," it deposits in the mud. If there be a high percentage of copper sulphide in the anode, it is decomposed with liberation of sulphur. Gold, silver, and platinum all remam undis- solved in the mud when they are not present in considerable quantity, and so long as the electrolyte retains its normal composition as to free acid and dissolved copper. If the liquor becomes neutral the silver dissolves and becomes deposited on the cathode. Bismuth and its oxide go partly to the mud, as insoluble basic salt, and partly into solution, eventually precipitating as basic salt. The presence of metallic bismuth in the anode causes the liquor to become poorer in copper, while the presence of its oxide causes a reduction in the amount of free acid. Bismuth does not become deposited upon the cathode, even when large quantities of the basic salt accumulate in the mud, provided the bath be kept in its normal condition as to copper and acid. Tin dissolves in the bath and after awhile is partly deposited again as basic salt. If the anode contains very much tin, the greater 4 1 ELECTRO-METALLURGY. portion remains as basic sulphate, adhering to the anode itself in the form of a deposit of a dirty grey colour while moist, but becoming white when air-dried, increasing rapidly in weight even after long drying at 212 Fahr. ; it contains sulphuric acid, and the tin oxide in it is mostly of the variety soluble in hydrochloric acid. The presence of tin, therefore, reduces the amount of copper in the bath without re- placing it by any appreciable amount of tin in solution. The tin in solution exercises a surprisingly favourable influence on the copper deposit on the cathode. Copper deposited from a neutral solution of pure copper is rough, irregular, and brittle, but if tin be present the deposits are excellent and tough, even though the deposits give no trace of tin. The resistance of the bath is also much reduced by the presence of tin in the anodes. If arsenic be present in the metallic state, it enters the solution as arsenious acid, and only appears in the mud when the solution is saturated with it. Arsenic in the form of arsenic acid combined with oxide of copper, or other oxides, is at once deposited as mud in neutral solutions, since these oxide combinations are non-conductors. Metallic arsenic thus reduces the amount of copper, and increases that of the free acid in the bath, because it goes into the solution without combining with an equivalent of acid, while at the same time a proportionate amount of copper is deposited with liberation of acid. Arsenic does not enter into the copper deposit in the cathode while the bath remains normal as to copper and free acid ; in a neutral bath, or one in which the copper is insufficient, arsenic is deposited with the copper. In reference to the above experiments, it must be borne in mind that they were conducted only upon a laboratory scale, at the Technical High School at Munich, and, therefore, should not be accepted as ruling operations conducted on a large commercial scale. "We may assume, moreover, without questioning their value as facts, that the results were obtained by means of voltaic batteries, and these we know are not so reliable as dynamo or magneto -electric machines properly constructed to yield large currents of low electro -motive force, suitable for the deposition of copper. In the electrolytic treatment of copper, it is undoubtedly of the greatest importance that not a trace of arsenic, bismuth, or any foreign metal should be present in the deposited copper, since it is well known that even one-fifth per cent, of iron depreciates the conductivity of copper by 25 per cent., while a mere trace of arsenic reduces its conductivity by 66 per cent. The uniform character of the deposit and its absolute purity will depend upon the keen observation of the electro -metallurgist, who, while taking care that the machines he employs yield the exact quality of current necessary for the reduction of copper, will also devote special attention to the condition of his electrolytes, and the removal of the GRAMME S EXPERIMENTS. 411 mud so soon as its accumulation in the baths involves risk of partial re -solution. As far as the nature of the current is concerned, it will be seen, by the foregoing remarks, that the requirements of electrolytic copper refiners have been fully met by those of our elec- trical engineers who have paid special attention to this subject. There has been much said about the " secrecy" observed at some of the British and Continental works in respect of their electrolytic opera- tions ; it must be borne in mind, however, that although the principles of the electrolytic art are common property, practice may rary considerably, and special advantages may arise from the sugges- tiveness or keenness of observation of an expert in one establishment, which, if known to competitors, would reduce their value. These tech- nical advantages often represent extra profit. We need say no more. Gramme's Experiments with Sulphate cf Copper Baths. "With a view to determine the proper conditions under which electro- lytic copper refining should be conducted upon economical principles, M. Gramme carried out a series of important experiments, the results of which he communicated to the Academy of Science, in August, 1877, from an abstract of which, by M. Fontaine, we take the fol- lowing (see; pp. 412, 413) : first Series of Experiments. These experiments were conducted with a continuous -current dynamo -electric machine, with a varying number of baths, all placed parallel, and the results showed that, with one or thirty -six baths the deposition is the same with a constant intensity, which confirmed Faraday's law upon a commercial scale. Each bath contained one anode and one cathode only, each having a surface of 16 square decimetres. The intensity [strength?] of the current was 6-3 amperes,. With one single bath the deposit was found to be at the rate of 7 grammes per hour ; with 12 baths it was 7*1 grammes, and with 36 baths (that is with a surface of anodes equal to 6 square metres) it was 7'i grammes, about 2 decigrammes per bath. Second Series. Table I gives the results of experiments conducted with baths connected in a chain, as in arranging a voltaic battery for tension ; the number of these baths varied from one to forty-eight, each having electrodes of the same surface namely, 16 square deci- metres. The speed of the machine was increased as the number of the baths grew larger, and the electro -motive force varied from I to 8 volts. The figures of the tables show that the deposition of copper increased with the number of baths, not only in absolute quantity, but also in a ratio to the work expended in the operation. The weight of copper per kilogrammetre varied from 1-58 gramme up to 33-18 grammes, and even up to 140 grammes, if the loss of motive-power which was found to occur be taken into account ; whereas in tho first series of experiments the weight of the deposited copper did not 412 ELECTRO-METALLURGY. uapuitmiai aq} jo vo co fOO O r** O O u*> 10 V) M 01 ^t- c o ino w oo ^h N I 111 aqoraurBiooriJi jaj l-t N ^) ^tvO t^ ^t N ^ jlll i jnoq aad pins 3[.toM. iei 2 5 g a) .ii c 02 " C.-W 3 a; smoq ui.rw}Oji p-i coco in Tt CTICO M CN m ON co t^ IH HI W C< M COCO^Tj-TfW !l ! ^^0^ 1 w- Vo 'M Vo "N N N t-i i-i b M M 0^ il~Jl c = 1 S3 I aq; jo Sutsu d in W t^O COCO N 00 00 ON o co co -^-oo m rf M r~-oo i>. i i IH -.*^ x ** o e 1 }J| I O ONCO OOONCOCOCOOcOt^ lllll t^ *PT)T a I b\ ON O> ON b\ N N b N Vo co 'o 'N HZ? ^^c3 HOTBOT? ut prnbii aqi g||||8888 S = ISl-gJ ^ 2 3 4> 1 "S JO SjqSlOAV l^OJ, S*.eisfefc^*^|-s| S^lss . fcrj S - r= = a, npoioinun* \O iOO OOO lOiOO 1 ^ H 2 "S M ^H- S 5 aq). jo uoiyGiAad Hi HH -111* 5-o 5 -S > aoio; CO^^N 00 N M N M O) O> C3 0> l-Sj 5 ^ aA^ouioa.oaia 1 IH 'M co rf in in o i> cb co cb c^ t> c - ?i a) C c -- oqrnnit M COO ON jo SUISI.T gq}. uopouj A"q paqiosqy -mo aq^ o^ anp asrji UT pinbTj ' -OUl!A[133 Oqj JO UOrjT?TA9Q; saratm^uao a.T^nb3 ui q^q aoisjang in Cft w OM^ M b b r^ M o o^ c?i (7i m np p CO N C> CO 00 ^- N ^C CTi CO O> 00 M " ^ in n m m vn 04 in p jn co vb co b>v M CO ^ co m r . . '007 Selly Oak Works, Birmingham . . , *o6 The purity of the deposited copper obtained by electrolysis depends upon several important conditions, either of which will greatly in- 424 ELECTRO-METALLURGY. fluence the character of the deposits ; these are : the strength and tension of the current ; the percentage of impurities in the anodes ; the altered condition of the electrolyte after dissolving out impurities from the anodes ; the distance between the anode and cathode sur- faces ; and the temperature and density of the solutions. To these points Dr. Wohlwill appears to have paid special attention, and as a consequence is accredited with producing copper of great excellence. The quality of copper is found to be uniformly pure when Mr. Sprague's limit is not exceeded. In estimating the cost of electrolytic copper refining, we have to take into consideration the interest on the capital embarked ; the cost of fuel absorbed in driving the dynamos ; the cost -of labour ; the cost of recovering sulphate of copper, &c., from the baths ; and the general expenditure of the establishment. Since many refiners are also dealers in the metal, the amount of copper in stock, as anodes, is not of so much consequence, since it is a matter of indifference to them whether it be employed as anodes or otherwise, except in the event of sudden fluctuations in the market prices, when important losses might result. The cost of fuel on the Continent is considerably higher than in Birmingham or Swansea. Upon this point M. Fontaine says : "We can estimate the cost of fuel at twenty francs per ton, although that price would be too high in the case of Birmingham, sufficiently approximate for Hamburg, and quite insufficient for Marseilles. However, as we are only making a comparison, we will maintain an uniform price ; it will always be easy afterwards to recalculate the cost, taking as a basis the actual cost of fuel in the locality con- sidered. ''An engine from 4 to 5 horse -power consumes 20 kilogrammes of fuel per hour ; the wages of the driver being estimated at 60 centimes per hour, and the necessary expenses of waste, grease, &c., at 40 centimes per hour ; the total hourly cost of the motive power is, therefore, approximately I '60 francs. A 20 horse-power engine consumes 50 kilogrammes of fuel per hour ; the driver's wages being about 70 centimes per hour, and the accessory expenses 60 centimes; total 2-30 francs per hour. The cost of maintenance and the wear and tear of the apparatus in use represent a minimum of 10 per cent, of the purchase price ; those of the building 5 per cent. The electric conductors which convey the current in the bathg do not alter in price. The labour in a factory of forty baths amounts to 75 centimes per hour, or 18 francs per day ; it is double this amount in a factory of 120 baths. The general expenditure can be estimated at 100 per cent, of the cost of labour in large installations of 200 or 300 baths, for example, and at 150 per cent, of the cost of labour in installations of only 40 or 50 baths." COST OF ELECTROLYTIC COPPER REFINING. 425 The foregoing figures (which are only approximate) enabled M. Fontaine to compile the following comparative table, which is not to be taken as absolutely correct, but as serving as a basis to a project. The figures ' ' convey an exact idea of the elements which constitute the cost of the electrolytic of refining, and their true interest consists in the comparison which they allow of being established between various factory installations : Factories taken as examples. Expenditure per ton of refined copper. Interest on capital. Motive power. Main- ten- ance. Labour. General expendi- ture. Total. Hilarion Roux, Mar- seilles frs. 78-80 64-65 35'95 frs. 112'dO 39-50 i8o'o6 frs. 18 12 30 frs. 72-00 40' o 5775 frs. io8'oo 40*00 5775 frs. 388-80 196-05 36i*45 North German Refinery, Hamburg .... Elliott Metal Company, Birmingham . . . "The cost of fuel in Birmingham," says M. Fontaine, "is much lower than we have taken as a basis ; but, taking it at 6 francs (55.) per ton at the works, we find that the motive power still costs 1-20 francs per hour, or 125 francs per ton of copper. If we leave all the other figures unaltered we obtain a total of 306-45 francs, that is to say, a much greater expenditure than at the Hamburg works. The interest on the capital engaged represents a small proportion only of the cost price, whereas at Hamburg it constitutes the main expendi- ture. As it was easy to foresee, two factories those of Hamburg and Marseilles established with the same elements, and on the same lines, give essentially different results in their working, owing to their respective magnitude. At Hamburg, where the operations are con- ducted on a large scale, the cost price of refining is about 200 francs, whereas at Marseilles, where the works are not of much importance, this cost is nearly doubled. The arrangement of 120 baths in tension, and the considerable surface of anodes, is much to be preferred to that of 48 baths of small surface, notwithstanding the enormous capital sunk in the first case. If water-power instead of steam-power were used it would still be necessary, for economically refining the copper, to adopt the disposition in use at Hamburg." "We are quite willing to endorse M. Fontaine's views as to the economical advantage of working with large anode surfaces, no matter from what source the motive power is obtained, and the observations 426 ELECTROMETALLURGY. of Keith and others clearly indicate that in this direction is to be found the chief element of economy in electrolytic refining, all other con- ditions being duly fulfilled. There can be no doubt, however, that a great deal depends upon the character of the dynamo machines manu- factured for this special purpose, and their construction should un- doubtedly be based upon the quality of copper which it is intended to refine by their agency. A dynamo that would fulfil all the require- ments of electrolysis for one variety of copper would be quite unsuited for refining metal of higher resistance. In taking advantage of this knowledge lies the secret of Dr. WohlwilTs well-known successes. Respecting the cost of electrolytic refining, the following particulars have been handed to us, from which it will be seen that there is a wide difference when compared with the estimates of M. Fontaine. Twenty indicated horse -power will deposit 3 tons of copper in 144 hours, the current being generated at a cost of 2 Ibs. of coal per horse- power per hour, thus : 2O-horse power consumes 40 Ibs. of coal per hour ; 144 X 40 5,760 Ibs. of coal per 144 hours, or, say, less than 3 tons of small coal, which can be purchased anywhere near a coal-pit at 33. a ton, delivered, or in other districts (as in Birmingham) at, say, 53. per ton. Thus the total cost of fuel for depositing 3 tons of copper by one large dynamo -electric machine amounts to only about 153. An important consideration in the electrolytic method of refining copper is, that the gold and silver which are often present in con- siderable quantities in crude coppers are entirely and easily re- coverable, since these metals, during the electrolysis of the impure material, are deposited in the mud at the bottom of the vats, from which they can be readily extracted by the ordinary processes of re- fining. As evidence of the importance of this process over the dry method of refining copper, by which small traces of gold and silver would not be recoverable we have been told that in one case, in which a trial sample of 6f tons of crude copper were operated upon by the electrolytic method, the mud from the bottom of the baths yielded 5^ ounces of gold and 123 ounces of silver, of the aggregate value of about ^"54, a sum that would leave a handsome profit after, paying the cost of the operation. It is unnecessary to say that in re- fining this sample of copper by the dry method both the gold and silver would have been practically lost. Another important consideration in the electrolytic method of refin- ing copper is, that the pure metal obtained, from its high conductivity, is invaluable for all electrical purposes, while by its aid dynamo machines may now be constructed of infinitely greater power than would have been practically possible some twenty years ago. In electrotyping, also, the, pure metal presents advantages which all ARRANGEMENT OF BATHS FOB ELECTROLYTIC REFINING. 427 practical electrotypists will readily acknowledge. In telegraphy, pure electrolytic copper presents advantages from its high conducting power which cannot well be overestimated, since even a mere trace of impurity in copper wire reduces its conductivity to a considerable extent. Arrangement of the Baths for Electrolytic Refining. A writer in the Engineer makes the following observations on the arrangement of the baths, which will be read with interest : "It is a recognised fact that when the electro -chemical action at the anode is the converse of that taking place at the cathode, an almost unlimited quantity of metal may be dissolved and deposited by the expenditure of a given quantity of electrical energy a single dynamo machine often preci- pitates over 10 kilogrammes (22 Ibs.) of copper per hour. It may be well to exemplify the fact above stated. Let us suppose that a current of 1,400 amperes is passing through an electrolytic tank, in which the anode and cathode are both of lead, and the electrolyte a suitable solu- tion of the same metal. Nearly 12 Ibs. of lead will then be deposited at the cathode per hour. If we now connect another electrolytic tank, similar to the former, in series with it, the resistance of the circuit may be nearly doubled. But if we then connect another series of two tanks in multiple arc with the former, the resistance will be reduced to its original value. Assuming that the electromotive force is not altered an assumption which is not strictly correct, but is practically nearly so if the comparatively small ' back electromotive force ' be reduced by the circulation of the electrolyte, the current will now be 1,400 am- peres, as before, and the electrical energy expended will also remain constant. But as the current is now passing through two electrolytic (double) cells in series the quantity of lead deposited will be double, i.e. 24 Ibs. nearly. Calling i current in amperes, n number of tanks in series, E electro -motive force in volts, and R resistance in ohms, the expression for weight of lead deposited per hour, applicable under the assumption above mentioned, is Pt = ~ 7 _J^ Ibs. per hour, 117 H x 117 CHAPTER XXXI. ELECTRO-METALLURGY (continued). Electrolytic Refining of Lead. Keith's Process. Electrolytic Treatment of Ores. Becquerel's Process for Treating Gold, Silver, and Copper Ores. Lambert's Process for Treating Gold and Silver Ores. Electro-chlorina- tion of Gold Ores; Cassel's Process. Electro-metallurgy of Zinc. L: - .... 6 Best red sealing-wax . . . _ . 4 Jewellers' rouge 3 The three first-named substances are to be thoroughly melted, with gentle stirring, and the rouge, which is the peroxide of iron, gradually added, and incorporated by stirring. A solution of red sealing-wax, of the finest quality, in alcohol, forma a very useful varnish for warm gilding solutions, if allowed to become thoroughly hard by drying before the article to which it is applied enters the gilding bath. Good, quick-drying copal varnish, mixed with a small quantity of jewellers' rouge, or ultramarine, is also em- ployed for hot cyanide solutions ; the same varnish, mixed with chromate of lead (chrome yellow), may be used with cold solutions. Al- most any quick drying and tough varnish may be used with cold solu- tions, and for the sake of recognising more freely the parts to which the varnish has been applied, the addition of a little mineral colouring mat- ter, as red lead, chrome yellow, or ultramarine, should be added to the varnish. The article to which the stopping-off varnish has been ap- plied, should never be placed either in a hot or cold bath, until it has become thoroughly dry and hard. The stopping-off varnishes will generally become sufficiently hard in from three to four hours in warm weather, or even in less time if the articles, after stopping, are placed in a lacquering stove moderately heated. Applying Stopping-off Varnishes. The article to be " stopped, off " must first be carefully well scratch -brushed, rinsed in hot water, and well dried by wiping with soft diaper. The parts which are to retain the silver colour (for example) are to be very carefully and neatly brushed over with the varnish, special care being taken not to spread it beyond its proper boundary, otherwise, when the article is gilt, the outlines of the various parts will exhibit a ragged and un- sightly appearance ; the work should be done by the steady hand of a skilful workman. In gilding the articles which have been stopped -off the temperature of the gold solution should be as low as possible, even when the most resisting varnishes are used. It is not advisable to 472 OPERATIONS CONNECTED WITH ELECTRO-DEPOSITION. employ too strong a current, otherwise the bubbles of gas evolved are liable to dislodge the thinner layers at the extreme edge of the varnish, whereby such parts, being denuded of the material, become coated, giving a ragged appearance to these portions of the object. After the articles have received the required deposit, they are well rinsed and dried, and the varnish is dissolved off (if an oil varnish, like copal, for example) with warm spirit of turpentine or benzole ; sealing -wax varnish may readily be removed "by methylated spirits, with the addition of heat, supplied by a hot -water bath. Another way to remove the varnish is to destroy it by plunging the article for a short time in cold concentrated oil of vitriol. In ornamenting articles, it is sometimes necessary to produce various coloured effects upon the same object, as orange yellow gold, pink and green gold, bright and dead silver, oxidised silver, &c., in which case the stopping-off needs the utmost artistic skill and delicacy of manipulation. Electrolytic Soldering. The late Frederick Scott Archer, shortly before the illness which terminated his useful career, consulted the author as to the possibility of electro -soldering the joints of a photo- graphic dipping bath, constructed with pure sheet silver. The object which the inventor of the famous collodion process had in view was to produce a bath to contain nitrate of silver solution, in which collo- dionised plates could be excited without being liable to " spots," as in gutta-percha baths. The plan we suggested, if we remember rightly, was to submit one joint at a time (the vessel having but two joinings) to the action of a double cyanide solution, rich in silver, using a "Wollaston battery of one zinc and two copper plates, and allowing the deposition to take place until the parts to be united were perfectly closed by the deposited metal. Respecting the application of electro -soldering generally, we are inclined to believe that, while it might be adopted for more effectually closing two metallic surfaces brought in close contact by covering the junction with deposited metal, we are doubtful whether an electro -soldered joint would bear any severe strain without separating. If we bear in mind that electro-deposited metals, as a rule, do not adhere firmly to their own kind, as silver to silver, copper to copper, and so on, two silver sur- faces, united by a deposit of the . same metal, can hardly be expected to form such a perfect union as would be required for a sound joint, such as is obtained with fused silver solder, for example. Some years ago M. Eisner made a series of experiments in the electro - soldering of copper, employing the Daniell battery as the source of elec- tricity. The plan he adopted was as follows : A strong ring of sheet copper was connected to the negative electrode of the battery, the ring being cut asunder at one point, leaving a gap of about iVth of an inch. The ring was immersed in a solution of sulphate of copper, and at the ELECTEOLYTIC SOLDERING. 473 end of a few days (during which the battery was kept renewed from time to time) the gap was found to be completely filled up with reguline copper. When this deposit was partially cut with a file, and the part examined with a lens, it was found to be equally filled with solid, coherent copper. Another copper ring was then cut in two parts, and the two semicircular pieces thus obtained were placed, with the faces of the sections opposite each other, in a bath and subjected to the action of the current. At the end of a few days the segments were united by the precipitated copper, again forming a perfect ring. On again applying the file to the deposited metal, so as to remove a portion of the thickness of the ring at the junctions, it was found that the' spaces had been completely filled up by the copper deposit. On examining these points with a lens, the reguline deposit of copper could be clearly traced between the filled-up spaces of the ring. A third experiment was made in the following manner : Two strong rings of sheet copper were laid with their freshly- cut faces one above the other, so that the two rings constituted a cylinder ; these rings were surrounded by a band of sheet tin, coated with a solution of wax, so that the two rings were equally surrounded by a conducting material. Thus disposed, these rings were connected to the battery, and placed in the sulphate bath. At the end of a few days the interior surface of the rings was coated with copper, the contact surfaces of the two rings being also coated with copper. These rings had only been submitted to the electrolytic action to such an extent as to cover their interior surfaces with a thin coating of copper, and yet they were completely united, and formed a cylinder in one piece. The outer rim of sheet iron was, of course, removed before testing the co- hesion of the deposit. It was remarked that these rings, after being for a certain time in the bath, in contact with the plate of copper upon which they rested, became so encrusted with copper that some force was required to detach them from the conducting wire. From these results it was concluded that two pieces of metal may be firmly united with copper by electro -deposition. To this we fully agree, provided that the united parts are not required to be subjected to a heavy strain. If a chain, for example, were composed of copper links, each united by electro -soldering, we have no hesitation in saying that, if a moderate weight were hooked on to such a chain that one or other of the links would give way, even before the copper (owing to the softness of the metal) had become stretched to any considerable extent. We do not go so far as to say that a perfect union of two copper surfaces by electro -soldering is impossible, for that such is not the case may be readily proved by trying to pull asunder the copper guiding wires from the back of an electrotype, to which they frequently adhere with great tenacity. But where a really strong joint is required we should 474 OPERATIONS CONNECTED WITH ELECTRO-DEPOSITION. certainly refuse to depend upon an electro -soldering, for the reason we have given, namely, that the adhesion of two electro-deposited surfaces cannot be relied upon. Eisner states that while conducting the above experiments, he found that when too powerful a current was employed the negative electrode, the ring, and even the copper plate upon which it rested, became covered with a dark brown deposit. After several unsuccessful attempts to prevent the formation of this brown coating, he found that it was possible to remove it entirely by dipping the article for a few seconds in a mixture of sulphuric and nitric acid, when it at once assumed the characteristic colour of pure copper. The theory of electro -soldering is thus explained : " The article is, in fact, in an electro -negative state of excitation, whilst the zinc operates positively ; the result is that the faces which are placed opposite each other when the ring has been cut are negative. During the progress of the electrolysis of the copper salt, the electro -positive molecules of copper, which are set free simultaneously, arrange them- selves upon the two opposite faces and in the direction of the break. Now from the moment these molecules are deposited, they constitute, with the piece, a homogeneous mass, and from that time act nega- tively upon the copper of the electrolyte, and again precipitate cop- per in the reguline state. This method of operation continues until the space which existed between the two separate pieces of metal is filled up with metallic copper. In fact, the layers of copper which become deposited in an equal manner upon the contiguous faces of the metal gradually diminish the distance which separated the latter, until at length the metallic layers, which cross in the opposite direc- tion, meet each other, the result being that the whole of the break which originally existed becomes filled with copper." Eisner says, with respect to the cohesiveness of the voltaic soldering, that it is the same as that of copper or other metal deposited by electrolysis ; that too strong a current must have an injurious influence on the cohesion of the deposit, as in all other cases of electro -deposition. CHAPTER XXXV. MATERIALS USED IN ELECTRO -DEPOSITION. Acetate of Copper. Acetate of Lead. Acetic Acid. Aqua Fortis. Aqua Eegia. Bisulphide of Carbon. Carbonate of Potash. Caustic Potash. Chloride of Gold. Chloride of Platinum. Chloride of Zinc. Cyanide of Potassium. Dipping Acid. Ferrocyanide of Potassium Hydrochloric Acid. Liquid Ammonia. Mercury, or Quicksilver. Muriatic Acid. Nickel Anodes. Nickel Salts. Nitric Acid. Phosphorus. Pickles. Plumbago. Pyrophosphate of Soda. Sal-ammoniac. Sheffield Lime. Solution of Phosphorus. Sulphate of Copper. Sulphate of Iron. Sulphuric Acid Trent Sand. SINCE many persons enter into the art of electro-deposition, in one or other of its numerous branches, who have not the advantage of chemical knowledge, or even an intimate acquaintance with the sub- stances employed in the various processes, a brief description of the chief characteristics of some of the more important materials may- prove serviceable. It is frequently the case, too, that lads who have been for some time occupied as subordinate assistants in the plating room, ultimately succeed to more responsible positions, and in their turn become practical platers ; to these also some information as to the nature of the substances used in the art may prove useful, and tend to guard them against error. For the sake of easy reference, the various materials will be noticed alphabetically. Acetate of Copper, or Crystallised Verdigris. This beautiful salt of copper is in dark green crystals, which are soluble in water. The common verdigris of the shops is in the form of a powder, or soft lumps of a bluish-green colour, and is insoluble in water ; it is, how- ever, soluble in dilute acetic acid, when it forms the same solution as that produced by the dissolved crystalline salt ; being richer in copper than the latter, it may be used with greater economy in making up copper solutions, or for other purposes in which the acetate of copper is employed. Acetate of Lead, or Sugar of Lead. This is a crystalline salt having somewhat the resemblance of crushed loaf sugar. The pure salt is wholly soluble in distilled water, but the ordinary commercial article frequently produces a slightly milky solution, which may be rendered 476 MATERIALS USED IN ELECTRO-DEPOSIliON. clear by the addition of a small quantity of acetic or pyroligneous acid. This salt is highly poisonous. Acetic Acid. The Acid of Vinegar. A colourless liquid, having a pungent but agreeable odour. The carbonates and oxides of most bases, as those of the metals and alkalies, are soluble in the dilute acid, forming acetates, as acetate of copper, acetate of soda, &c. Its usual adulterant is water. Aqua Fortis. See Nitric Acid. Aqua Regia, Nitro -hydrochloric Acid. This acid mixture, which is employed for dissolving gold and platinum, is made by mixing from two to three parts of hydrochloric acid, to one part nitric acid, by measure. Since aqua regia decomposes spontaneously, it should only be prepared when it is required for use. Bisulphide of Carbon. This highly volatile and inflammable sub- stance must be kept in a well -corked or stoppered bottle, in a cool place, and its vapour, when the stopper is removed from the bottle, must not be allowed to approach the flame of a candle or lamp, other- wise it may take fire and ignite the contents of the bottle, even at a considerable distance, if the apartment be very warm. Carbonate of Potash, Pearlash, or Salt of Tartar. A white granular salt employed in the preparation of cyanide of potassium, in making brassing and coppering solutions, &c. It is very deliquescent, that is, absorbs moisture from the air, and should therefore be preserved in closely stoppered jars or bottles. Caustic Potash. The ordinary commercial article, used for clean- ing metal work to be coated with other metals by electro -deposition, also for making up tinning solutions and for various other purposes connected with the art, is the substance known as American potash. This article is in the form of hard, brownish lumps, and since it readily attracts carbonic acid and moisture from the air, it must be preserved in stone jars, closed by a well-fitting bung. Caustic potash has a powerful action upon the skin, and must not therefore be handled carelessly ; when it is necessary to remove one or more lumps from the jar in which it is kept with the fingers, this should be done quickly, and the hands immediately plunged into cold water, then for a moment into a weak acid pickle, and again rinsed. A small pair of spring iron tongs should be used for taking up lumps of this caustic alkali. It may be prepared as follows : Beduce to a powder 56 parts, by weight, of fresh lime, by slaking with water. Make a cream of the powder by adding sufficient water and stirring well. Now dissolve 138 parts of pearlash in hot water, and add the cream of lime to the solution. Boil the mixture for about half an hour, or longer, and then allow it to repose. The lime will deposit in the form of carbonate CYANIDE OF POTASSIUM. 4^7 of lime, leaving- a strong solution of caustic potash, which may be preserved in a carboy until required for use. Chloride of Gold. The preparation of this substance is described in the Chapter on Gilding. Chloride of Platinum. Small fragments of platinum are placed in a glass flask, and a mixture of three parts hydrochloric acid and one part nitric acid (by measure) added ; the flask is then to be placed on a sand bath, moderately heated, until red fumes cease to appear in the upper part of the flask. The solution is next poured into a porcelain capsule, or evaporating dish, and evaporated to near dryness, the vessel being moved about until the red mass formed sets into a solid condition. It may then be dissolved in distilled water, and bottled for future use. Chloride of Zinc. Granulated zinc is dissolved in hydrochloric acid ; the liquid is then evaporated, when a semi-solid hydrated mass results, which, by continuing the heat, becomes anhydrous, and may be poured on a slab to solidify. A solution of zinc, commonly called "tinning salt," which is much used in soft soldering, is prepared by pouring muriatic acid upon small fragments of zinc, when, after the effervescence has ceased, the solution is ready for use. Cyanide of Potassium. In many respects this may be considered the most important substance used in electro -deposition, it being a powerful solvent of metallic oxides and salts. The ordinary commer- cial article is of exceedingly variable quality, and frequently contains but a small percentage of pure cyanide. Its chief adulterant is car- bonate of potash, one of its essential constituents, and therefore readily introduced in excess. In order that the user of cyanide of potassium may be fully acquainted with its composition, we will briefly explain the methods of preparing it ; and to enable him to determine the true value of the commercial article which may fall into his hands in the course of business, we will describe simple methods by which he may estimate the proportion of true cyanide ii> any given sample. Knowledge of this kind is of the utmost importance to those whose necessities or duty may require them to make up solutions of the various metals in which cyanide of potassium forms a necessary con- stituent. Preparation of Cyanide of Potassium. There are several methods of preparing this useful salt, but the process recommended by Baron Liebig is usually adopted, and is conducted as follows : 8 parts of f errocyanide of potassium (yellow prussiate of potash) are first re- duced to a powder, and then placed in a shallow iron pan, and dried at a heat not exceeding 260 Fahr., with stirring, until perfectly dry. The dry powder is next mixed with 3 parts of dried carbonate of potash, and the mixture then thrown into a red-hot crucible, and the MATERIALS USED IN ELECTEO-DEIOSITION. heat kept up, with occasional stirring with an iron rod, until the whole is fused ; the fusion must be continued until the product appears perfectly white at the end of the rod, after cooling. The crucible is then removed from the fire, the contents again stirred, and after a few moments' repose the liquid salt is poured into a clean, cold, and dry iron tray, in which it quickly sets in the form of a hard cake, which should be broken in lumps while still warm. While pouring out the clear fluid salt, care must be taken to keep back the sediment, which is chiefly iron in a finely divided state (derived from the ferro- cyanide). The sedimentary matter should be knocked out of the crucible, while still hot, upon a separate slab, and the residue of cyanide which is attached to it may be separated by dissolving it out with water. Cyanide, thus prepared, contains a portion of cyanate of potassium, but this is not injurious to the solutions of silver or other metals in which cyanide is employed. The article prepared in this way represents ordinary commercial cyanide of good quality, and it will be readily seen (since carbonate of potash is the cheapest ingre- dient) that a large excess of this salt may be employed 'without in any way affecting the general appearance of the product ; its active- ness as a solvent of metallic oxides and salts, however, will be diminished in proportion to its excess in an uncombined state. Cyanide carefully prepared by the foregoing method should contain from 70 to 75 per cent, of pure cyanide. A pure cyanide is obtained by the following process. The requisite quantity of yellow prussiate of potash, of good quality, is powdered and dried as before ; an iron crucible, having a lip, is then made red hot ; a small quantity of the powder is now introduced into the cru- cible, and when this is fused, more of the powder is added, and so on, until the vessel is about three parts filled ; the iron lid of the crucible must be put on after each addition of the powdered ferrocyanide. During the fusion of the salt there is a free evolution of gas, and the fusion must be maintained for about fifteen minutes, or until a sample on the end of an iron rod dipped into it is perfectly white on cooling. The vessel should now remain undisturbed for a few minutes, to allow the iron and other impurities to subside. The clear and colourless fluid, which is nearly pure cyanide of potassium, is now to be poured upon a cold iron slab, or into an iron pan, and the black sediment, which still retains a considerable proportion of cyanide, must be scooped out of the crucible, while still in a soft and pasty condition, and carefully preserved ; the cyanide may be dissolved from this resi- due whenever the salt is required for future use. It sometimes happens that the cyanide, from imperfect settling while in a fused state, assumes a grey shade instead of being purely white ; this is of no consequence, however, since the small proportion OF POTASSIUM. of insoluble impurities which cause this greyness will readily subside when the cyanide is dissolved in water for use. To prevent the for- mation of cyanate of potassium in the above process, some persons put a few small pieces of charcoal, and also a little powdered charcoal, into the crucible before the ferrocyanide is thoroughly fused. The cyanide obtained by this method usually contains about 96 per cent, of the pure salt. This process, however, is not so economical as the one previously given, inasmuch as a considerable proportion of the cyanogen escapes in the gaseous state, whereas, when the ferrocyanide is fused with carbonate of potash, the cyanogen unites with the potassium (the base of this salt), and carbonic acid is liberated instead. Grey Cyanide, as it is sometimes called, is commercial cyanide from which the reduced iron has not been perfectly separated ; this article is frequently preferred by some persons, since it is supposed to contain a smaller excess of carbonate of potash ; it has generally a crystalline fracture, when broken, while cyanide containing a large prepon- derance of the carbonate is of a more homogeneous structure. To Determine the Active Strength of Commercial Cyanide. The follow- ing method was suggested by the late Thornton Herapath, in The Chemist, vol. iii. p. 385 : "The first thing to be done in testing cyanide of potassium is to prepare a standard solution of ammonio- sulphate of copper or ammonio -nitrate of copper.* A certain known quantity of pure crystallised sulphate of copper, made by crushing the pure crystals of the shops in a mortar, and pressing the powder so obtained between folds of bibulous paper, is taken and dissolved in water. The solution so prepared is then to be diluted with water so as to measure 2,000, 3,000, or more water grain measures at 60 Fahr. Supposing 390-62 grains of the pure sulphate to have been taken and diluted to 2,000 grain measures, every 100 grains of such solution will, of course, represent 5 grains of metallic copper, or 6*25 grains of the protoxide of copper ; 100 grains of each of the samples of cyanide of potassium to be tested are then dissolved in a sufficient quantity of water, and introduced into the colorimeters ; an excess of ammonia is added, and the standard solution of copper is added (out of a graduated burette), to the contents of each colorimeter in turn, until a faint blue coloration makes its appearance i:i each of the solutions. The quantities of copper or of the solutions taken then indicate the relative strength and money value of the samples of cya- * Ammonio-sulphate of copper is formed by adding liquid ammonia to a saturated solution of the sulphate until the precipitate at first produced is redissolvedj when a rich dark blue solution is obtained. Ammonio-nitrate of copper is produced by adding ammonia to a concentrated solution of nitrate of copper. 480 MATERIALS USED IN ELECTRO-DEPOSITION. nide examined. Suppose, for instance, one specimen took 100 measures, and a second 150 measures, of the copper solution, the relative strengths and values of such specimens are, therefore, as 100 to 150, or 2 to 3." To render the above process available in the determina- tion of the actual strength of, or proportion by weight of, pure cyanide of potassium existing in the commercial cyanides, it is only necessary to procure a small sample of pure cyanide, and to ascertain how much of this is required to decolorise I grain of copper in the form of ammonio-nitrate. Another method of determining the proportion of pure cyanide in a given sample of cyanide of potassium is that proposed by G-lassford and Napier, which is as follows : Prepare two solutions, one of cya- nide, and another of nitrate of silver, each containing known weights of the respective salts, say I ounce of cyanide dissolved in distilled water, in a graduated glass, so as to make exactly six ounces of solu- tion by measure ; then dissolve 175 grains of crystallised nitrate of silver in about three ounces of distilled water ; add the cyanide solu- tion gradually and carefully to the nitrate solution, stirring continu- ally, until the precipitate at first formed is all dissolved without any excess of the cyanide solution. The amount of the cyanide solution required to effect this, with the above quantity of nitrate of silver, will have contained 130 grains of pure cyanide, and from the quantity used may be calculated the amount of pure cyanide in the entire ounce. The authors state that " when nitrate of silver is added to a solution of cyanide of potassium, so long as the precipitate formed is all redissolved, we obtain the whole of the cyanide of potassium in combination with the silver ; none of the other salts in solution take any part in the action, even though they be present in a large pro- portion. This enables us to test the exact quantity of cyanide of potassium in any sample." A very simple way of testing commercial cyanides where extreme accuracy is not necessary is as follows : Reduce to fine powder in a mortar about half an ounce of pure sulphate of copper ; weigh out loo grains of the powder, and dissolve (in a half -pint vessel) in about two ounces of water ; now add liquid ammonia of sp. gr. -880 until the precipitate first formed is all dissolved. Next dissolve I ounce, troy (480 grains), in about 8 ounces of water ; pour the latter solution into a tall and narrow hydrometer glass, previously graduated by pasting a strip of paper on its exterior surface, divided into ten equal divisions, and these again accurately subdivided into tenths; the solution must be diluted, if necessary, until it exactly reaches the top line or zero of the scale. Suppose we wish to determine, roughly, the comparative value of two samples of cyanide of potassium, we prepare two copper solutions as above, each containing 100 errains of LIQUID AMMONIA. 481 sulphate of copper, and dissolve I ounce of each of the cyanide sam- ples to be tested, and, taking the first sample, dissolved and poured into the graduated glass as above, we pour it gradually into one of the copper solutions, stirring after each addition, until the blue colour of the copper solution has disappeared, and has been succeeded by a pinkish tinge ; the cyanide must now be added, drop by drop, until the pink tint disappears, when the operation is complete. Now read off the balance of cyanide solution left, and make a note of it ; and after emptying the vessel and rinsing it, introduce the solution of the second sample and proceed as before, and when the decolorisation of the second copper solution is effected, note the proportion of cyanide solution which has been exhausted, and compare the two results. Dipping Acid. This name is given to a mixture of nitric and sul- phuric acids and water, with sometimes the addition of a little hydro- chloric acid, nitrate of potash, &c. The composition of various dipping acids is given in another part of the work. Fuming nitric alone is frequently used for dipping articles of copper and brass, by which they assume a bright lustre suitable for certain classes of work. Ferrocyanide of Potassium, or Yellow Prussiate of Potash. This useful salt, which is chiefly used in the preparation of cyanide of potassium, occurs in large transparent crystals of a yellow colour. The crystals must be powdered and dried at a low heat before being mixed with carbonate of potash, for the preparation of cyanide. Hydrochloric Acid, or Muriatic Acid. For most purposes the com- mercial acid is employed, but in making aqua regia for dissolving gold and platinum, the pure acid should by preference be used. Hydrocyanic Acid, or Frussic Acid. This volatile and highly poisonous substance, as obtained in commerce, is in reality a solution of the acid in water (hydrated hydrocyanic acid). The strongest form of the commercial acid, known as Scheele's Acid, contains 5 per cent, of real acid ; the dilute acid of the London Pharmacopoeia is intended to contain only 2 per cent, of real acid. Even in its diluted forms, it is an exceedingly dangerous substance to inhale, and must therefore be used with the utmost caution. Its powerful odour, resembling the flavour of the bitter almond or young laurel leaf when chewed, always indicates its presence, and the bottle in which it is kept should be very distinctly labelled, and on no account allowed to approach the nostrils when the stopper is withdrawn. The acid is affected by light, and should therefore be kept in a stone bottle, or a glass bottle covered with yellow or brown paper, and in a cool place. Liquid Ammonia, commonly called Ammonia. This highly vola- tile liquid, which consists of water saturated with gaseous ammonia, II 482 MATERIALS USED IN ELECTRO-DEPOSITION. should have a specific gravity of '880. It is usually contained in "Winchester bottles, which must be handled with great care, since the accidental breaking of a bottle of this capacity (about a gallon) might involve most serious consequences. Ammonia should always be kept in a cool place ; and when pouring it from the bottle, the user should take care to stand in such a position that the full stream of its vapours may not approach his nostrils. Mercury, or Quicksilver. This fluid metal, when pure, is bril- liantly white, and from this circumstance was called by the ancients argentum vivum and quicksilver. It emits vapour at all temperatures above 40 Fahr., and should therefore be kept in a closed bottle. It is entirely volatilised by heat, and should therefore leave no residue when evaporated from an iron spoon. If adulterated with lead, and exposed to the air, it becomes covered with a dull film of oxide, whereas if it remains bright after such exposure, the metal may be adjudged pure, since mercury in its pure state is not affected by ex- posure to the atmosphere. Muriatic Acid. Spirit of Salt. See Hydrochloric Acid. Nickel Anodes. When we state that cast-nickel anodes, contain- ing about 5 or 6 per cent, of added iron and a very large percentage of carbon, cost about fifteen years ago the enormous sum of i6s. 6d. per pound, and that almost pure anodes of nickel, either cast or rolled, may now be obtained for 33. per pound, the reader will see what a greai change must have taken place to bring about so marvellous a difference in the price of an article so indispensable to the nickel-plater. At the time we refer to, nickel was a comparatively scarce commodity, and was chiefly obtained from Bohemia and Germany . Since that period, however, nickel ores exceedingly rich in this metal were discovered in the French Colony of New Caledonia, and important improvements* have taken place both in its extraction from the ore and in its purifica- tion from the crude metal. It is, indeed, a remarkable fact in the history of the electro-deposition of this metal, that just at the time when nickel-plating was developing into an important industry, both in the United States and in this country, New Caledonia should have given up her long-hidden treasures, and supplied our markets with an abundance of this useful metal. While, a few years ago, even cast pure nickel anodes were difficult to procure, we are now able to obtain rolled nickel of any convenient thickness a most important advantage to those who desire to embark in nickel-plating upon a small scale. To Dr. Fleitmann is due the credit of having been one of the most successful in this direction, and specimens of his rolled nickel which we have had in our possession were remarkable for their purity and perfect homogeneity. Being desirous of acquainting our readers with some data respecting English NICKEL SALTS. 483 rolled nickel, we communicated with Messrs. H. Wiggin & Co., who kindly furnished us with the following particulars concerning this form of nickel anode, which will be useful to those who may wish to embark in the art of nickel-plating. The advantages claimed for rolled nickel anodes over the cast metal are : ' ' The constant and steady way in which they give off the metal ; they never become soft or fall to pieces while in the bath, as cast anodes do ; they may be light and thin to begin with (of course being far less costly in consequence) ; and they last a very long time." Nickel Salts. This term is applied to the double sulphate of nickel and ammonium, and the double chloride of nickel and ammo- nium, from which nickel-plating baths are usually prepared. The former "salts," however, are generally preferred, and may be con- sidered the best for all practical purposes of nickel-plating. Nickel salts are, like everything else in commerce nowadays, of very variable quality and price. The finest product we have yet seen was imported from the United States about 1877 78, the price of which, however, was very high. Since that period, however, the manufacture of these salts has greatly progressed in this country, and the marvellous reduc- tion in the cost of nickel has brought the selling price of the double sulphate of nickel and ammonia down to an exceedingly low figure. In reply to our inquiry upon this point, Messrs. H. Wiggin & Co., the eminent cobalt and nickel refiners of Birmingham, favoured us with the following quotations, which will serve as a guide to purchasers in large quantities. Single nickel salts, per pound, is., and double nickel salts, 9d. When we state that seven or eight years ago the price of these salts was 6s. or 73. per pound, or even more, it will be readily seen what a remarkable change has taken place in so short a period of time in this most important item of a nickel-plating outfit. In purchasing nickel salts, great care is necessary to avoid procuring an impure article, since this would involve the user in a great deal of trouble, either by yielding a deposit of a bad colour, or one that will not firmly adhere to the work coated with it. The double salts should be in large prismatic crystals of a fine dark green colour, and perfectly dry. A solution of the salt should not be acid to litmus paper. The double salt consists of I atom of sulphate of nickel, i atom of sulphate of ammonia, and 8 of water. When the commercial article is of doubtful quality, it may be improved by dissolving it in hot water, evaporating the liquor, and recrystallising. Nitric Acid. Ordinary commercial nitric acid has usually a slightly yellow tinge, but the pure acid is colourless. It is a highly corrosive acid, and freely acts upon the skin, producing yellow stains wherever it touches. This acid should never be kept in a corked 484 MATERIALS USED IN ELECTRO -DE POSITION. bottle, since it readily acts upon this substance, but in a stoppered bottle, and in a cool and dark place. Phosphorus. This substance must be preserved under water, to prevent it from coming in contact with the air, in which, even by a few moments' exposure, it is liable to inflame. The sticks of phos- phorus should be kept in a wide-mouthed, stoppered bottle, filled with water, and placed in a dark and cool cupboard. It should not be handled in the fingers nor cut in the open air, but when small pieces are required for use, it is a good plan to thrust the point of a pen- knife into one of the sticks, carefully withdraw it from the bottle, and lay it in a small dish containing sufficient cold water to cover the lump. The required piece or pieces may then be cut from the stick, and the remainder returned to the bottle by thrusting the point of the knife into it as before. Pickles. This term is applied to dilute solutions of the mineral acids, by means of which oxidation is removed or loosened from the surfaces of iron, silver, and other metals. The preparation of the various pickles, and the mode of using them, are described in the treatment of various articles for plating, nickeling, &c. Plumbago, or Graphite, commonly called Black Lead. This material, when required for electrotyping purposes, should be of the very best quality procurable. Its powder is of a dead black colour until rubbed, when it acquires a bright metallic lustre. It is commonly the practice to improve the conductibility of this substance, for electro - typing purposes, by intermixing metallic bronze powders, as copper and tin bronzes, for example, or by gilding or silvering the plumbago powder. The former is accomplished by dissolving I part of chloride of gold in 100 parts of sulphuric ether ; this is then to be intimately mixed with 50 parts of plumbago, and the mixture exposed to sun- light, being frequently stirred, until quite dry. It is then applied as ordinary plumbago, but is a very superior conductor. Fyrophosphatc of Soda. This salt, which has been much used, especially in France, in the preparation of gilding baths, may be readily prepared by heating common phosphate of soda to redness in a crucible, when it parts with its waters of crystallisation, and becomes anhydrous pyrophosphate. Dissolved in hot water this anhydrous (that is, free from water) salt yields permanent crystals on cooling, which contain 10 atoms of water. These crystals are not so soluble as the common phosphate, and their solution precipitates nitrate of silver white (pyrophosphate of silver), and has an alkaline reaction. All the insoluble pyrophosphates, including that of silver, are soluble to a certain extent in the solution of pyrophosphate of soda, hence the usefulness of this salt in preparing gilding solutions. Sal-Ammoniac, or Chloride of Ammonium. This salt occurs in the SULPHATE OF COPPER. 485 form of crystalline lumps, which being exceedingly tough, are more readily broken by forcing a sharp steel point through the mass by means of a hammer than by the ordinary means of crushing or pul- verising. When broken into small fragments in the way indicated, the salt may more easily be reduced to a more or less powdery condition. Sheffield Lime. This material, which is preferred by brass and nickel -plate finishers to any other kind of lime, is obtained from the neighbourhood of Sheffield, from whence the lumps are carefully selected and transported in wooden casks to London and other parts of the kingdom. The lime must be kept rigidly excluded from the air, otherwise it attracts carbonic acid, forming carbonate of lime, by which it loses its cutting property and becomes useless. Small quantities may be preserved for any length of time in stone jars, closed by a tight-fitting bung, but for larger quantities olive jars and grocers' large tin canisters have been used with advantage. Solution of Phosphorus, or Greek Fire. This preparation, which consists of phosphorus dissolved in bisulphide of carbon, is not only highly inflammable, but if any of it be accidentally dropped upon the clothes or floor, it is very liable to take fire spontaneously. It should only be prepared in small quantities, and the bottle in which it is kept should be partly immersed in sand in an earthenware vessel, covered with a metal lid, and placed in a cool situation. Sulphate of Copper, or Bluestone. It is of the greatest impor- tance that this substance, whether employed in electrotyping or for any other purpose connected with electro -deposition, should be per- fectly pure. The pure sulphate occurs in large crystals of a rich deep blue colour. If there be any green salt in the interstices of the crystals, this is due to the presence of sulphate of iron, or copperas, and the article should therefore be rejected. The " bluestone " of the shops is frequently contaminated with copperas. To determine the presence of iron in a sample of sulphate of copper, dissolve a small quantity of the salt in distilled water, then add liquid ammonia, stir- ring with a glass rod until the precipitate formed becomes entirely dissolved. Allow the blue liquid thus obtained to rest for a short time, then pour off the clear liquor and add distilled water to the sediment ; after a while pour off the water and add a little hydro- chloric acid to the residuum ; allow the acid to react upon the deposit for a few minutes, then pour into the acid liquor a few drops of a solution of ferrocyanide of potassium, when, if a blue colour is pro- duced (prussian blue), this proves the existence of iron in the original sample of sulphate of copper. Sulphate of Iron, Copperas, or Green Vitriol. A bright sea-green crystalline salt, readily affected by exposure to the air; it should therefore be kept in a well-corked bottle or jar. The crystals should 486 MATERIALS USED IN ELECTRO-DEPOSITION. be bright, perfectly dry, and free from red or brown powder (peroxide of iron). The presence of this powder, however, is not of much con- sequence, since, being insoluble in water, it will readily deposit to the bottom of the vessel when the crystals have been dissolved. Sulphuric Acid, or Oil of Vitriol. The ordinary commercial acid has usually a somewhat brownish tint, owing to small quantities of straw or other organic matters accidentally falling into the carboys in which it is conveyed. The pure acid is, however, colourless. This acid should be kept in a perfectly dry situation, since it attracts moisture from the air ; and when making a dilute solution of the acid, it should be added gradually to the water, and not the water to the acid, since this might cause the mixture to explode with very disastrous results. Trent Sand. Glass Cutters' Sand. These materials are used by brass polishers in the earlier stages of the polishing process, to remove file-marks and other irregularities from the metal work, the latter substance being used for articles in which a very keen- cutting material is necessary. CHAPTER XXXVI. USEFUL INFORMATION. Driving Belts. Chutter's Dynamo-electric Machine. Quantity of Elec- tricity and Electro-motive Force. Management of Dynamo-electric Machines. Management of Batteries. Relative Power of Batteries. Constancy of Batteries. Relative Intensity of Batteries. The Resistance Coil. Speed Indicator. Binding Screws. Characteristics of Metals. Test for Free Cyanide. Oxidising Copper Surfaces. Alloys. Solder- ing. Soldering Liquid. To remove Soft Solder from Gold and Silver Work. Platinising. Steel-facing Copperplates. Antidotes and Reme- dies in Cases of Poisoning. Driving Belts. Most users of dynamo machines, polishing lathes, and other machinery driven by steam-power or gas-engines, will have experienced some trouble from the breaking, slipping, or slackening of the driving belts. Since a few hints upon these matters may prove acceptable, we give the following extracts from an exceedingly inter- esting and thoroughly practical paper, by Mr. John Tullis, of St. Ann's Leather Works, Glasgow.* Main Driving Leather Belts should be manufactured so that when the joint is made while the belt is in its place, it ought to present the appearance of an endless belt. After having ' been taken up once or twice during the first year, good belts such as these require very little attention during the subsequent years of their long life. If the belt is driving in a warm engine-room, it ought to get a coating of curriers' dubbing three tunes a year. All belts having much work to do ought to present a clammy face to the pulley, and this condition can be best maintained by applying one coating of dubbing and three coatings of boiled linseed oil once a year. This oil oxidises, and the gummy surface formed gives the belt a smooth, elastic driving face. A belt looked after in this way will always run slack, and the tear and wear will be inconsiderable. On the other hand, dry belts have to be kept tighter, because they slip and refuse to lift the work. The friction of the running pulley " burns the life " out of the belt while this slipping is going on. * Scottish Leather Trader, July, 1885. 488 USEFUL INFORMATION. Fixing the Belt. As to which side of the leather ought to be placed next the pulley, Mr. Tullis says, < ' It is well known that by running the grain or smooth side next the pulley, there is considerable gain in driving power. However, by using boiled linseed oil, as before men- tioned, fheJZesh side will soon become as smooth as the grain, and the driving power fully as good. A belt working with the grain side next the pulley really has a much shorter life than the belt running on the flesh side. The reason is, the one is working against the natural growth of the hide, while the other is working according to nature. ... If you take a narrow cutting of belt leather, pull it well, and lay it down, you will at once observe that it naturally curves flesh side inwards. Nature, therefore, comes as a teacher, and tells us to run the flesh side next the pulley, and practice proves this to be correct." Jointing Belts. "Whether the belts are new or old, a properly made joint is of the first importance to all users of belting. ... A well-made butt joint, with the lace holes punched in row of diamond shape, answers the purpose fully as well as any. Care should be taken that the holes do not come in line across the belt. A good lace, properly applied, with all the strands of the lace running lengthwise of the driving side of the belt, will last a long time and costs little. If a lap joint is made, time should be taken to thin down the ends of the lap. Joints of this sort should be made to the curve of the smallest pulley over which the belt has to work." Accumulation of Lumps on Pulleys and Belts. Dust should never be allowed to gather into a cake either on pulley or belt, for if so, the fibre of the leather gets very much strained. The belt is prevented from doing its work because this stranger defies the attempts made by the belt to get a proper hold of the pulley. Belts and Ropes coming off Pulleys. When a bearing gets heated, the shaft naturally becomes heavy to turn. The belts or ropes, having already the maximum of power in hand they are designed to cope with, they refuse this extra strain, and will leave the pulleys at once, or break. This accident directs the attention of those in charge to the belts or ropes, when time is taken up in consulting as to what is to be done. Meanwhile the cause of all the trouble gets time to cool, and the source of annoyance is never discovered. Before a new start is made, all bearings are well lubricated. All goes smoothly, yet some one is blamed for the break down. The above hints, coming as they do from an experienced manufac- turer of leather, and who is also an extensive user of belting, will be invaluable to those who, though constantly using driving belts, may be unacquainted with the principles of their action. Chutter's Dynamo-electric Machine. Since the earlier portion CHUTTER'S DYNAMO-ELECTRIC MACHINE. 489 of this work was written, we have been favoured by Mr. Samuel Sykes, of Birmingham, with some particulars concerning Mr. George F. Chutter's dynamo -electric machine, which we feel bound, in the interest of our readers, to publish, more especially since the new machine appears to have been used somewhat extensively, giving great satisfaction, by platers and gilders, and also by nickel -platers in Bir- mingham and its neighbourhood. The principal features of this machine, and its capabilities, are stated as follows : The small machine (No. 3 size), Fig. 133, which absorbs about Fig. 133- 2 horse -power, will, under favourable conditions, deposit about 2O ounces of silver per hour. " The armature, spindle, and commutator are made in one malle- able casting, and very great care is exercised in the selection of these castings, any one casting which may be found to be harder than the best wrought iron being rejected. The bearing extents of the spindle are cased with hardened steel sleeves, which, as they are made inter- changeable, can be renewed at a small cost, thus saving the weaken- ing effects of wearing down and tearing up the spindle itself. The total height of this small machine is 10 inches ; extreme length, 17 inches, and weight, 63 pounds. The commutator is cased in phos- phor bronze, which is found to be more durable than copper, which is generally used. The machine being of open structure, allows a free circulation of air through it, which prevents undue Seating, while its compactness allows it to occupy a small space." The efficiency of the machine is said to lie in its simplicity, and the careful balancing of the parts in the design. 490 USEFUL INFORMATION. Amongst those who have applied the No. 3 size machine, above referred to, is Mr. Smith, of Branston Street, Birmingham, who employs 220 feet main leading circuit round his plating shop, wires being taken off to gilding and silvering vats every few feet along its length, by which arrangement the smallest article of jewellery can be gilt, and heavy deposits of silver put upon cruet-frames, salvers, &c. at the same time each workman using the current from the main leading wires with perfect steadiness, irrespective of what is being done in other vats. The Chutter machine has also been adopted by Mr. James Fenton, Mr. J. M. Davis, Mr. Daniel Griffin, and others, of Birmingham, who have warmly testified in its favour. It appears to have given much satisfaction in electro -brassing cast iron. Quantity of Electricity and Electromotive Force. The power of a given quantity of electricity to do a certain amount of work in a given time, depends upon how much of the current which the battery or machine is capable of generating actually passes into the electro- lyte or depositing solution, and this will depend I, upon the nature of the electrolyte ; 2, the temperature of the liquid ; 3, the distance between the anodes and cathodes ; and, 4, the density of the solution. As a rule, acid solutions are better conductors of the current than alkaline solutions, or, in other words, they offer less resistance to its passage through the liquid. Hot solutions are better conductors than cold ones, and the closer the anodes and cathodes approach each other the less distance has the current to traverse through the liquid in its passage from the former to the latter. While a single battery cell would be sufficient to deposit copper freely from a solution of the sul- phate, three such cells would be required to deposit an equivalent of silver from a cyanide bath, and double that number, coupled in series, to deposit brass or copper from cyanide solutions. When the battery cells are arranged in series, that is, the positive element of one cell connected to the negative ele- ment of the next cell, and so on, the power of the current is greatly augmented, because it can pass more freely, that is, the electro- motive force of the combined series p. j urges forward the current generated in each cell, and thus enables the compound battery to do more work than if the negative and positive wires were separately grouped in " multiple arc," as in Fig. 134. MANAGEMENT OF DYNAMO-ELECTRIC MACHINES. 491 The amount of current which a battery is capable of generating, however, depends upon the surface of the positive element (zinc) immersed in the exciting fluid of the cell, and the weight of zinc dissolved in a given time, which is exactly equivalent to the weight of metal deposited in the bath ; moreover, the amount of zinc dis- solved in a given time is exactly the same in each cell, and if one zinc element in a series of six cells were smaller than the other five, the actual amount of available power of each cell of the series would be reduced to the capacity of the smallest zinc element. Management of Dynamo-Electric Machines. In working a dynamo or magneto -electric machine, it is of the greatest importance that, as far as may be possible, it should be allowed to run at an uniform speed. This important point is seldom reached when steam- power is obtained from a source which supplies power to other pre- mises or parts of the same building, as is frequently the case, both in London and the provinces. Moreover, when the same engine which gives motion to the polishing lathes also drives the dynamo machine, irregularities of speed frequently occur, more particularly when there happens to be some especially severe strain upon the polishing spindles, as in sanding rough and heavy pieces of work. There can be little doubt that gas-engines, from the uniformity of their action and the readiness with which power can be obtained from them, regardless of their superior economy, are most suitable for driving dynamo machines ; indeed, if it were not for these useful motors, it is doubtful if the applications of dynamo -electricity to the deposition of metals and electric lighting would have attained their present develop- ment. Being of opinion that the gas-engine and dynamo -electric machine form the most perfect combination for obtaining electricity for the purposes of electro -deposition under the most favourable con- ditions of economy, convenience, and regularity, we applied to Messrs. Crossley Brothers, of Manchester, for some particulars of their " Otto " engine, which we had frequently seen driving dynamos, while performing other work, such as driving polishing- spindles, scratch -brush lathes, &c., and through the courtesy of those gentlemen we are enabled to give the following details, which will be useful to such of our readers as may contemplate adopting magneto or dynamo -electric machines as substitutes for voltaic batteries, or those who may desire to possess economical motive - power of their own rather than bear the ills of an irregular and often costly supply of hired steam-power from adjacent premises. An illustration of a 6 horse -power "Otto" gas-engine is given in Fig- 135- Advantages of the Gas-Engine in driving Dynamo Machines. These 492 USEFUL INFORMATION. may be briefly summed up as follows : The engine can be started in a minute's time ; the lubricating- being done by a self-acting arrangement, little or no further attention is required until the en- gine requires to be stopped, which is effected by simply shutting off the gas. The attendance required seldom exceeds one hour a day, and this is only needed for oiling, cleaning, and starting the engine. There being no risk from boiler explosion, the leading insurance com- panies do not change extra insurance where gas-engines are employed. Mr. F. T. Linton, of the Leith Gas "Works, in. a paper upon this subject,* says, in reference to a 3! horse-power " Otto " engine, which had been adopted at the works: "It is employed to drive various machines in our workshops, such as Hoot's blower for three smiths' fires, a large screw -cutting lathe, a screwing machine, a, drilling machine, a circular saw, two smaller lathes, and two grindstones. The amount of power required varies considerably, as at one time nearly all these machines may be in use, and at another time not more than two or three of them. In all cases, however, the smoothness and regularity with which the engine works are very noticeable there being no sensible diminution or acceleration of speed as the different machines are put in or out of action." This important feature in these machines renders them, as we have before observed, specially applicable to the purposes of the electro-depositor, who requires not only to drive his dynamo, but also his polishing spindles, emery- wheels, scratch-brushes, &c., and this without interfering with the steady speed of his most important appliance the source of elec- * Engineering, July soth, 1880. GAS-ENGINES. 493 tricity. Regarding the comparative cost of working gas and steam engines, Mr. Linton's paper contains some very interesting data, from which we extract the following : Taking a gas-engine and a steam-engine of the same horse-power that is, each being of 3^ nominal horse -power after estimating the working expenses of each, as also the wear and tear and depreciation, the total annual charge would be For the gas-engine . . , . 52 8 6 For the steam-engine . . 79 6 o Showing a considerable advantage in favour of the gas-engine, irrespective of the other advantages we have endeavoured to point out. Overheating of Dynamos. Some dynamo machines are so con- structed as never to become heated while at work ; others, on the contrary, are kept cool by means of a stream of water passing through such parts as are liable to become heated. In this latter case the plater should occasionally place his hand on the machine to ascertain if it be overheated, through failure of the water supply or other cause ; on no account should this be neglected, otherwise the machine may suffer serious injury. Lubrication, Cleanliness. The bearings must be kept well lubricated with oil, and great care taken to prevent dust working into these parts of the machine. The divisions between the segments of the commutator of a "Weston machine should also be kept clean, by passing a strip of card along these grooves to clear away the particles of metal which wear off the brushes and the commutator itself. When the brushes consist of layers of thin sheet copper, the ends should be trimmed with shears occasionally when much worn. Slipping of Belts. It sometimes happens that the driving belts are liable to slip off the pulley of the machine, owing to the belt being slack or not running perfectly true ; sometimes this will occur when the machine is put on short circuit either accidentally or to exhibit its spark. When liable to this defect more especially if it arises from imperfect fixing of the machine, or want of truth in either its own pulley or the driving pulley it is a safe plan to fix an iron fork in such a position that it will keep the band from slipping off the machine pulley under any circumstances. Acid Fumes. Wherever dynamo machines are employed it should be strictly forbidden to allow any fuming acid, as nitric and hydro- chloric acids or dipping acids, to be used in the room in which the machine is placed, of course excepting the hydrochloric acid dip, which, being used in a diluted form, will be unobjectionable. The machine should not be fixed in such a position as to be near the 494 USEFUL INFOBMATION. polishing shop (as we have frequently known to be the case), since the floating particles of lime, cotton from the dollies, and other floating matter will probably find its way into the interior of the apparatus and eventually do mischief. Management of Batteries. The zinc plates must always be kept well amalgamated ; if the operator feels a tickling sensation in the throat, causing him to cough frequently, he may generally attribute this to the excessive evolution of hydrogen from one or more of his battery cells, which is very irritating to the air passages of the lungs. In such a case he should at once look to his batteries, and the defective cell, which will exhibit a brisk action or effervescence, with evolution of heat, must be disconnected, and the zinc withdrawn and reamal- gamated. Before doing so, however, he should examine his connect- ing wires, to see if the battery is " short circuited " at any point by the accidental contact of the electrodes or other conductors. It is also very necessary that all binding screws or other connections should be scrupulously clean at the points of contact, as also the ends of the connecting wires which are adjusted to the binding screws. The upper ends of the carbons used in Bunsen batteries should be var- nished, or coated with melted paraffin wax to prevent the nitric acid from attacking the brass clamps, and thus not only injuring them, but causing defective connection. The copper plates of "Wollaston batteries should be kept clean ; if accidentally spotted with mercury, from contact with the amalgamated zinc plates, the sheet copper should be heated to expel the mercury, then pickled in dilute sulphuric acid, and, after rinsing, be well scoured. The zinc rods of Daniell batteries should never be allowed to rest on the bottom of the porous cells, or a deposit of copper may take place both inside and outside the cell and render it useless. Porous cells often crack from this cause. When porous cells which have been used are laid aside until again required for use, they should first be well rinsed and then filled with clean water. They should never be allowed to become dry, otherwise any sulphate of zinc remaining in their pores will crystallise, and pro- bably in doing so crack the vessel in many places. Relative Power of Batteries. The following experiments, made with electrodes double the size of the zinc plates of the batteries, all at equal distances (one inch) apart, will show the relative power of batteries. The time in action was one hour each ; only one pair of plates constituted the battery : Deposited Grove battefy . . 104 grains. Single-cell apparatus . 62 Deposited Smee battery . . 22 grains. Wollaston . 18 , Daniell battery . . 33 Constancy of Batteries. The action of most batteries differs after KELATIVE INTENSITY OP BATTERIES. 495 the first hour, so that one kind of battery may be useful for a short period, and another kind if the action is to be sustained for any length of time. This is illustrated by the following table, the conditions being the same as in last experiment, or on this being continued and the results taken every hour for seven successive hours : One hour. Two hours. Three hours. Four hours. Five hours. Six hours. Seven hours. Total. Grove battery 104 86 66 60 54 49 45 464 grs. Single-cell . 62 57 54 46 39 29 4 3u Daniell 33 35 34 32 32 30 3i 227 Smee . 22 16 14 II 12 II 10 96 Wollaston . 18 H 15 12 II 10 10 20 To make this comparison more practical, larger plates were used for the battery, and proportionately larger electrodes, and the battery was kept in operation until one pound of copper was deposited, the acid being renewed and the zincs brushed every twenty-four hours. The time taken to effect this was : Grove battery . Single-cell Daniell . hours. 45 49 Smee battery Wollaston. . 147 hours. Relative Intensity of Batteries. Different batteries have different degrees of power to overcome resistance, that is, greater intensity, or higher electromotive force. To demonstrate this a single pair of "Wollaston, Smee, and Grove batteries were fitted up as nearly equal in circumstances as the different arrangements would allow. Each cell exposed the same surface of zinc, and was connected with electrodes immersed in a solution of sulphate of copper, first one inch, then two, then three and four inches apart for half an hour in each case. They were then reversed, beginning with the electrodes at four inches, and coming to one inch. These experiments were repeated several times, and a mean of the whole taken. The results were : Electrodes. Deposited. Wollaston Smee. Grove.' One inch . 8' 8 grains. i2'o grains. 31-0 grams. Two inches . 6-6 6'8 26-0 Three 4'7 6-0 i?*o ,, Four 3-o 4'6 14-0 From this it will be seen that "Wollaston stands lowest in intensity, which is more apparent as the distance of the electrodes is increased 496 USEFUL INFORMATION. Smee is one-third more than Wollaston at one inch, and one-half more at four inches, while Grove is three-and-a-half more than Smee at one inch, but frur-and-a-half more than Wollaston and three more than Smee at four inches. Taking the mean results as a comparison of batteries, their value will stand as under : One pair. Two pairs. Four pairs. Six pairs. Nine pairs. Grove battery 55 ,72 93 97 98 Daniell . 15 35 60 77 86 Smee . ii 19 29 4i 58 Wollaston 8 15 24 33 48 The above table gives results approaching to and in principle the same as the others ; it will be observed that one pair of Groves is equal to nine pairs of either "Wollastons or Smees. It is also notice- able that Grove's increases slowly in quantity above four pairs, the intensity being sufficient at four pairs to overcome the resistance offered to the current of electricity. For ordinary electrotyping, in- tensity arrangements are unnecessary, except when the article upon which the deposit is being made is of such a character as will not allow the positive electrode to be brought close to it, or when there are deep- cut objects, or any circumstance which increases distance or requires power to overcome resistance. The Resistance CoiL Where magneto or dynamo -electric ma- chines are employed, it is absolutely necessary to have at command some means of controlling the current, especially while the baths are being filled with work. For this purpose various contrivances have been suggested, but the simplest form of apparatus, and at the same time one of the most effectual, is that shown in Fig. 136. It consists of a mahogany or cedar board, about 1 8 or 20 inches by 12 inches, or even of larger dimensions, upon which a coil of brass or German silver wire is stretched by means of brass nails or pins. A movable key, furnished with a handle, is screwed to the lower part of the board, and which, when turned to the left or right, traverses the semi- circular row of pins, by which the force of the current is allowed to enter the coil of thin wire to a greater or less extent according to the direction of the movement. For example, by moving the key to s (strong), the full current passes into the plating vat ; if the key be moved from peg to peg to the right, in the direction of w (weak), the current enters the thin wire, which resists its passage in proportion to the length of wire which is thus interposed in the circuit. The two binding screws at s and w are for connecting the resistance coil with the machine and the plating vat, which is done by attaching a RESISTANCE COIL. 497 Fig. 136. short length of stout copper wire to the binding screw at s, the other end being connected to the cathode suspending rod of the bath. A similar piece of wire connects the binding screw w with the negative pole of the dynamo -electric machine. When the key is shifted to w the current entering the bath is reduced to a minimum. In starting the in- strument, therefore, especially when small articles are to be put into the vat, the key should be placed on the first peg at w, and this must be shifted on to the next peg, and so on, as the bath becomes filled with work. It is very important that the wires of the coil should be placed and kept at some distance from the board, other- wise, when the full amount of resist- ance to the current is effected, the heat of the wires which become red- hot are liable to burn the board, a circumstance which has frequently occurred. The brass pins, or screws, for supporting the wire, should be long enough to keep the wire at least three-quarters of an inch from the surface of the board. If the wires become shifted at any time, so as to approach the board, they must be readjusted by being brought up close to the heads of the pins. The heads of the lower pegs should be cleaned with emery cloth each morning before the resistance coil is put into use, so as to insure a clean connection for the movable key. Speed Indicator. A very useful and, indeed, necessary instru- ment for those who employ power-driven machinery, as dynamo-elec- tric machines, for example, is the speed indicator, Fig. 137, by the employment of which the number of revolutions made by the armature per minute may be readily de- termined. The instrument being held in the right hand, its point is inserted in the small hollow at the end of the spindle to which the small pulley of the dynamo is attached, the time being taken by the seconds hand of a watch, held in the left hand. These indicators may be obtained from any machinist at a moderate price, and may be had to indicate up to 1,000 revolu- K 1C - 498 USEFUL INFORMATION. tions. The instrument shown in the figure indicates, as will be seen, up to 100. For pointed centres, such as polishing spindles, the little cap on the left of the cut is adjusted to the point of the indicator. This handy instrument can be conveniently carried in the waistcoat pocket. Binding Screws. These useful and necessary appliances are usually made from cast brass, and may be obtained in a great variety of forms. A few examples are shown in the accompanying engravings. Fig. 138 is used for connecting the platinised silver of a Smee battery to the Fig. 138. Fig. 139- Fig. 140. Fig. 141. wooden cross-bar, or for casting in zinc bars f or Daniell's battery ; Fig. 139 is used as a connection for a zinc or flat carbon plate ; Fig. 140 is a binding screw for zinc plates, or for the cylinders of a Bunsen battery ; Fig. 141 is for uniting the poles of dynamos with leading rods ; Figs. Fig. 142. 143- Fig. 144. 142, 144 are for connecting flat copper bands to zinc and platinum plates, as in Grove's battery ; Fig. 143 is a clamp for large carbon blocks, for uniting the zincs of a Smee, or the copper plates of a Wol- laston battery. Characteristics of Metals. To those who are engaged in manipulating metals, a knowledge of their chief attributes is always useful, and sometimes absolutely necessary. The subjoined data will therefore, it is hoped, prove acceptable. Malleability. When plates or bars of metal are hammered or passed between heavy rollers, they exhibit variable powers of retaining their cohesion as the metal passes into the form of a thin sheet or "leaf." TEST FOR FREE CYANIDE. 499 Of all metals, gold is the most malleable, being capable of being beaten out so thin that the leaf is only i-28o,ooothof an inch in thick- ness, while a square foot weighs only 3 grains. Dwtility.The property of being capable of extension by being drawn into wire, is greatly different in the various metals, gold being not only the most malleable, but also the most ductile of all metals. A single grain of gold can be drawn into a wire 500 feet in length, and the diameter of the thinnest platinum wire does not exceed i-3o,oooth of an inch. In drawing these fine wires of gold or platinum, the metals are covered with a cylinder of silver, and both are drawn together, and thereafter the outer silver coating is dissolved away by nitric acid. Tenacity. The strength or cohesive power of the metals, which enables them to sustain greater or less weights, is spoken of as their tenacity. A bar or wire of the metal is securely suspended from a vice or other fixture, and weights are attached to the lower end till the wire parts or breaks. Iron possesses the greatest tenacity, and the following table gives the relative weights which several of the metals will suspend : Most Malleable. Most Ductile. Most Tenacious. Gold. Gold. Iron. Silver. Silver. Copper. Copper. Platinum. Palladium. Platinum, Iron. Platinum. Palladium. Copper. Silver. Iron. Palladium. Zinc. Aluminium. Cadmium. Gold. Tin. Cobalt. Tin. Zinc. Nickel. Cadmium. Lead. Aluminium. Lead. Cadmium. Zinc. Least Tenacious. Nickel. Tin. Cobalt. Lead. Least Malleable. Least Ductile. Test for Free Cyanide. It is sometimes useful to have at com- mand some ready way of determining the actual quantity of free cyanide in a solution. For this purpose Mr. Sprague devised the fol- lowing system, " based upon the ordinary decimal measures obtainable anywhere, and upon the basis of one ounce of cyanide per gallon of solution, from one to two ounces being the proper working strength." The method is thus described : " One ounce per gallon is equal to 62-5 grains in 10,000 ; the equivalent of cyanide of potassium is 65, and it takes two of these to precipitate and redissolve cyanide of IJOO USEFUL INFORMATION. silver from nitrate of silver, the equivalent of which is 170. The tent solution, therefore, is prepared from pure nitrate of silver, 81-72 grains, dissolved in a 10,000 grain flask of distilled water ; 8' 172 grammes in a litre make the same solution, which is equivalent, bulk for bulk, to a solution of one ounce of cyanide hi a gallon, and may be used in any measure whatever, properly divided. I prefer to take 1,000 grains of it, and make it up to 10,000 again ; to take loo grains of the solution to be tested, by means of a graduated pipette, and then add this weaker solution to it from an ordinary alkalimeter. As soon as the precipitate ceases to redissolve on shaking, the test is complete. A slight cloudiness in the liquid marks this point. " To test a sample of cyanide, dissolve 62^ grains in the 10,000 grain flask, and treat this in the same way. Thus, if a sample is so treated, 100 grains placed in a small flask or bottle, 1,000 grains of the test put into an alkalimeter and dropped into the flask as long as the precipitate disappears, and if upon adding 520 grams in this way, a permanent faint cloudiness is produced, the sample contains 52 per cent, of real cyanide. Kdthe original test solution is preferred, 1,000 grains of that kj^]g^^i must be used, and the result is the same." OrtdipinfccJtKpfer Surfaces. To produce a deep black coloration upon tudeaned copper surface, dissolve from TOO to 150 parts of hydrous carbonate of copper in a sufficient quantity of liquid am- monia. The cleaned articles are promptly immersed in this solution, when they immediately become coated with a fine black deposit, which, when burnished, has the appearance of a black varnish. Sulphide of Barium. We have found that a rich coloration may be given to clean copper articles by immersing them for a longer or shorter period, according to the effect desired, in a dilute solution of sulphide of barium. About 4 or 5 grains of the salt to each ounce of water produces an instantaneous coloration, of a warm bronze tint, which increases in vigour by longer immersion. The action is of so permanent a character that the articles will bear much friction before the coating will yield, while the warm chocolate tone which the metal assumes has a bright metallic lustre which, for some surfaces, is exceedingly pleasing. Alloys. In pursuing the art of electro-deposition the operator has greatly to deal with alloys of metals ; and since the various kinds of alloy, as brass, gilding metal, German silver, and bronze, for example, differ considerably in their composition, it will be useful to the electro- depositor to have some general knowledge of the constitution of the various alloys which may come into his hands to be coated with gold, silver, or other metallic deposit. Formerly the term alloy signified a compound of gold and silver combined with some inferior metal ; it is now understood to mean a compound of two or more metals of any ALLOYS. 501 kind. For example, brass is an alloy of copper and zinc, and bronze an alloy of copper and tin. An alloy composed of metals which differ in their fusibility are usually malleable when cold, and brittle when hot, as is the case with brass. Many alloys consist of the definite or equivalent proportions of the metals, while other alloys seem to form in any proportion ; the finest quality of brass is obtained when the respective metals, copper and zinc, are combined in their atomic or equivalent proportions. One metal does not alloy itself indifferently with every other metal, but is governed in this respect by peculiar affinities : thus silver will hardly unite with iron, but it combines readily with gold, copper, and lead. In comparing the alloys with their constituent metals, the following differences may be noted ; in general, the ductility of the alloy is less than that of the separate metals, and sometimes in a very remarkable degree ; on the contrary, the alloy is usually harder than the mean hardness of its constituents. The mercurial alloys, or amalgams, are, perhaps, an exception to this rule. The specific gravity is rarely the mean between that of each of its constituents ; but is sometimes greater, and sometimes less, indi- cating, in the former case, an approximation, and in the latter a recedure, of the particles from each other in their act of union. ( Vre.} When there is a strong affinity between the two metals, the density of their alloy is generally greater than the calculated mean, and vice versa y as illustrated in the following table : ALLOYS HAVING A DENSITY Greater than the mean of their Less than the mean of their constituents. constituents. Copper and bismuth. Gold and copper. ,, palladium. , , iridium. ,, tin. , , iron. ,, zinc. lead. Gold and antimony. nickel. , , bismuth. silver. ,, cobalt. Iron and antimony. tin. ,, bismuth. ,, zinc. lead. Lead and antimony. Nickel and arsenic. Palladium and bismuth. Silver and copper. Platinum and molybdenum. Tin and antimony. Silver and antimony. lead. ,, bismuth. ,, palladium. ,, lead. Zinc and antimony. tin. , , zinc. 5O2 USEFUL INFORMATION. Dr. Ure says, "Every alloy is, in reference to the arts and manu- factures, a new metal, on account of its chemical and physical pro- perties. A vast field here remains unexplored. Not above sixty alloys have been, studied by chemists out of many hundreds which have been made ; and of these very few have yet been practically employed. Very slight modifications often constitute very valuable improvements upon metallic bodies." Since those words were written, however, many important alloys have been introduced, while at the present time the subject is receiving considerable attention not only in this country but also in the United States. When it is desired to alloy three or more metals, as in the manu- facture of German silver, which is composed of copper, nickel, and zinc, much difficulty would arise if we attempted to fuse all the metals together at one time, since the zinc, being more readily fusible than the other metals, and at the same time volatile, would simply pass away in vapour : the least fusible metal (nickel) should therefore be first brought to a state of fusion, the copper then gradually added, and the zinc finally introduced in the same cautious way. Again, in forming certain kinds of brass, in which a small quantity of lead forms a constituent, the copper should be melted separately, the zinc and lead then melted together, and the alloy next added to the copper, or vice versd, the combined metals being then fused together until the combination is complete. In combining zinc with copper, to form brass, the metals are first melted separately, and then quickly mixed while in a state of fusion. Brass is sometimes formed by adding strips of copper to molten zinc, until an alloy, not easily fused, is formed. This is afterwards broken up into fragments, and remelted under a layer of charcoal, with the addition of either metal to bring the alloy up Co the colour and standard required. It appears that the best proportion of metals to form fine brass is one prime equivalent of copper = 63 -\- one of zinc = 32-3, or very nearly 2 parts of copper to i part of zinc. The bright gold -coloured alloy called Prince's or Prince Rupert's Metal consists of 2 parts zinc to I part copper. The principal alloys of metals employed in commerce are shown in the following table : Names. Combining Metals. Albata, or German silver . Copper, nickel, and zinc, with, some- times, a little iron and tin. Aluminium bronze . . . Aluminium and copper. Amalgams .... Mercury and other metals. Bath metal .... Copper and zinc. Bell-metal .... Copper and tin. Brass Copper and zinc. Britannia metal , . , Tin, with antimony, copper, aud bismuth. ALLOYS. 503 Names. Combining Metals. Bronze Tin and copper, Gun-metal .... Tin and copper. Dutch gold .... Copper and zinc. Fusible metal .... Bismuth, lead, and tin, with, sometimes, cadmium. Gold with copper. . Gold with copper and silver. . Copper and zinc. . Copper and zinc. . Tin and lead. . Tin, with antimony, bismuth, and copper. . Copper and lead, with, sometimes, a little zinc. . Tin with antimony, bismuth, and copper. . Silicon and copper. . Lead, with a little arsenic. Silver and copper . Silver and brass. . Tin and lead. . Tin and copper. . Lead, antimony, and bismuth. . Copper and zinc. . Lead and antimony. . Copper and arsenic. Of the various kinds of brass the following are the most important : Finest Quality of Brass. Copper, 2 parts ; zinc, I part. Prince's Metal. Zinc, 2 parts ; copper, I part. Fine Malleable Brass, for sheets, tubing, &c., is made from various formulae. I. Copper, 7 parts ; zinc, 3 parts. II. Fine copper, 4 parts ; zinc, i part. III. Copper, 33 ; zinc, 25 parts. IV. Copper, 3 ; zinc, 2 parts. These alloys are malleable whilst hot. Red Brass contains only a small percentage of zinc, and sometimes as little as 8 or 10 per cent. Brass for Castings. The alloy for fine brass is sometimes used for castings, or either of the following are employed : I. Copper, 62 ; zinc, 35 ; lead, 2 parts ; tin, i part. . II. Copper, 60 ; zinc, 36 ; tin, 4 parts. These alloys are rather brittle and of a palish colour. III. Copper, 90 ; zinc, 7 ; tin, 2 parts ; lead, i part. Gilding Metal. I. Copper, 64 ; zinc, 32 ; lead, 3 parts ; tin, I part. II. Copper, 82 ; zinc, 18 ; tin, 3 parts ; lead, i part. Brass for Turning. I. Copper, 64 ; zinc, 33 ; lead, 2 parts. II. Fine brass, 98 ; lead, 2 parts, melted together. III. Copper, 61 ; zinc, 36 ; lead, 3 parts. Gold, Standard Old Standard Mosaic Gold . Ormoulu Pewter, common . best . ,' " Pot metal, Cock metal Queen's metal . Silicon bronze Shot metal . Silver, Standard . Solder, hard . soft Speculum metal Stereotype metal Tombac, Red tombac Type metal White Copper . 504 USEFUL INFORMATION. Brass Solder. I. Brass, 3 parts; zinc, I part. This is used for soldering tubes and joints, and for all purposes where great strength is required. II. Fine brass, 1 2 ; zinc, 6 parts ; tin, I part, melted together. Brass for Wire is made from copper 72, and zinc 28 parts; or copper 64, and zinc 34 parts. Button Brass, or Platin of the Birmingham manufacturers, is com- posed of 8 parts of brass and 5 parts of zinc, while their cheaper button metal is composed of copper, tin, zinc, and lead. Soldering. Hard Soldering. It not unfrequently happens, while scratch-brushing an article of jewellery or other small article, that some portion of the work will accidentally break away ; under such circum- stances it will be well if the gilder can himself repair the article instead of being compelled to return it to his customer or send it out to be repaired. With a view to furnish the operator with the means of doing repairs of this nature, the author introduces the following extract from his former work ; * and if the instructions herein given are carefully followed, the operator will have little difficulty in repairing accidental breakages. He should, however, first make himself master of the use of the blowpipe, and practise upon pieces of thin brass or copper wire before venturing to solder delicate articles of jewellery : " Hard soldering" consists in uniting any two metals, or parts of the same metal, by means of an alloy composed of two parts of silver to one part of brass. The silver and brass should be melted together as follows : Having obtained a broad piece of good charcoal, scoop out a slight hollow on the flattest surface to receive the alloy. Now place the metals in the hollow, and fuse them by means of a blowpipe, using either a jet of gas or an oil lamp with a good broad wick. As soon as the metals become hot, touch them with a crystal of borax (borate of soda), which will immediately fuse and act as a flux. The jet of flame must now be vigorously employed until the metals are completely fused. The fusion may be continued for a few moments in order to insure perfect amalgamation. When the "button" of solder is well melted, the flat surface of a hammer should be placed quickly upon it, by which means it will become flattened ; in this form it may be readily beaten out (unless a pair of steel rollers are at hand) until sufficiently thin to cut with a pair of jewellers' shears. The solder can be hammered out upon an anvil or any solid iron surface ; but as each time the blow is given the alloy becomes harder, it will be necessary from time to time to anneal it, i.e. place it again upon the charcoal and apply the blowpipe flame until the alloy is of a " cherry - red " heat ; it is then to be plunged into cold water, and is ready for * " Electro-metallurgy," by the Author 8th edition, p. 159. SOLDERING. 505 beating out or rolling as the case maybe, the object being to make the solder as thin as an ordinary card, or even thinner. When the operator is without a pair of rollers he must use the next best substitutes a hammer and patience. The solder before being used must be scraped with a keen steel edge, and then partly cut into thin strips, and these again cross-cut into small pieces or pellets about one-sixteenth of an inch square. These pellets may be cut when required for use, or kept in a clean box used for the purpose. The operator should next provide himself with a clean piece of slate, say about three inches square, and a small phial filled with water, and having a cork with a small groove cut in it from end to end. The bottle is used to apply moisture a drop at a time, whilst a large crystal of borax is rubbed upon the slate. By this means a thick creamy paste of borax is obtained upon the slate, which will be used as presently directed. The parts to be united or soldered must now be scraped clean wherever the solder is expected to adhere, and with a camel-hair brush or feather of a quill dipped in the borax paste brush over the parts to be soldered. A few pellets of the solder may be placed on the dry corner of the slate, and with the extreme point of the brush moistened by the paste one pellet at a time may be readily taken up and placed upon the prepared surface of the article. The article should be placed upon a flat piece of charcoal (made flat by rubbing on a flagstone), and, if necessary, tied to it by thin "binding wire." A gentle blast of the blowpipe will at first dry the borax, and the flame must then be increased (holding the blowpipe some distance from the flame in order to give a broad jet), and in a few moments, if the jet is favourable, the solder will " run," as it is termed, into every crevice, when the blowpipe must be instantly withdrawn. A very little practice will make the operator expert in this interesting art, and it will be advisable for him to practise upon articles of little value until he has not only acquired the use of the blowpipe, but also the proper kind of flame to make the solder run freely. After an article has been hard soldered it is allowed to cool, or may be at once placed in a weak solution of sulphuric acid (a few drops of acid to an ounce of water), which, after a few moments, will dissolve the borax flux which remains after the soldering is complete. The article should now be rinsed in water and dried. Soft Soldering. This consists in uniting articles made of sheet tin (tinned iron), lead, zinc, and sometimes iron, with an alloy of tin and lead. It is usually performed with a tool called a soldering-iron, which consists of an ingot or bar of copper, riveted to a cleft iron stem termi- nating in a wooden handle ; the operation may, however, in some cases be accomplished by means of the blowpipe flame. In soldering, the first thing to do is to well clean the parts to be united, which is most 506 USEFUL INFORMATION. conveniently done by scraping, a three-edged tool termed a scraper, or the edge of a penknife, being used for this purpose. In applying the solder to the two first-named metals, a little powdered resin is first sprinkled over the cleaned surfaces to be united ; the soldering-iron must be well tinned by first moderately heating it in a clear fire, then filing the bevelled surfaces of its point until bright and clean ; it must next be at once made to touch a lump of black resin, and then brought in contact with a strip of solder ; care should be taken that all sur- rounding parts of the point of the tool are well coated with solder. When about to apply the soldering-iron to the prepared surfaces, it must be first made moderately hot, not on any account red hot ; its point should then be wiped on a piece of cloth having a small piece of resin upon it, and then touched with the strip of solder, when a small globule of the metal will attach itself, and the tool may now be applied to the object to be soldered ; at the same time the strip of solder, being held in the other hand, should be brought in contact with the soldering-iron and a sufficient quantity of the solder allowed to melt while the tool is being applied. As the soldering-iron cools, it must be re-heated and cleaned as before. Sometimes powdered sal-ammoniac is employed in soft soldering, and it is a good plan to press the point of the hot tool upon a lump of this salt occasionally, by which the oxida- tion of its surface becomes removed. In passing the soldering-iron along the parts to be joined, the solder should run, as it is termed, freely and form a bright and even layer. In soldering iron with soft solder, the surfaces, after being well cleaned, must be brushed over with a solution of chloride of zinc, or " tinning salt ; " this is made by pouring a little muriatic acid upon a strip of clean zinc ; vigorous effervescence at once takes place, and when this has nearly subsided the solution is ready for use. The solu- tion may be applied to the cleaned iron surface by means of a camel- hair brush or the feather of a quill, when the soldering-iron is to be employed as before ; it should, however, be rather hotter for this pur- pose than for soldering the more fusible metals. In soldering zinc the tinning salt is also used, but a little muriatic acid spread over the surface is better, since it cleans the surface of the zinc, forming, of course, chloride in doing so. When it is desired to solder a wire upon a stout zinc plate for battery purposes, it is a good plan to moderately heat the end of the zinc to which the wire is to be attached, then to apply a few drops of the acid, and immediately apply the solder as before ; the end of the copper wire, being previously cleaned and tinned, is then to be put in its place, and the hot soldering-iron and sufficient solder applied until the end of the wire is imbedded in the material ; a cold hammer may then be pressed on the wire, which, by chilling the solder, will complete the operation. PLATINISING. 507 Sheet lead, such as is used for lining nickel and other tanks, should not be united by soldering, since the two metals, tin and lead, when in contact with the solution (especially a nickel salt) would slowly undergo chemical action, probably resulting in perforation of the lining. It is usual, therefore, to unite the sheet lead by the autogenous process, or " burning " as it is called, which consists in first scraping the surfaces clean, when a jet of hydrogen gas, or this gas mixed with common air, is applied, by which the two surfaces become fused together. This method of securing the joints of lead-lined tanks is now universally applied, and is unquestionably the best system that can be adopted. Soldering Liquid. As a substitute for the solution of chloride of zinc ordinarily used as a tinning salt, the following has been recom- mended : Make a neutral chloride of zinc by adding strips of the metal to muriatic acid, taking care to employ an excess of the former. Then add, while the liquid is still hot from the chemical action, as much powdered sal-ammoniac as the fluid will dissolve. Instead of using water to dilute the solution, use alcohol, keeping the liquid in a well-stoppered bottle until required for use. If crystals appear when the solution is placed in an open vessel for use, add a little alcohol, which will liquefy them again. To Remove Soft Solder from Gold and Silver Work. This may readily be effected by placing the soldered article in a hot solution of perchloride of iron, made by dissolving crocus or jewellers' rouge in muriatic acid and diluting the solution with four times its bulk of water, and there leaving it until the solder is removed. A formula recommended by Gee* for this purpose is composed of protosulphate of iron (green copperas), 2 ozs. ; nitrate of potassa (saltpetre), i oz. ; water, 10 ozs. Reduce the protosulphate of iron and nitrate of potassa to a fine powder, then add these ingredients to the water, and boil in a cast-iron saucepan for some time ; allow the liquid to cool, when crystals will be formed ; if any of the liquid should remain uncrystallised, pour it from the crystals, and again evaporate and crystallise. The crystallised salt should be dissolved in muriatic acid in the proportions of one ounce of the salt to eight of acid. Now take one ounce of this solution and add to it four ounces of boiling water in a pipkin, keeping up the heat as before. In a short time the most obstinate cases of soft solder will be cleanly and entirely overcome and the solder removed without the work changing colour. Platinising. This name is applied to coating thin silver foil with platinum, in the form of a black powder, whereby a vast number of fine points are produced, which facilitate the escape of hydrogen in * " The Goldsmith's Handbook," by George E. Gee, p. 144. 508 USEFUL INFORMATION. the Smee battery. This ingenious method of favouring the escape of hydrogen, instead of allowing it to accumulate on the surface of the battery plates, was suggested by Smee, and was the means of render- ing his admirable battery one of the most useful and popular voltaic batteries known. To platinise silver plates for the Smee battery, a solution is made by first adding to the necessary quantity of cold water one-tenth part, by measure, of sulphuric acid ; after mixing these by stirring with a glass rod, add crystals of chloride of platinum with stirring, until the liquid assumes a pale yellow colour; it is then ready for use. Several Smee cells are now to be connected in series, and a couple of platinum or carbon anodes, attached to the positive pole of the compound battery, suspended in the electrolysing cell. The sheet of silver foil to be platinised should have a copper wire soldered to its upper end, and be enclosed in a frame of wood ; it is then to be connected to the negative pole, and suspended between the pair of platinum or carbon plates ; all being now ready, the platinum solution is to be poured into the vessel until it reaches the upper surface of the silver foil. In about fifteen or twenty minutes, the silver will become coated with a deep black film of platinum in a finely divided state, when it may be withdrawn and rinsed, and is then ready for employment as the negative element of a Smee cell. To prevent the exciting fluid of the battery from attacking the solder which connects the wire to the silver, this, and a few inches of the connecting wire, should be coated with sealing-wax varnish. Steel-facing Copper Plates. A very good solution for coating copper plates with iron commonly termed steel- facing may be pre- pared by the battery process as follows : The depositing vessel to be used for coating the plates is to be nearly filled with water, in which is to be .dissolved sal-ammoniac, in the proportion of I part by weight of the latter to 10 parts by weight of the former, that is I Ib. of the salt to each gallon of water used to make up the bath. A stout plate of sheet iron, previously pickled, scoured, and rinsed, is to be connected to the positive electrode of a battery, and immersed in the solution ; a second plate of iron, about half the size of the former, and also rendered perfectly clean and bright, is to be connected to the negative pole of the battery, and suspended at a short distance from the anode, or larger plate. The battery is allowed to continue in action for two or three days, at the end of which time the iron cathode may be removed, and a strip of clean brass or copper suspended in its place, when, after a short immersion, this should become coated with a bright deposit of iron, provided that the solution has acquired a sufficient quantity of this metal during the electrolytic action. If such is not the case, the iron cathode must be again immersed, and the action kept up until a brass or copper plate promptly receives* a coating of ANTIDOTES AND REMEDIES. 509 iron . When the bath is found to deposit iron freely, the copper plate to be faced with iron is to be connected to the negative pole and im- mersed in the bath, where it is allowed to remain until sufficiently coated. A bright deposit of iron should appear upon the plate immediately after immersion, and the plate should become quickly coated all over if the bath is in proper condition and a suitable current employed. If, after the copper plate has been in the bath a short time, the edges assume a blackish appearance, it must be at once withdrawn, and well rinsed with clean water, and this is most effectually done by holding the plate under a running stream delivered from a flexible tube connected to a water tap. The plate must then be quickly dried, and afterwards washed over with spirit of turpentine ; it is then ready to be printed from. Antidotes and Remedies in Cases of Poisoning. Since some of the substances employed in electro-deposition are of a highly poisonous nature, and the mineral acids with which we have to deal (especially nitric and sulphuric acids) are exceedingly corrosive in their action upon the skin, as also are the caustic alkalies, soda and potash, a few hints as to the best antidotes or remedies to be applied in cases of emergency will, it is hoped, prove acceptable ; indeed, when we take into consideration the fatal promptitude with which hydrocyanic acid, cyanogen vapours, and cyanide of potassium will destroy life, it becomes the duty, not only of employers, but their foremen, to make themselves acquainted with such antidotes as can be applied at a moment's notice in cases of accidental poisoning or injury from cor- rosive substances. In the course of a long experience, the author has more than once narrowly escaped serious consequences, not only from accidental causes, but (in his youthful days) from careless disregard of the dangerous nature of cyanogen vapours. In the latter case his system was at one time so seriously affected by inhaling the vapours of cyanide baths as to partially reduce the power of the lower extre- mities. His esteemed friend, Mr. Lewis Thompson, a gifted scientific chemist and surgeon, having casually paid him a visit, upon observing the author's condition, and well knowing its cause, promptly pre- scribed six glasses of hot brandy and water. The advice was quickly followed, to the extent of half the prescribed dose, and by the fol- lowing day the symptoms had almost entirely disappeared. Upon another occasion, the author inadvertently swallowed a quantity of old gold solution, which he had placed in a small teacup for an experimental purpose, in mistake for some coffee without milk, which it was his custom to drink when at work in his laboratory. Having discovered his mistake he at once desired his assistant to get some luke- warm water without delay ; in his absence, however, he thrust his finger to the back of his throat, and by tickling the uvula, quickly 510 USEFUL INFORMATION. induced vomiting ; copious doses of warm water, assisted by again irritating the uvula, soon emptied the stomach, after which warm brandy and water completed the remedy, no ill effects from the accident being afterwards observable. Upon one other occasion, the author was ascending a spiral staircase leading to a plating room, when he suddenly felt a sensation of extreme giddiness ; promptly guessing the cause, he retreated as speedily as his trembling limbs would permit, and sought the open air, and as quickly as possible obtained a glass of brandy from the nearest tavern, which had the effect of checking the tremulous motion of the limbs and feeling of intense nervousness. The cause of the sensation above referred to was this : some old silver solutions had been treated with sulphuric acid, to precipitate the silver, a short time before, in an upper apart- ment, and the carbonic acid and cyanogen vapours liberated were descending to the base of the building at the time he ascended the staircase ; it was the remembrance of this fact that prompted him to retrace his steps as quickly as the shock to his system would allow. In mentioning the above incidents our chief object is to illustrate, from what has actually occurred, not only the sources of danger which callousness and inadvertence may invite, and to point out how such accidents may be avoided, but also to indicate how by promptitude more serious consequences may be averted. General Treatment in Cases of Poisoning. The first important step, in all cases of poisoning, is to empty the stomach with all possible dis- patch. This may generally be done (and should always be tried first) by thrusting the finger towards the throat, moving it about so as to tickle the parts until vomiting supervenes. While this remedy is being tried, a second person, if at hand, should hasten to procure some lukewarm water, which the sufferer should be made to swallow, whether vomiting has or has not occurred ; warm mustard and water may also be tried. If these remedies fail, the stomach-pump should be applied. The vomiting should be kept up and the stomach well washed out with some bland albuminous or mucilaginous liquid, as warm milk and water, eggs beaten up in milk or water, barley-water, flour and water, or any similar substances ready at hand. After the vomit- ing, a brisk purgative or enema may be administered, and nervous irritability or exhaustion alleviated by means of opium, ether, wine, or warm spirit and water, as the case may require ; only the " domestic remedies," however, should be applied, except under proper medical advice. Poisoning by Hydrocyanic Acid, Cyanogen, or Cyanides. When hydro- cyanic acid has been inhaled, the vapour of ammonia or chloride of lime should be at once applied, cautiously and moderately, to the nostrils ; indeed, this highly poisonous acid should never be used, ANTIDOTES AND REMEDIES. 511 especially by inexperienced persons, without the presence of a second person, holding an uncorked bottle of liquid ammonia or chloride of lime in moderate proximity to his nostrils. In case of poisoning by this acid, cold water should be at once poured upon the head, and allowed to run down the spine of the sufferer. In the case of hydro- cyanic acid or cyanides having been swallowed, four or five drops of liquid ammonia, in a large wine-glass full of water, may be admi- nistered. Mialhe recommends spreading dry chloride of lime upon a towel, folding it up in the form of a cravat, and moistening it with vinegar ; this is then placed over the mouth and nostrils of the patient, so that he may inhale the chlorine which is gradually liberated. In cases of poisoning by swallowing cyanides as gold and silver solu- tions, for example emptying the stomach by every means would undoubtedly be the most important step. The application of very cold water to the head and spine should not, however, be neglected in severe cases. As antidotes for cyanide poisoning, iron salts are recommended, which convert the deleterious acid into the comparatively innoxious prussian blue. Poisoning by Corrosive Acids. In case of either of the mineral acids nitric, sulphuric, or hydrochloric having been swallowed, copious doses of lukewarm water, mixed with magnesia, chalk, carbonate of soda, or potassa, should be administered at once. Milk, broth, salad oil, or oil of sweet almonds may also be given. Poisoning by Alkalies. Vegetable acids as vinegar and water, dilute acetic acid, lemon-juice should be given by preference, but if these are not at hand, very dilute hydrochloric, nitric, or sulphuric acid (about ten drops in half a pint of water) may be substituted. When the painful symptoms have subsided, a few spoonfuls of salad oil should be administered. Poisoning by Metallic Salts. The sufferer should be caused to drink tepid water copiously and repeatedly, vomiting being also urged by tickling the throat with the finger or a feather ; copious draughts of milk and the white of eggs (albumen) may also be given ; but flowers of sulphur or sulphuretted waters are recommended in preference, since these transform most of the metallic salts into insoluble sul- phides, which are comparatively inert. Cyanide Sores. These painful affections may arise from two prin- cipal causes : first, from dipping the hands or arms into cyanide baths to recover articles which have dropped into them a very common practice, and much to be condemned ; and second, from the accidental contact of the fingers or other parts of the hand, on which a recent cut or scratch has been inflicted, with cyanide solutions. In the former case, independent of the constitutional mischief which may arise from the absorption by the skin of the cyanide salts, the caustic 512 USEFUL INFORMATION. liquid acts very freely upon the delicate tissue of the skin, but more especially upon the parts under the finger nails. We have known instances in which purulent matter has formed under the nails of both hands from this cause, necessitating the use of the lancet and poultic- ing. Again, when cyanide solutions come in contact with recent wounds even very slight cuts or abrasions of the skin a troublesome and exceeding painful sore is sure to result, unless the part be at once soaked in warm water"; indeed, it is a very good plan, after rinsing the part in cold water, to give it a momentary dip in a weak acid pickle, then soak it for a few moments in warm water, and after wiping the part dry with a clean rag or towel, apply a drop of olive oil and cover up with a strip of thin sheet of gutta-percha. Poisoning by Acid Fumes. When the lungs have been affected by inhaling the fumes arising from dipping baths, stripping solutions, &c., or chlorine gas, the sufferer should at once seek the open air; he may also obtain relief by inhaling, in moderation, the vapour of ammonia from the stopper, not from the bottle itself ; or a little water may be put into a glass measure and a few drops of ammonia mixed with it, which may be inhaled more freely. When an apartment has become oppressive from the fumes of acid, it is a good plan to pour small quantities of liquid ammonia upon the floor in several places, but the acid fumes should be expelled as quickly as possible by the opening of all windows and doors. Caution. Never add an acid to any liquid containing cyanide, or f errocyanide, in a closed apartment, but always in the open air, taking care to keep to windward of the liberated gases, which are poisonous in the highest degree. APPENDIX. Electro-deposition of Platinum (Thorns 1 Process). This process, which has for some time past been carried out by the Platinum- plating Company, has for its object the " deposition of platinum with greater economy, solidity, and greater perfection than in the methods hitherto adopted," and the inventor claims, as an advantage over all other processes, that he obtains " a deposit which is so bright that it requires no subsequent polishing. This feature constitutes in itself an important advantage, as the cost of polishing is entirely abolished." In the preparation of his bath the inventor prepares a solution of chloride of platinum in the usual way, which is subsequently rendered neutral by any ordinary method. To this solution of platinum he adds a weak solution of common phosphate of soda, to which is next added a weak solution of phosphate of ammonia, and the whole are then boiled for several hours, during which operation a solution of chloride of sodium is added. The proportions of the above ingredients which it is preferable to use are as follows : Chloride of platinum, i ounce ; phosphate of soda, 20 ounces ; phosphate of ammonia, 4 ounces ; chloride of sodium, i ounce. The whole of the ingre- dients may be varied, but the proportions given have been found to produce good results. The solution may be worked at any suitable temperature, but it is preferable to work it above the ordinary tem- perature of the atmosphere. A strong current of electricity must be employed, and the cathode should be kept in motion while the deposition of the platinum is going on. The same bath may be used for a considerable time by adding fresh platinum solution and chloride of sodium solution as required, to keep up the original strength of the bath. When it is desired to coat surfaces to which platinum will not adhere directly, they must be first coated "in any suitable manner with a substance to which platinum will adhere. Electro -deposition of Aluminium and its Alloys (Burghardt and Twining* 's Process}. The inventors prepare a solution containing cyanides of aluminium and copper in the following way : A solution of chloride of copper is first formed by dissolving copper in nitro- hydrochloric acid arid afterwards expelling the acid by evaporating 5 14 APPENDIX. the solution to dryness, hydrochloric acid being added if necessary. Hydrated oxide of aluminium is next prepared by adding an excess of liquid ammonia to a solution of sulphate of aluminium, the precipitate being washed to free it from foreign salts ; this is then mixed with the chloride of copper solution. The mixture is then boiled and sufficient hydrochloric acid added to insure a perfect solution of the hydrated oxide of aluminium. The free hydro- chloric acid is next expelled by evaporation. In this way the in- ventors obtain what they term a double chloride of copper and aluminium. To prepare a bath containing, say, 24 ounces troy of metal, the ingredients would be compounded in about the following proportions : 20 ounces of metallic copper are converted into chloride as described ; 32 ounces of commercial sulphate of alumina are con- verted into hydrated oxide of aluminium, and the resulting products are then mixed, boiled, and freed from excess of hydrochloric acid by evaporation. " The resulting solution is now diluted with a suitable quantity of water and mixed with about 24 Ibs. troy of solid caustic soda dissolved in water, the mixture being gently heated for some time. The caustic soda precipitates out the copper as hydrated oxide of copper, and also the aluminium as hydrated oxide, which at once redissolve in the excess of caustic soda." [The patentees describe a method of determining whether the aluminium oxide has been com- pletely dissolved.] ' ' "We now add to the bulk of the solution, ' ' say the inventors, " about 16 ounces of solid cyanide of potassium (containing about 95 per cent, of potassium cyanide) to each ounce of metal in the solution, and heat the mixture until all the suspended hydrated oxide of copper is dissolved. We then add 8 ounces of solid bicarbonate of potassium to each ounce of metal present in the solution, and boil the solution continuously for about 24 hours, or as long as is found neces- sary, until the solution has cleared itself, after which it may be filtered if necessary. When it is wished to make the solution deposit the metal in a clear and bright condition, we add to the solution, whilst cold, about half a pint of a solution of hydrocyanic acid gas of the so-called ' Scheele's strength.' " If the solution, after being worked some time, becomes sluggish in its action, from excess of saline matter in the bath, an addition of cyanide is made, and the solution then boiled for some hours; but "if the solution already contains an excess of cyanide and carbonate of potassium which is apt to be the case when it has been at work for some time we consider that the addition of hydrocyanic acid gas solution, or the passing of hydrocyanic acid gas into the solution preferable to the addition of more cyanide. The action of the hydrocyanic acid consists principally in the formation of cyanide of potassium from the carbonate of potassium in the solution, it being a well-known fact that cyanide of potassium in the course of time WATTS' ZINC PBOCESS. 515 decomposes into carbonate." The solution above described " may be used in the plating of metal objects, or in the depositing of the alloy upon surfaces, for which purpose a dynamo -electric machine or battery of suitable power may be employed, a platinum or other suitable anode being used." The bath is worked at a temperature of about 180 Fahr. during the deposition ; but if it is wished to obtain a deposit of lighter colour, the bath is worked at a lower temperature. " When the object is to obtain the alloy as a precipitate," say the inventors, " we use the electric current to throw down the alloy without putting into the bath any object to receive the deposit or coating." Electrolytic Treatment of Zinc and its Ores (Watt's Process). This process, for which the author obtained a patent in April, 1887, has for its object the purification of crude or impure zinc, and the extrac- tion of metallic zinc from its ores, by electrolysis. To accomplish the first aim of this invention, namely, the production of pure zinc, a solution of a vegetable acid (preferably acetic acid) is first obtained, which is placed in a suitable tank. Slabs or thick plates of impure zinc are then suspended as anodes in the depositing vessel, and thin plates of good sheet zinc, sheet copper, iron, or other suitable metal, are used as cathodes or receiving plates, the surfaces of which may have a coating of plumbago, or be slightly greased to prevent the adhesion of the deposited metal. When the required series of anodes and cathodes have been suspended in the acid solution, the current of electricity is allowed to pass, and in a short time the acid solution becomes impregnated with zinc, and the metal deposits in a state of great purity upon the receiving plates, in the form of a bluish white film : at the same time the impure zinc anodes gradually assume a discoloured or even blackish appearance, due to the metallic impuri- ties with which impure zinc is more or less contaminated, forming an insoluble film on their surfaces. This film increases in thickness as the operation progresses, and the insoluble matters eventually become dislodged, and fall from the anodes in flakes or masses to the bottom of the tank ; or they may be removed mechanically by occasionally scouring the plates with a hard brush. During the electro -chemical action, and until the acid solution becomes well charged with zinc, a good deal of gas is liberated at the surface of the plates, to check or moderate which carbonate or oxide of zinc may be introduced in small quantities at a time, until the evolution of gas nearly OP almost entirely ceases, when the deposition proceeds more favourably. The solution, however, improves by continual Working, and the deposit becomes more uniform than when the bath is newly prepared. When the receiving plates have become sufficiently coated with the purified zinc, they are removed from the baths and replaced by fresh plates, and the zinc -coated plates are then well rinsed and dried. If 516 APPENDIX. the receiving plates are of pure, or nearly pure, zinc, they may be at once melted and cast into ingots in the usual way ; but if copper or other metal be employed for the cathodes the deposited zinc must be stripped off with the aid of suitable tools, and the zinc then col- lected for melting. Instead of employing a solution of a vegetable acid direct as the electrolyte, a solution of zinc in a vegetable acid may be employed, preferably acetate of zinc, which is found to be most effectual. This may be prepared by digesting the carbonate or oxide of zinc, or clean scrap zinc, in acetic acid, with the aid of such agitation as may be necessary to hasten the solution of the zinc. The solution is then allowed to settle, and the clear liquor is afterwards drawn off as required, and is by preference employed in a moderately diluted condition. In refining impure zinc with the solutions prepared by either of the fore- going methods, the insoluble metallic impurities, which are liberated at the anodes, eventually form a black slime, or mud, at the bottom of the tank, and from which the several foreign metals may be recovered by ordinary processes. The refined zinc is specially ser- viceable for voltaic batteries, since, from its extreme purity, the "local action" which occurs even with the best commercial zinc, from the presence of negative metals, is reduced to a minimum, if not absolutely avoided. Pure zinc is also available for alloying with pure electrolytic copper, to form brass of a high quality for various pur- poses in the arts, but more especially for cartridge cases, 'the metal for which is required to be absolutely free from lead to prevent the cart- ridge from " jamming," as it is termed. In treating zinc ores for the extraction of the zinc by this process, the ore (if it be calamine, or native carbonate of zinc) is first finely ground and sifted, and then introduced, in small quantities at a time, into a strong solution of a vegetable acid, say commercial acetic acid, containing about 15 or 20 per cent, of real acid. The operation is as- sisted by agitation, and the powdered ore introduced gradually in order to allow the liberated carbonic acid to escape without causing the con- tents of the tank to overflow. The supply of powdered ore is kept up until the required quantity (which may be approximately estimated by previous calculation) has been introduced. The contents of the tank will then be subjected to continuous agitation until the liquor has become neutral, or nearly so, which can be ascertained by testing with litmus paper. When the solution is found to be sufficiently neutral for the electrolytic bath (a slight excess of acid not being objectionable) the contents of the tank must be allowed to settle, and the clear liquor is afterwards drawn or pumped off for the extraction of the zinc, in the manner above described. The anodes may be of carbon or platinum, or other metal insoluble in the acid, but flat plates of carbon ELECTRO-DEPOSITION OF COBALT. 517 answer very well for the purpose. For the cathodes plates of thin sheet zinc of good quality may be used ; otherwise copper or iron, slightly greased to prevent the adhesion of the deposited metal, may be employed. The acetate of zinc solution (more or less impure) maybe used in its concentrated condition, that is, as it comes from the dissolving tank, or it may be moderately diluted with water ; but it is found that a liquor which has a specific gravity of about 1,150 to 1, 1 60 (water being 1,000), yields very good results as an electrolyte for the extraction of the metal. As the metal becomes deposited upon the receiving plates, an equivalent proportion of acid is set free in the liquor, and in order to prevent an accumulation of this free acid in the electrolyte, and to keep up the normal metallic strength of the solution as far as possible, and also to prevent polarisation, which an excess of free acid would tend to set up, it is necessary that a continuous supply of fresh neutral, or nearly neutral, zinc solution should constantly enter the baths, and also that a corresponding proportion of the exhausted acid liquor should be removed from the baths during the entire period when the electrolytic reduction of the zinc is going on. To accomplish this, a system of circulation must be adopted, which may be effected by any well-known method applied in similar processes. The exhausted Liquor from the electrolytic tanks is conveyed into a suitable vessel or tank, and is there re -saturated with zinc from the ore, in the manner before described. In treating blende, or " black jack" (native sul- phide of zinc), by this process, the ore is first roasted in the usual way, to expel the sulphur, and the roasted ore is afterwards pulverised and sifted. The finely powdered ore is then digested in a solution of a vegetable acid (acetic acid by preference) as before. When the solu- tions of zinc are found to contain any considerable proportion of lead, iron, &c., these may be precipitated as sulphides, by passing a stream of sulphuretted hydrogen through the liquors while in an acid condition. Electro -deposition of Cobalt. In the autumn of 1887 the author, believing that cobalt, as an attractive and serviceable coating for other metals but more especially for articles of brass, copper and steel deserved more attention than had hitherto been accorded to it by electro-depositors, pursued a long series of experiments with a view to ascertain the behaviour of certain salts of cobalt under the action of the electric current, hoping that the results obtained* would not only be instructive to the student of electro-chemistry, but also in some degree useful to those who pursue the art of electro -deposition as a business. It had often struck the writer as being somewhat remarkable that cobalt should have received so little attention from # Vide Electrical Review, Nov. i8th and 25th, and Dec. and, 1887, 5 1 8 APPENDIX. those who are engaged in depositing metals upon each other for the various purposes of art, since it is not only whiter than nickel, when deposited under favourable conditions, but it also requires but a very feeble current for its deposition as compared with that required by the former metal. It is true that cobalt is a dearer metal than nickel, but since a cobalt bath requires only about one-third of the quantity of "salts" required to make up a nickel bath, the actual cost of the electrolyte in each case would be about the same. The- price of cobalt anodes is also higher than the corresponding plates of nickel, but when we consider the small quantity of metal that is usually required to be deposited upon ordinary work, the relative cost of the respective metals need scarcely be seriously considered. In the series of papers referred to the author endeavoured to show that the adoption of cobalt-plating, or cobalting, would probably be accepted by the public as a novelty, and thus give a fillip to the electro -plating industry, but more especially to that branch of it which is devoted to coating metal work with nickel. On making inquiries as to the probable reason why cobalt -plating had been so little adopted, it soon became apparent that the subject had hitherto been treated chiefly in an experimental way, and that the information furnished by writers on the subject was scarcely sufficient to guide those who were willing to turn their attention to the deposition of this metal as a new industry. Moreover the difficulty of obtaining anodes of cobalt, iand reliable cobalt salts, also militated against the adoption of cobalt-plating for practical purposes. Since both these necessaries can readily be obtained from Messrs. Henry Wiggin and Co., of Birmingham, at the present time, there is no practical obstacle in the way of those who may feel disposed to try their hands at cobalting as an addition to their present routine of operations. Of the many cobalt solutions which the writer tried, the following were found to be the most effective and reliable, namely, the sulphate of cobalt, the double sulphate of cobalt and ammonia, the chloride, the double chlorides of cobalt and ammonium, and the chlorides of cobalt and sodium. These salts were employed in the proportions, and with the results, given below. Sulphate of Cobalt. In each gallon of water required to make up a bath, 5 ounces of crystals of sulphate of cobalt are to be dissolved, which is most conveniently done by dissolving the crystals in suffi- cient hot water, and finally adding cold water to make up the neces- sary quantity of solution. The bath should be allowed to rest until cold, and be worked with rolled or cast cobalt anodes, either of which may be obtained from the firm above named. The current density should not exceed 2 to 4 amperes per square foot of cathode surface, and the articles to be coated (if required to be bright) should be pre- ELECTRO-DEPOSITION OF COBALT. 519 viously well polished, potashed, and scoured, as for nickel-plating, be- fore being put into the bath. As in the case of nickeling, it is also absolutely necessary that the most scrupulous cleanliness be observed, since carelessness in this respect might cause the work to strip at such parts as may have been badly prepared. Brass, copper, and steel are readily cobalted in this bath. Double Sulphate of Cobalt and Ammonium. To prepare a bath from this salt, 5 ounces of the crystals are dissolved in each gallon of water, and the current should be of about the same density as before ; it may, however, be somewhat diminished when coating steel articles. After a time, articles coated in this bath assume a rather dull appearance, but since electrolytic cobalt is somewhat softer than nickel, the dull burr may readily be rendered bright by scratch - brushing, an operation which would have but little effect on a corre- sponding surface of nickel. If carefully worked, this solution should yield very good results, and may be considered a good practical bath. It must, however, be used with a feeble current, otherwise the metal will deposit too rapidly and consequently be liable to strip off before a sufficiently stout film is obtained. In cobalting with this solution, and indeed with most of them, it is absolutely necessary that the deposit should progress slowly at first; if the film has " struck" a few seconds after immersion, that is all that is needed to ensure adhe- sion, and the current may be gradually, but moderately, increased after a few minutes. In other words, if the deposit be allowed to jump on, it will most assuredly jump off when the film thickens. Chloride of Cobalt. A bath may be prepared from this salt by dis- solving about 5 ounces, or even less, of the crystals in each gallon of water. With a very feeble current brass and copper readily receive a fine white and bright film of cobalt, which, however, becomes dull after a time. If worked with care, keeping the current low, very good deposits may be obtained from this solution. Chlorides of Cobalt and Ammonium. In making up a bath from this double salt, from 4 to 5 ounces of chloride of cobalt crystals are dis- solved in each gallon of water, and to the solution is added about 3 ounces of sal-ammoniac, the whole being stirred until the latter is dissolved. This bath must be worked with a still more feeble current than the last, otherwise the deposited metal will be liable to strip from the articles coated. The deposit from this solution is very bright, and of a fine white colour. Chlorides of Cobalt and Sodium. To a solution of chloride of cobalt, containing 5 ounces of the salt per gallon of water, 3 ounces of common salt are added and dissolved. With a weak current, articles of brass or copper promptly become coated in this bath, the deposit generally remaining bright for a longer period than in either of the previous 520 APPENDIX. solutions. The anodes keep very bright and clean in working this bath. Double Sulphates of Cobalt and Ammonium, with Chloride of Sodium added. Well knowing, from his own experience, and that of others, the great advantages which are derived from the addition of common salt to nickel baths prepared from the double sulphates of nickel and ammonium, by which net only is the conductivity of the solution greatly increased, but the character of the deposited metal materially improved, the author determined to ascertain whether similar advan- tages could be obtained by adding common salt to a bath prepared from the double sulphates of cobalt and ammonium. For this purpose a solution was formed by dissolving crystals of the double salts, in the proportion of about 5 ounces to the gallon of water. About 5 per cent, of common salt was then added and dissolved in the liquor, and a clean brass cathode immersed and allowed to remain until fairly coated. The addition of the salt, however, did not present any apparent advan- tage ; an additional 5 per cent, was therefore given, after which the deposit a feeble current being used became more prompt, and a satisfactory film of cobalt was obtained in about half an hour. A third portion of salt making 15 per cent, in all was next added, and a fresh plate immersed, which received a white but somewhat dull film of cobalt, but, however, very uniform in character. Although the de- posits obtained in the salted solution were much less bright than those from the plain solution of the double sulphates, it may be mentioned that the dull bloom, which had a pearly hue, was readily brightened by the scratch-brush or by scouring with moist silver sand. It would therefore be easily rendered bright by the ordinary process of polish- ing. When comparing the results obtained from nickel solutions to which common salt has been added, with those in which the saline material has been added to cobalt solutions, it became evident that the advantages derived from the addition of salt were more marked in the case of nickel baths. In depositing cobalt from its solutions, although it is necessary, in order to obtain a firmly adherent film, to employ weak currents of electricity, the colour of the deposit is never.so good that is, the film never acquires its full degree of whiteness when the current is below a density that will yield a prompt deposit ; that is to say, the article to be coated should become covered with metal almost immediately after immersion. Professor Silvanus Thompson's Cobalt Process. This process, for which Professor Thompson obtained a patent in 1887, has for its object ''the deposition of cobalt in films of greater tenacity, density, and brilliance of tint, than have heretofore been obtainable with certainty. The solution for depositing cobalt may consist of sulphate or chloride of REMOVING TIN FROM TINNED IRON. 52! cobalt, or of the double sulphate or chloride of magnesium, or other suitable soluble salt of magnesium, or a mixed soluble salt of magne- sium and ammonium may be added to the solution of cobalt salts. The citrate of magnesium is a useful salt, and it may be formed in the solution by adding citric acid and magnesia, or carbonate of mag- nesium, to the solution, citrate of ammonium, or simply citric acid may be added te the solution." As an example of one way of carrying out the invention, a bath may be prepared by adding to 10 pounds of pure water* I pound of the double sulphate of cobalt and ammonium, ^ pound of sulphate of magnesium, ^ pound sulphate of ammonium, i ounce of citric acid, and 2 ounces of carbonate of ammonium. The solution may be used warm or cold, but if heated to at least 35 C. (95 Fahr.) gives a brilliant deposit with greater readiness than when used cold. Another method of carrying out the' invention is as follows : Half -a -pound of sulphate of cobalt is dissolved in 4 pounds of pure water ; 5 pound of sulphate of magnesium is dissolved in 4 pounds of water ; these solutions are mixed, and water added to make up I gallon. A quantity of sulphate of ammonium, not exceeding pound, may with advantage be added. In carrying out this process, the author states that good deposits of cobalt are obtained, when either of the above solutions is diluted with an equal bulk of water, but in that case a stronger current in proportion to the surface of deposition must be employed. " The best current density," says the inventor, " I find to be not less than I ampere, nor more than 4 am- peres per square foot of depositing surface, but a somewhat stronger current may be advantageously employed during the first few minutes of deposition, so as to secure a rapid striking film on the surface, the current density being diminished so soon as the surface is once covered with a film." The work to be coated by this process must be scrupulously clean, and otherwise prepared in the same manner as for nickel-plating. Removing Tin from Tinned Iron. The recovery of the tin from tin scrap, preserved fruit and meat tins and other waste of a similar character, has long occupied the attention of experimentalists, both at home and abroad, and several ingenious processes have been devised and patented, and, we believe, carried out with some success. When experimenting upon this subject a few years since, the author tried, amongst other solvents, perchloride of iron a material which, for another purpose, he had prepared in very large quantities, and was therefore well acquainted with the most economical method of prepar- * By pure water, the inventor explains, is meant simply newly-boiled and filtered water, or preferably distilled water, 522 APPENDIX. ing it. In stripping tin from tinned iron scrap with the perchloride of iron, the solution of the salt was employed hot, and the scrap then introduced and kept constantly in motion until the whole of the tin was dissolved from the surface of the fragments, which was generally effected in a few minutes. After a time the characteristic orange - yellow colour of the perchloride disappeared, leaving a green solution of protochloride of iron, in combination with the corresponding salt of tin. It was now found necessary to again peroxidise the iron solu- tion, which was effected by trying various ordinary agents in succes- sion, nitric acid being found to answer the purpose readily. Since the perchloride of iron as a de-tinning agent has somewhat recently formed, in part, the subject of a patent, it will be well to give the inventor's description of his method of applying it. The process referred to, which is given below, does not, however, depend exclu- sively upon the employment of perchloride of iron, as will be seen from the abridged details given. Garcia' s Process. This process, for which a patent was granted in 1886, consists more especially of "an improved method of treating cuttings, or waste, of tin plate in order to remove the metallic tin, but is also applicable to the separation of tin combined with metals, such as copper, zinc, or lead, or in combination with oxygen. The process consists first in making solutions of tin, preferably protochloride of tin, slightly acid, and afterwards extracting the tin in a metallic state by means of the simple apparatus used in the ordinary process of electro - typing." This consists in applying the " single cell " arrangement, as it is called, in which a plate of zinc is immersed in a porous cell filled with a saline solution, or acidulated water, and which is placed in a larger vessel containing a solution of tin in lieu of the sulphate of copper, as in electrotyping. The zinc plate is connected by a suitable conducting wire to sheets of tin plate, placed round the porous cell, upon which plates the tin becomes deposited. " Supposing," says the inventor, " cuttings of fresh tin plate are to be used, as often happens, I place them in vessels of material unaffected by the chemical agents employed, and keep them in movement by any convenient mechanical means, so as to prevent them from adhering together, since if left at ifest they would remain adherent, and to a great extent escape the action of the acid liquids. These acid liquids may vary according to the character of the tin cuttings, or fragments, but I prefer to use a mixture of hydrochloric and nitric acids, in about the following pro- portions, namely, 250 to 300 kilogrammes of hydrochloric acid, and 8 to 12 kilos, or even less, nitric acid." The vessels employed for this purpose may be constructed of stoneware, glass, slate, &c., and the mixed acids diluted with about 1,000 litres of water, the acid liquor being heated by steam passing through coils, or otherwise, to the REMOVING TIN FROM TINNED IRON. 523 temperature of about 80 to 100 degrees. [Centigrade ?] "While the process of solution is going on a certain proportion of iron is also dis- solved in removing the last particles of tin, the fragments being removed when the further solution would cease to be economical." It is stated that the foregoing proportions of acids and water are sufficient to effect the separation of the tin from one ton of tin scrap, as, for example, preserved food cans. "Instead of nitric acid," says the patentee, " perchloride of iron may be used, by which the tin is effectually separated. The perchloride is preferably produced by dis- solving 80 to 90 kilogrammes of peroxide of iron in 300 to 350 kilos of hydrochloric acid, this quantity being sufficient to separate the tin from a ton of tin plate, the quantity of water being the same as before, so as to completely cover the metal from which the tin is to be re- moved." The patentee next states that " the use of perchloride is new for the purpose and in the manner described, and forms an important part of the invention." As to the novelty of perchloride of iron being applied as a "stripping" solution for tin, we can scarcely agree to this, since this salt has long been used for the purpose by jewellers and others in common practice, and indeed has been recommended by various writers as a useful solvent not only of tin, but also of lead and copper. Montague's Processes. The first of these two processes both of which are protected by patent consists of a method and apparatus for separating tin from tinned sheet metal, such as empty tin boxes, tin scrap, &c. "Broadly speaking," says the inventor, "the method consists in conveying hydrochloric acid gas into a closed vessel con- taining the material the separation of the tin from which it is desired to obtain. After the closed vessel containing the tinned sheet metal has become completely saturated [charged?] with hydrochloric acid gas, whereby the latter combines with the tin, a shower of water is allowed to fall over the sheet metal, and instantaneously the said gas is converted into liquid protochloride of tin ; the tin, entirely re- moved from the sheet metal, is dissolved in the protochloride of tin." The solution of tin is afterwards drawn off from the closed vessel and the metal precipitated either by means of zinc, " lime wash," or other- wise. It is obvious, however, that the metal would be more economi- cally recovered by electrolysis. In the accompanying drawing, A is a retort into which is placed a charge of sulphuric acid and chloride of sodium for producing, with the application of heat, hydrochloric acid gas in the usual manner. The gas is conveyed by a pipe, B', into a closed vessel, B, containing a charge of tinned sheet metal scrap or cuttings, the latter material being heated to a temperature of 150 to 1 60 Fahr. by a jet of steam supplied by a generator, D', and pipe, D. After the tinned sheet metal cuttings, or scrap, have become saturated 5 2 4 APPENDIX. with hydrochloric acid gas, a shower of water, supplied by a pump, F, and a pipe, c, is conveyed into the closed vessel, B, by a perforated pipe, E, so as to completely wash over the tinned metal scrap. The solution thus produced is protochloride of tin, which is drawn off into a pan, H, by a tap, a. The tin, precipitated by zinc or otherwise, is placed under a press, M, to remove the liquid attached to it, and is afterwards melted in a crucible, P, and cast into ingots. By a second patent, dated May 2nd, 1887, M. Montagne introduces an improvement on the foregoing process, which may be thus briefly described : The tinned scrap is placed in a series of brickwork cham- Fig. 145- bers lined with any suitable material capable of resisting the action of acids, and sufficiently thick to retain heat for a long time. These chambers are put into communication by a system of piping, provided with suitable valves capable of allowing the acid gas to pass succes- sively into several chambers before passing to the exit or chimney, completely exhausted by its passage through material less and less attacked by aid. Let it be supposed for the sake of clearness, " says the inventor, "that three chambers are employed, and that the gas passes successively through chambers i, 2, and 3. The gas first ELECTROLYSIS OF LEAD SALTS. 52^ reaches chamber I (through a pipe and valve) , in which the extraction [dissolving of the tin] will be soonest completed. When the extraction has been effected, chamber 1 is completely shut off by closing the valve of the gas supply pipe, and the valve which puts chamber i in com- munication with chamber 2 is opened. The acid gas will then first enter chamber 2 by its valve and be led into chamber 3, and t&enoe to the chimney. While chamber I is shut off a spray of water is allowed to fall into the same from a perforated coil or otherwise. At the same time, in order to reach the parts which are least accessible, a jet of steam is supplied from a generator by pipes, the same being cooled by the spray of water, and forming vapour which settles on all the surfaces covered with protochloride of tin, and carries it off in solution. The condensation of all the hydrochloric acid gas is thus certain to be effected, and chamber I can be opened for removing the metal deprived of its tin, and recharging the same with a fresh batch of tinned scrap without being inconvenienced by the acid vapours. When this is done the chamber is closed, and placed again in circuit by opening the valve, and thus making this chamber the last in the series ; that is to say the gas entering through chamber 2 passes into chamber 3, and then into chamber I, whence, it escapes through the chimney. The order of circulation thus becomes reversed, as will be readily seen, and it is obvious that the number of chambers may be varied at will. To recover the tin from the solutions thus obtained, the inventor employs zinc or iron, or otherwise lime ; but the electrolytic method would doubtless be more economical. Electrolysis of Lead Salts. Having made a long series of experi- ments in the deposition of lead from the solutions of its various salts,* the author is enabled to give the details of a few results which may possibly be useful to the practical operator. Of the numerous lead salts from which solutions were prepared for the purposes of his experiments, the following were found to yield the most .satisfactory results : the tartrate of lead ; the same prepared by electrolysis, and phosphate of lead dissolved in caustic potassa. The tartrate of lead bath was prepared by digesting recently-precipitated, and moist, hydrated protoxide of lead in a strong and hot solution of tartaric acid, in which the oxide dissolved very freely. The solution was then allowed to cool and the clear liquor afterwards poured off and moderately diluted with water. With the current from two small Daniell cells, in series, and a sheet lead anode, a brass plate received a prompt and bright deposit of lead, of good colour, and it was noticed that no hydrogen was given off at the cathode. The film of deposited metal continued bright for a considerable time, and maintained a * Vide Electrical Review, April 6th, i3th, and 27th, 1888. 526 APPENDIX. perfectly uniform and reguline character, while being also firmly ad- herent. It was also observed that the lead anode, which kept clean and bright, had been freely acted upon during the electrolytic action. In this solution, brass, copper, and steel were rapidly coated with lead, which firmly adhered to the respective metals. In order to determine whether the solvent action of tartaric acid, under the influ- ence of the current, was sufficient to maintain the tartrate bath in an uniform condition, the following method was tried. A strong solution of tartaric acid was first prepared, in which was placed a sheet lead anode and a brass cathode, the current from two Daniells, as before, being used. Shortly after the respective electrodes had been immersed, hydrogen bubbles appeared all over the surface of the negative plate, from which they had little disposition to remove until the plate was briskly shaken in the bath. In about half an hour a bright film of lead formed upon the negative plate, at which period it was observed that the hydrogen bubbles ceased to be evolved at its surface. Since only one -half of the brass plate had been immersed in the acid liquor up to this period, the remaining portion of the plate was now lowered into the bath to ascertain whether the hydrogen would again show upon the brass surface only, and not upon the lead-coated half of the plate, and such actually proved to be the case, for while the brass surface instantly became covered with gas bubbles, the lead coat- ing was entirely free from them. It thus became evident that when forming a lead bath by electrolysis, from a solution of tartaric acid, that both electrodes should be of lead, or that the negative plate should first be coated with a film of that metal. Having thus determined the solubility of lead in the tartaric acid, under the influence of the cur- rent, it became still more apparent that the tartrate of lead could be employed with advantage in the preparation of a lead-depositing bath, and there is little doubt that a solution of this salt, of moderate strength, if worked with a feeble current, is very suitable for the electro -deposition of this metal. It was noticed, however, that the deposited metal had no disposition to assume the crystalline or spongy form in the foregoing solutions, which is too commonly the case with most solutions of lead salts. Phosphate of Lead in Caustic Potassa. A bath was prepared from this combination as follows : A quantity of chloride of lead was first obtained by adding a strong solution of common salt to one of nitrate of lead, the resulting precipitate being afterwards well washed with cold water. The precipitate was next dissolved in boiling water, and to this solution was added cautiously, so as to avoid excess as recom- mended by Mitscherlich, to prevent the formation of a subphosphate a hot solution of phosphate of soda. The white precipitate of phos- phate of lead thus formed was next washed repeatedly with cold water, ELECTROLYSIS OF LEAD SALTS. 527 and a strong solution of caustic potash then gradually introduced until the phosphate was entirely dissolved. The concentrated solution was next diluted with about eight volumes of water, and electrolysed with the current from a single small Daniell cell, when on immers- ing a clean brass plate as a cathode, this at once became coated with a bright film of lead, but after a few seconds' immersion the deposit assumed a dull appearance, while there was a copious evolution of hydrogen at the negative plate. To check this, the liquid was still further diluted by the addition of nearly an equal bulk of water, after which the subsequent deposits retained their brightness for a long period, while the anode exhibited a perfectly clean surface. The metal deposited from this bath adhered very firmly to the cathode, and there was very little disposition to sponginess a very common characteristic of electro -deposited lead. Peroxide of Lead Colourations. When electrolysing the various salts of lead, the writer frequently repeated experiments obtained with lead anodes by substituting platinum, steel, or a polished nickel-plated sur- face, with a view to observe the variations of colour which the peroxide of lead might assume when formed upon the positive electrode under certain conditions of the electrolyte. Since some of the results ob- tained were exceedingly beautiful, and might be susceptible of prac- tical application for ornamental purposes, a few details obtained may probably prove interesting. In electrolysing a solution of the basic nitrite of lead with a platinum anode (3 Daniell cells in series being used), a yellow deposit of peroxide was first formed upon its surface, which was quickly followed by superb iridescence on both sides of the plate. After about a minute, two rainbow bands appeared on the upper part of the anode, the remaining surface assuming a deep crim- son colour, changing to a purple. In a solution of sulphate of lead in caustic potash, platinum and steel anodes received a golden yellow film, which, even after a long immersion, did not undergo further change. In a solution of lactate of lead a platinum anode at first received a golden yellow film, succeeded by a steel grey at the lower part of the plate ; in a few seconds a deep orange colour began to appear at the lower corners, followed by the primary colours in succession, which rapidly blended as in the prism, producing a remarkably fine effect, which could be modified at will by increasing or diminishing the cathode surface. In a solution of sulphocyanide of lead a platinum anode received a rich golden yellow film, which did not undergo further change of colour. Similar results were obtained from solutions of pyrophosphate of lead, and salicylate of lead. In a moderately strong solution of nitrate of lead a very brilliant iridescent film was obtained upon a platinum surface instantaneously ; when this solution was considerably diluted with water, and a small cathode surface say 528 APPENDIX'. about three square inches immersed, the effects were still more striking, though developing more gradually. In a solution of ben- zoate of lead, -a pale yellow colour was first obtained, succeeded by orange, then deep orange, with a slight tendency to iridescence. When the film was rubbed with the finger, while still wet, the pris- matic colours at once became visible. Crystalline Deposits of Lead. When electrolysing the various salts of lead, the author frequently met with crystalline deposits of the metal of remarkable beauty, which he was desirous of preserving if practicable. Having found that such metallic crystals could be most satisfactorily obtained for this purpose upon flat surfaces, and when formed upon a transparent material, as glass for example, that im- pressions of the crystals could be obtained by the ordinary process of photographic printing, he will now briefly explain the method adopted, which it is hoped may prove not only interesting but, possibly, useful. In producing crystals of lead upon plane surfaces, solutions of the acetate or nitrate of lead may be employed, and the crystal- line forms may, to some extent, be varied by employing solutions of various strength, and also by increasing or diminishing (within certain limits) the density of the current. If we take a solution of the acetate of lead, for example, the bath may be a half -saturated solution of the salt, rendered slightly acid by the addition of a few drops of acetic acid. A plate of glass (say about 4^ X 6 inches) is then to be laid in a flat dish, and a lead anode a strip of sheet lead about 2X3 inches connected to the positive electrode of a 2 -cell Daniell battery, is allowed to rest on one end of th'e plate, and a strip of sheet brass, attached to the negative pole, is to be placed on the glass at the op- posite end. The solution of lead salt is next to be carefully poured into the dish until the glass plate is completely immersed. In a few moments crystals of lead will form upon the brass plate, and extend forward (and also backward to some extent) and gradually spread over the surface of the plate until the anode is nearly reached, when this latter electrode should be removed. The brass cathode must now be held firmly and steadily between the fingers, and the crystals attached to it gently removed with the blade of a penknife or thin strip of wood, but great care must be taken not to shift the position of the main group of crystals, which a little awkwardness would readily do. When the cathode is detached the glass plate should be gently raised at one end, which may be conveniently done with the forefinger and thumb of both hands, and the liquid allowed to flow from its surface very gradually, otherwise the crystalline film will slide off the plate ; with ordinary care, however, this need never occur. The plate bear- ing the crystals may next be laid on a pad of blotting paper, sup- ported at one end by a piece of wood, so as to allow the liquid to freely ELECTROLYSIS OF LEAD SALTS. 529 drain from the crystals. The fingers of the operator should be well rinsed after dipping in the lead solution. The solution is next to be poured out of the dish, and the vessel well rinsed, after which the glass plate is to be again laid in the dish, and water gradually and slowly poured in until the crystals are well covered, the object being to wash away all the lead solution that surrounds them. In doing this, however, much care is needed to avoid disturbing or shifting the crystals. It may here be remarked that since water produces a white precipitate in solutions of acetate of lead (unless veiy acid), it is necessary to remove the plate of crystals before the white precipitate has time to settle. The glass plate therefore should be removed, as before, almost immediately after the water has covered the plate, the liquid then thrown away, and the washing operation resumed, the process being repeated several times to remove all traces of the lead salt, otherwise the salt will re-act upon the delicate crystal film during the subsequent drying, causing it to become dull and brittle. When well washed the crystals should be perfectly bright and metallic. After the final washing the plate should be well drained upon blot- ting paper, after which it may be held before a clear fire until the crystals are perfectly dry. When the plate has afterwards cooled, so as to feel merely warm when touched with the back of the hand, a thin chloroform varnish (such as is used by photographers) should be .poured on the plate, and allowed to flow all over, the surplus being conducted to the varnish bottle by tilting the plate. The plate should then be again gently wanned to prevent the varnish from chilling. A photographic print of the crystals is obtained by treating the plate of crystals precisely in the same way as a photographic negative. The plate being la ; d in a suitable printing frame, crystals upward, a piece of albumen: sed paper, sensitised in the usual way, is laid upon it, and above this several folds of blotting-paper. The jointed back of the printing frame is then laid over all, and the springs of the frame adjusted as usual. To obtain a perfect impression, or print, of the crystals, the glass of the frame must be exposed to strong sunlight for at least half an hour, and it is probable that even double that time may be necessary to secure all the finer details of some of the more fibrous crystals. When the printing is complete, the photographic print is removed, and fixed and toned in a solution of hyposulphite of soda, to which a small quantity of chloride of gold has been added in the usual way, and it is afterwards to be well washed and dried, when it may be trimmed and mounted on a suitable card. The accompanying engrav- ings from the Electrical Review are reproductions of three photographs obtained in the manner described. Fig. 146 is from a photo of crystals produced with a solution of nitrate of lead, and Figs. 147 and 148 respectively represent those produced from a solution of the acetate of MM 530 APPENDIX. lead. It should be mentioned that in producing crystals of lead upon plates of glass to be printed from, from solutions of nitrate of lead, several precautions must be observed to insure success. The bath which yielded the best results was a rather weak solution of the nitrate, and the current employed was obtained from three small Daniells in series. As it was found that the crystalline deposits obtained with this salt had a constant tendency to grow upward, instead of lying flat on the Fig. 146. as is more generally the case with the acetate solution, an attempt was made to deposit the crystals between two plates of glass, for which purpose the electrodes were laid flat on the receiving plate, and a second glass then laid over all ; but though a slight crystalline deposit occurred at the extreme edge of the cathode, the crystals posi- tively refused to continue their growth beyond that point, from which it became evident that the thin stratum of liquid between the two ELECTRO-DEPOSITION OF IRON. 1^3 1 glasses offered great resistance to the passage of the current. This method was therefore abandoned, and in order to render the printing of crystals obtained from the nitrate of lead solution practicable, it was found necessary, after the crystals had been varnished, to gently bend the more upright crystals downward, by pressing them with the flat end of a lead pencil, by which means the group shown in Fig. 146 was placed fairly under control. Electro-deposition of Iron. Since the publication of the former e litions of this work the author made a great number of experiments in the electrolysis of iron salts, the results of which were recorded in Fig. 148. the Electrician* The object of these experiments was to ascertain the behaviour of solutions of the various iron salts under electrolytic action, with a view to assist those who are engaged in depositing iron for practical purposes, and at the same time to furnish the student with information which might prove useful to him when studying this branch of electro -deposition. After having tried a considerable number of baths prepared from various salts of iron, and worked at different degrees of strength, it was found that weaker solutions almost in- variably yielded more uniform results than stronger ones, and it also * Electrician, Nov. nth and 25th, Dec. i6th and 3oth, 1887, and Jan. i3th, 1888. 532 APPENDIX. appeared that when the iron baths were so adjusted as to the propor- tion of metal per gallon of solution that the anode and cathode sur- faces required to be about equal, that under such conditions the most favourable results were obtained. Of the many solutions tried, those given below were found to yield the most uniform and satisfactory results. Protosulphate of Iron Bath. The solution was prepared from re- crystallised sulphate of iron, in the proportion of 4 ounces of the salt per gallon of water. The bath was first tried in its neutral condition, with electrodes of about equal surface, and the current from a single small Daniell cell, but as the deposit upon the copper receiving plate was of a rather dark colour, a few drops of sulphuric acid were added, and an extra cell connected, when the character of the deposit was greatly improved. A third cell was now added the whole being connected in series when the subsequent deposit became exceedingly white and bright, which character was maintained. At the end of about a couple of hours the copper plate was withdrawn from the bath, when its brilliant appearance resembled that of copper which had been dipped into mercury. The iron anode, which had been freely dissolved, presented a perfectly clean surface. Ammonio- Sulphate of Iron. For an iron-plating bath, the follow- ing proportions were found to give favourable results : ammoiiio- sulphate of iron, 10 ounces ; water, i gallon. To this solution was gradually added a small quantity of acetic acid, which greatly improved the character of the deposit. It was found that with the current from 2 small Daniell cells in series a solution prepared as above gave very uniform deposits of good white colour, though not quite so bright as those obtained from the simple protosalt. Citrate of Iron. A solution of this salt was prepared by digesting recently precipitated carbonate of iron in a moderately strong and hot solution of citric acid, the carbonate being added a little at a time when the neutral point was nearly reached, which became known by the liquid remaining turbid after the last addition of the carbonate had been given. A moderate excess of citric acid solution was then added, when the liquid at once became clear. The solution was then set aside to cool. With the current from 3 small Daniells in series, a very white and perfectly bright film was instantly obtained upon a copper plate, the deposit retaining this character during a prolonged immer- sion. The anode was found to have been freely and uniformly dissolved. The iron deposited from this bath was exceedingly white and brilliant. Double Sulphate of Iron and Potassa. A bath was prepared from a mixed solution of the respective salts, the iron salt being somewhat in excess, say about 4 ounces of sulphate of iron and 3 ounces of sul- ELECTRO-DEPOSITION OF IRON. 533 phate of potash to the gallon of water. With the current from 3 Daniells, a fine white and very bright deposit of iron was obtained upon a copper plate immediately after immersion, and the deposition proceeded very uniformly for about half an hour, when the film became somewhat streaky ; this was remedied, however, by adding more sulphate of potash. After this latter addition, deposition took place very freely, and the anode was considerably dissolved in the course of an hour. There is no doubt that this would be a very good working bath for the deposition of iron, and if rendered faintly acid, it appears to be less susceptible of oxidation in the atmosphere than the ammonio- sulphate of iron solution. Per salts of Iron. It had always been held by experimentalists that metallic deposits could not be obtained from solutions of the persalts of iron ; for instance, Gore states on page 245 of his book that " solutions of persalts of iron yield no metallic deposit, but are reduced to protosalts by the passage of an electric current." The incorrectness of this statement the author fully established by a series of experi- ments with the persalts of iron, from each of which he succeeded in obtaining deposits of metallic iron in some cases in a perfectly reguline condition. Thus, from a weak solution of pernitrate of iron, the metal deposited in a highly comminuted condition upon the cathode, being in the form of a black gelatinous mass, which, when washed and rapidly dried, was found to be highly magnetic iron in a state of very fine division in fact. From a solution of peroxalate of iron a reguline deposit of iron of tolerably good colour was obtained. From a weak solution of perchloride of iron (i drachm of concentrated solu- tion of the perchloride to 3 ounces of water) a fairly bright deposit of metallic iron was obtained, upon a copper plate, with the current from 5 small Daniells in series. A solution of persulphate of iron in about the same proportions was next tried, when a bright deposit of iron at once took place at the corners and lower edges of the cathode, which gradually extended upward in the form of a horseshoe, which character it maintained until the plate was withdrawn. Deposits of iron were also obtained from solutions of the following persalts of iron, with and without the addition of other substances : sesquicitrate of iron ; sesquicitrate of iron and acetate of soda ; persulphate of iron and sulphate of potassa ; pertartrate of iron ; persulphate of iron and sulphate of ammonium ; persulphate of iron and sulphate of soda ; perphosphate of iron ; perlactate of iron, &c. All these solutions were used in an extremely dilute state, and it was not until this con- dition of the electrolyte was reached that the metal would deposit in a reguline form if at all. It thus became evident, from the results referred to, that under suitable conditions of the electrolyte persalts of iron will yield up their metal, and that if such results had hitherto 534 APPENDIX. been unattainable, it is clear that such necessary conditions had not been fulfilled by those who had previously experimented with these silts. Electro-deposition of Alloys. In the summer of 1887 the author tried a great number of experiments in the electrolysis of mixed solu- tions of neutral, or faintly acid, salts of various metals, with a view first, to determine whether alloys could be deposited from such solutions at all as a matter of fact ; and second, whether, if alloys could be deposited from such solutions, baths could be prepared from neutral or slightly acid solutions which might be employed, as a substitute for cyanide solutions, for the practical purpose of coating metals with alloys. The results of these experiments were published from time to time in the Ekctrical Review,* and since several of the compound solutions which were tried yielded results of a somewhat promising character, so far as relates to their application for practical purposes, it may be well to direct attention to them in the present work. It was generally under- stood, prior to the publication of the results of the experiments referred to, that the deposition of alloys from acid solutions was not only prac- tically impossible but contrary to the generally accepted theory, which holds that from a solution of mixed metals the least electro -positive metal is deposited first ; that is to say, the simultaneous deposition of electro -negative and electro-positive metals had always, up to the time referred to, been considered theoretically impossible, although in the case of cyanide solutions (as those of brass and German silver) the accepted law of electrolysis, propounded by Berzelius, had in the case of these alkaline solutions been actually upset in practice. When experimenting with mixed solutions of neutral or acid metallic salts, the first aim of the writer was to determine whether a filmi of brass an alloy of zinc and copper could be deposited from a solution of the mixed metals under any, and if so under what, conditions. For this purpose a mixed solution of the acetates of copper and zinc was first prepared, the latter salt being in excess. The bath was tried at various degrees of strength, with the current from five small Daniell cells in series, until the desired object was obtained, the deposit of a film of unmistakable alloy in the form of brass of very good colour. In the course of this first experiment it was found that when the solution was too strong a powdery deposit of copper alone appeared upon the cathode ; the solution was then weakened by gradual additions of water, and it was noticed that a marked improvement in the character and colour of the film occurred after each successive addition of that fluid, until finally the characteristic yellow deposit of brass was obtained * Electrical Review, Aug. 26th, Sept. 2nd and gth, 1887. ELECTRO-DEPOSITION OF ALLOYS. 535 upon a steel surface. It was found necessary, however, in order te obtain a film of brass of good colour with the solution thus prepared to immerse an exceedingly small surface of anode, that is to say, less than one -fourth of an inch of anode surface only was required to secure a coating of the alloy upon a cathode surface (a steel plate) of at least five square inches. Indeed, when the anode was allowed to merely touch the surface of the solution a steel plate of five square inches of surface instantly became coated on both sides with brass of a good yellow colour, except at the extreme end farthest from the anode, which was tipped with zinc only. In order to modify this, and place an anode of small surface opposite the entire length of the steel plate, a piece of thin brass wire was next employed as an anode, and answered the purpose admirably, for a fresh steel plate became uniformly coated with brass of very good colour, on both sides, almost immediately after immersion in the bath. Under these conditions the deposition of a true alloy was far more prompt than with any ordinary cyanide solution. A steel plate in contact with a strip of zinc immediately became coated with brass in this bath on the contact side, but copper alone was deposited on the opposite side. By simple immersion, a clean strip of zinc be- came immediately coated with a film of brass in the same solution. It thus became apparent that when once the proper condition of the electrolyte was reached, the deposition of an alloy from an acid solution was an exceedingly simple operation, and that an electro -negative and an electro-positive metal could be deposited conjointly from an acid bath as a veritable alloy. If the above results had been obtainable only with mixed solutions of zinc and copper salts, while solutions of other mixed metals failed to yield similar results, an inexplicable problem would have presented itself. But that this was not the case was amply established by further experiments, in which, amongst other alloys, the following were depo- sited, in some cases with remarkable facility : copper and tin, copper and lead, copper and antimony, copper and silver, copper and nickel, and even copper and platinum. In preparing a series of solutions for depositing brass, the author tried the following with success amongst others which were less successful : the sulphates of zinc and copper, citrates of zinc and copper, chlorides of zinc and copper, tartrates of zinc and copper, from each of which combinations he obtained satis- factory films of brass of a good yellow colour, but for all practical purposes he would give the preference to a solution composed of the acetates of copper and zinc. An endeavour was also made to produce a working bath from the double acetates of copper and zinc by the battery process, as it is termed, as follows : A mixture of about equal parts of commercial acetic acid and water was first prepared, and in this was immersed a clean plate of good sheet brass, connected 536 APPENDIX. to the positive pole of a 5-cell Daniell battery ; a rod of carbon, con- nected to the negative pole of the battery, was then immersed in the liquid, which soon assumed a greenish tint near the anode,, which elec- trode kept very bright and clean, indicating that it was being freely dissolved into the solution. The liquid was kept frequently stirred while the electrolysis was proceeding, and at the end of about twenty minutes the carbon, which exhibited traces of deposited metal upon its surface, was withdrawn, and a steel plate substituted, which became partially coated with a yellow film of brass in less than half a minute. The steel plate was then withdrawn, and the carbon again immersed, in order to allow the solution to acquire sufficient metal to form a practical working bath. In about three-quarters of an hour from the commencement of the operation the bath was found to have become suffi- ciently charged with the respective metals zinc and copper to yield a ready deposit of brass of very good colour. The plate was allowed to remain in solution for a few minutes, when it was taken out and well scoured with silver sand, moistened with soap and water, which opera- tion it withstood without stripping in the least degree, showing that the deposited alloy was thoroughly adherent. The film was next scoured with sand and water only, with as much force as possible, to test the tenacity of the film in the severest manner, and it was found that even this severe treatment failed to remove the film, except by wearing it away by long- continued friction. The plate was next replaced in the bath and allowed to receive a fairly good coating ; it was then well scoured with sand, soap and water, and after being well rinsed was burnished with a steel burnisher, but without blistering or strip- ping in the least degree. It was noticed, when applying the burnish- ing tool, that the deposited metal felt exceedingly soft under the pressure of the tool ; the deposit was therefore reguline in the highest degree, while its colour was equal to that of the finest quality of brass. Since the foregoing results were published in the Electrical Review the author was shown by a correspondent some specimens of steel coated with brass, in a solution of the acetates of copper and zinc, as recom- mended by him, and these certainly gave promise that, with a little further development, the electro-deposition of brass from acid solutions would eventually become practical, in the hands of skilful manipulators, for the purposes of art. Although the author's present engagements deter him from pursuing the subject of alloy deposition for awhile, he hopes to resume his experiments at an early date, and to make known some further results which may prove interesting, if not indeed prac- tically useful, to the electro -metallurgist. Coloration and Staining of Metals. In the finishing of ornamen- tal brass work, metal buttons, and various kinds of fancy metal goods, it is often necessary to produce certain artificial effects of colour or COLORATION AND STAINING OF METALS. 537 tone, to render the work attractive to the public eye. These effects are produced by several well-known means, but modifications are con- stantly sought for, with a view to giving variety to manufactured articles. From some experiments which the author tried in this direc- tion some time ago he is now enabled to suggest one or two processes which may be found useful to persons engaged in the various branches of trade in which metal-colouring and staining are necessary operations in the workshop. The processes to which attention is now called may be best treated under separate headings, since they are each applicable to different branches of trade. Colouring Nickel-plated Work. The production of prismatic colours, called metallo- chromes, upon steel and platinum surfaces, by depositing films of peroxide of lead thereon, is described at page 358. In the experiments referred to it was the -writer's desire to obtain similar effects upon polished nickel-plated surfaces, believing that the colora- tions would show more effectively upon the. white surface of nickel - plated brass than upon steel, while at the same time the process could be applied to fancy articles which could not be conveniently made from the latter metal. In carrying out the experiments a series of polished brass plates, well nickel-plated, were employed. A nearly saturated solution of. acetate of lead was next made and carefully filtered. Three small Daniell cells, in series, were used for the current, to the positive pole of which one of the nickel plates was attached, and then laid upon the bottom of a flat dish. The filtered acetate solution was next poured into the dish until the plate became immersed to the depth of about half an inch. The end of the negative wire of the battery was now brought as close to the plate as possible without touching, and there held steadily, when in a few seconds the coloration commenced, in form of the familiar ring, and quickly ex- tended in a series of brilliant iridescent circles. Pieces of thin copper wire, formed into various designs, as a cross, an anchor, a star, &c., were subsequently used, by which very varied and pleasing effects were obtained, which looked exceedingly effective in the nickel-plated surface, more especially when a sheet of white paper was reflected upon it. To render metallo -chromy practically applicable to nickel- plated articjes of ornament, there are several points that must be considered : the coating of nickel must be something more than a mere film, otherwise, when placed in the acetate of lead bath voltaic action will set up between the nickel film and the underlying brass surface, and the nickel will peel off ; a fair coating of nickel there- fore is absolutely essential. The process, moreover, is only effectual on plane surfaces. In producing the colorations care must be taken not to suffer the particles of spongy lead, which deposit upon the end of the negative wire, to fall upon the plate, otherwise they will 53 8 APPENDIX. cause a series of white spots, by preventing the formation of peroxide upon the surface beneath them. It is also important to prevent dust or particles of any kind from depositing upon the plate during the operation. After the bath has been worked for some tune it naturally becomes acid, therefore when in this condition the articles should be quickly removed when the desired effect is obtained, and at once plunged into clean water, for if allowed to remain in the acid bath the peroxide film will rapidly dissolve. When the bath has become slightly acid it is better to pour it into a bottle containing a little carbonate or oxide of lead, and shake it frequently, when, after an hour or so, it may be filtered and again used. The end of the nega- tive wire should be dipped into water and the deposit of lead which attaches brushed off, after each design has been produced, by doing which the chances of particles falling upon the plate are greatly diminished. When electrolysing a series of solutions of lead salts recently, the author noticed some very interesting varieties of peroxide of lead, which formed upon the various anodes employed, and which it will not be out of place to mention here. When electrolysing a solution of the basic nitrate of lead with a platinum anode, the current from three small Daniells, in series, being used, a yellow deposit of peroxide of lead was at first formed upon its suf ace, which was quickly followed by a superb iridescent film on each side of the plate. After about a minute, two rainbow bands appeared upon the upper part of the anode, while the remaining immersed surface assumed, first, a deep crimson colour, which gradually changed to purple. The film was found to be very adherent. In a solution of sulphate of lead in caustic pot- ash, platinum and steel anodes received a golden yellow film, which, even after a prolonged immersion, did not undergo any change of colour. In a solution of lactate of lead, a platinum anode at first be- came coated with a golden yellow film, which was succeeded by a steel grey at the lower part of the plate ; in a few seconds a deep orange colour began to appear at the lower corners, followed by the primary colours in succession, which rapidly blended as in a prism, producing a remarkably fine effect, which could be modified at will by increasing or diminishing the cathode surface. In a solution of sulphecyanide of lead a platinum anode received a rich golden yellow film, which was sustained without further modification in colour during a long, immer- sion. In a moderately strong solution of nitrate of lead a very brilliant iridescent film was produced upon a platinum anode instantaneously ; when the same solution was considerably diluted with water, and a small cathode surface only immersed, these effects were still more striking, though developing more gradually. In a solution of pyro- phosphate of lead a golden yellow film only was obtained upon a COLORATION AND STAINING OF METALS. 539 platinum anode. A solution of salicylate of lead yielded a precisely similar result. In a solution of the benzoate of lead a pale yellow colour was first produced upon a platinum plate, but this was soon succeeded by orange, then deep orange, followed by a slight tendency to iridescence. When the plate, while still wet, was rubbed with the finger, the prismatic colours at once appeared. Colouring or Staining of Brass Surfaces. To give a black stain to brass, a solution of chloride of platinum is usually employed, but since the platinum salt is an expensive one, its employment would necessarily be restricted to work of a special character, or to articles of a superior quality. With a view to obtain a black colour, which would be applicable to large pieces of brass work, and at the same time be less costly than the platinum salt, the author made a series of experiments, the results of which may, it is hoped, be found useful in a practical sense. Being aware that brass was far more difficult to stain, as it is termed, than copper, the following method was adopted to give the effect of a black stain upon brass work, as also varying shades of brown, from a warm chocolate colour to a deep sepia tone. Having tried many different substances, and solutions of various degrees of concentration, the process given below was finally hit upon, and the results obtained were exceedingly satisfactory, both from an artistic and economical point of view. Knowing that the black deposit, or stain, as it is improperly termed, which is produced upon brass more especially by optical instrument makers is very easily rubbed off, it was determined, if possible, to obtain a firm adherent film which would resist ordinary rough usage, so that the staining process would be applicable to ornamental brass of all kinds, but specially so for chandelier work. Since these results could not be obtained upon brass direct, it was resolved to first give the brass work operated upon a slight coating of copper, in the sulphate of copper bath, and to take advantage of the ready susceptibility of this metal to become stained by means of solutions of alkaline sulphides. To carry out this plan, the following routine was adopted : The brass article, after being dipped in the ordinary dipping-acid and well rinsed, was immersed in a sulphate of copper bath composed of i pound of sulphate of copper dissolved in I gallon of water, to which was added i pound of sul- phuric acid. In from five to ten minutes, with the current from a Daniell cell, the deposit of copper was sufficiently thick for the purpose intended, when the article was removed from the bath and plunged into boiling water, the object being to allow it to dry spontaneously. A solution of sulphide of barium (5 grains of the sulphide to each ounce of water) was next poured into a deep vessel, and the coppered brass article, being held by its suspending wire, was immersed in the liquor, when it at once assumed a light brown tone, which gradually 54 APPENDIX. deepened, until, after a few moments' immersion, the surface acquired an intense but brilliant black. The article was then withdrawn and plunged into hot water, then into boiling water, and afterwards set aside to dry spontaneously, which occupied but a few moments. The black film thus obtained was firmly adherent,, and when the smooth surfaces were rubbed with a clean chamois leather they soon acquired a brilliant polish. Other articles of various forms were subsequently treated in the same way, and when it was desired to give a chocolate brown tone to the piece of work, it was simply immersed in the sul- phide bath for about half a minute or so, when a very pleasing brown tone was produced, possessing quite a metallic lustre. Solutions of the sulphides of ammonium, potassium, and sodium respectively were also tried, but in some respects the barium sulphide is to be preferred. It was next resolved to treat a specimen of ornamental brasswork in the following way. The bright surfaces, or parts which were to be burnished and remain yellow, were coated with a film of paraffin, to prevent the copper from being deposited upon such parts. The piece of work was then placed in the coppering bath until a sufficient coating of the red metal was obtained ; it was then plunged into hot water as before, being afterwards dipped in boiling water, which effectually removed the paraffin. When the work became sufficiently cool to handle, certain ornamental parts were painted over with a mixture formed by mixing blacklead and oxide of iron into a paste, with a rather strong solution of the sulphide of barium. Soon after the last- coating of the above paste had been applied the piece of work was placed under a tap of running water, and a soft long-haired brush briskly passed over the surface until the whole of the sulphide paste was removed. As it was found that even with such brisk washing the diluted sulphide had slightly discoloured the copper surfaces which had not been treated with the sulphide, a moderately strong solution of cyanide of potassium was quickly brushed over the whole piece, a portion at a time, each part thus treated being at once placed under the tap, which was kept running for the purpose. In this way the bright red of the* copper became speedily restored, while the blackened surfaces were unaffected. The article was next rinsed in hot water, and finally in boiling water, as before. The plain surfaces of the article were next burnished, and a thin, colourless lacquer finally applied, when the operation was complete. It will be readily seen that ornamental brasswork chandeliers, finger-plates and fenders, for example may readily be treated in the manner described, and exceed- ingly beautiful and artistic effects produced, without involving much more cost than that of skilled workmanship. Crystals of Metallic Tin. "While making some experiments upon the electro-deposition of tin from solutions of its various salts, the CRYSTALS OF METALLIC TIN. 541 author determined to ascertain how the tin crystals so readily obtained from a solution of the protochloride by the simple immersion of a piece of metallic zinc (as in the formation of the well-known "tin- tree"), would arrange themselves when allowed to form upon a flat horizontal surface a plate of glass, for instance as adopted in the case of lead salts as explained on page 528. To produce the tin crystals a mode- rately strong solution of the protochloride was first prepared, which was rendered slightly acid by the addition of a few drops of hydro- chloric acid, and the liquid then filtered for use. A plate of glass, about 7 by 5 inches, was then laid in a flat dish, and a tin anode, connected to the positive pole of a small 3 -cell Daniell battery, was allowed to rest on the glass plate. A strip of brass, about half an inch in width and attached to the negative electrode, was then placed on the opposite end of the glass plate, and the protochloride solution afterward carefully poured into the dish until the plate was completely immersed. In less than half a minute crystals of tin formed upon the cathode, which soon radiated right and left, and gradually ex- tended in the direction of the anode, until (in about two hours or so) they nearly reached that electrode, which was then removed. While the crystals were thus forming, it was noticed that as they approached the anode say within one-third of the whole distance from the cathode they formed with increasing rapidity ; so rapidly, indeed, as to render their growth almost visible to the eye. The group of crys- tals, which laid flat upon the glass, presented a remarkably fine appearance, the various ramifications spreading over the plate some- what like seaweed which has been allowed to expand in water upon a flat surface. The cathode was next carefully removed by separating the brass plate from the crystals attached to it with a penknife, and the brass plate bearing the crystals was gently and cautiously re- moved and allowed to drain upon a pad of blotting paper. The tin solution was then poured out of the dish, and the vessel well rinsed, after which the glass plate was again laid in the dish and water very gradually poured in (so as not to disturb the crystals) until the plate was well covered ; the plate was then carefully taken out and allowed to drain for about half a minute and the washing operation then repeated several times, so as to thoroughly wash away all traces of the tin salt. When the last washing had been effected the crystals were allowed to drain thoroughly, and were afterwards dried before the fire. A coating of photographic varnish was then poured over the plate, which was subsequently mounted in a frame without a backboard, so that the crystals might be examined both by reflected and transmitted light. Crystalline deposits of tin may readily be obtained in the way indicated upon suitable surfaces and applied to decorative purposes, while, on the other hand, photographic copies of the crystals may be 542 APPENDIX. readily obtained, as directed at page 529, and such impressions might be available as designs for art decoration in some of its numerous applications. Tfce Giilcher Rheostat. This useful resistance coil, of which an illustration is given in Fig. 149, is manufactured by the Giilcher Electric Light and Power Company, and is constructed to carry any current, from I to J,ooo amperes, and will be found very useful to electro-platers, since it will enable them to vary the E. M. F. or current at will. By simply moving a readily adjustable slide, the Fig. 149. current density can be regulated to suit the dimensions of the articles in the bath, and thus the rate of deposit may be kept well under the control of the operator. Being mounted upon a slab of slate, there is no combustible material to suffer from the heating of the coil, as is the case with resistance coils mounted upon wood. The author, having frequently had occasion to use the Gulcher rheostat, may say that he found it to answer its purpose admirably. Seamless Metal-coated Tubes. Mr. F. Madeley, of Stafford, produces jointless tubes in the following way : a strip of soft steel, of suitable width and thickness, is turned up into a skelp or tube by any known method, care being taken to make the joint as close as possible. The closed jointed tube is then polished by means of emery bobs in the usual way. The polishing being completed and the joint made quite close, the tube is next placed in an alkaline copper bath and allowed to receive a film of copper ; it is afterwards immersed in a cyanide brassing solution until a sufficient coating of brass is depo- sited. When a stouter casing of metal is required, the tube, after having been coated with copper in the alkaline bath, receives a further deposit of copper in a sulphate of copper bath prior to its immersion in the brassing solution. The tube is then finished by polishing and lacquering. By this process is produced what is known in the trade as a " close joint." 543 USEFUL TABLES. TABLE I. ELEMENTS, THEIR SYMBOLS AND ATOMIC WEIGHTS. Name. I Atomic Weight. Name. 3 I Atomic Weight. Aluminium . Antimony . Arsenic Al. SI). As. 27'5 122' 75' Mercury Molybdenum Nickel . Hg. Mo. Ni. 200' 96- 59' Barium Ba. 137* Niobium Nb. 97-5 Bismuth Bi. 2IO' Nitrogen N. 14' Boron . B. 10*9 Osmium Cs. 199- Bromine Br. 80- Oxygen O. 16-* Cadmium Cd. 112- Palladium Pd. 106-5 Caesium Cs. 133- Phosphorus P. Calcium Ca. 40- Platinum Pt. 197- Carbon C. 12' Potassium K. 39' I Cerium Ce. 92. Rhodium Ro. 104-3 Chlorine Cl. 35'5 Rubidium Rb. 85' Chromium Cr. 52'5 Ruthenium Ru. 104-2 Cobalt . Co. 59' Selenium Se. 79' 5 Copper . Cu. 63'5 Silicon . Si. / -s / 28- Didymium D. 96- Silver . Ag. 108- Erbium . E. (?) Sodium. Na. 23' Fluorine F. 19- Strontium Sr.' 87-5 Gallium Sulphur S. 32* Grlucinum G. 9'3 Tantalum Ta. 138- Gold . Au. 196-6 Tellurium Te. 129' Hydrogen H. i" Thallium Tl. 204' Indium In. IJ 3'4 Thorinum Th. 119- Iodine . ... I. 127' Tin Sn. US' Iridium .>* Ir. 197- Titanium Ti. SO' Iron Fe. 56' Tungsten W. 184' Lanthanum La. 92' Uranium U. 120' Lead . Lithium Pb. L. 207' r Vanadium Yttrium V. Y. 1 Magnesium Mg. 24'3 Zinc . Zn. 65' Manganese Mn. 55' Zirconium Zr. 89-5 The combining weight of oxygen ia 8. 544 USEFUL TABLES. TABLE II. RELATIVE CONDUCTIVITY, OF METALS. Bv L. WEILLKR. Names of Metals. Conduc- tivity. Observations. j Silver, pure ..... 100' These experiments have ICO' been conducted with a 3. Copper, pure super refined and series of bars especially crystallised ..... 99'9 prepared for the pur- 4. Silicium bronze (telegraphic) . 98- pose. These said bars have 5. Copper and silver alloy at 50 per cent. 86-65 been molten at a uniform 78- diameter of about 13 mil- 7. Silicic copper (with 4 per cent, of limetres. They have beon silicon) 75* cut so as to show the 8. Silicic copper (with 12 pei cent, of grain of the metal, and silicon) .... * 54'7 the detached portions g. Aluminium, pure .... 54'2 have then been drawn 10. Tin, containing 12 per cent, of into wires. sodium 46-9 It is on the wires so ii. Siliciura bronze (telephonic) . 35- obtained that the said 12. Plombiferous copper, with 10 per experiments have been cent, of lead .... 3 o- carried out, and of which 13. Zinc, pure ..... 29-9 the results are given in 14. Phosphor bronze (telephonic) . 15. Silicious brass, with 25 per cent, of 29- the table. As regards those alloys zinc 26-49 which can neither easi'ly 16. Brass, with 35 per cent, of zinc 21-15 be drawn nor rolled, such 17. Phosphide of tin . 17-7 as certain phosphides or 1 8. Gold and silver alloy, 50 per cent. . l6'I2 silicides, the measure - 19. Swedish iron ..... 1 6- ments have been taken 20. Pure tin of Banca .... I5-45 direct from the bars ac- 21. Antimonous copper .... 12-7 cording to the method of 22. Aluminium bronze, 10 per cent. 12-6 Sir W. Thomson. 23. Siemens' steel 12- The measurements have 24. Platinum, pure io'6 been taken by means of 25. Amalgam of cadmium, with 15 per a Wheatstone bridge with cent, of cadmium I2'2 a sliding index, a diffe- 26. Mercurial bronze, Drosnier 27. Arsenical copper, with 10 per cent, of 10-14 rential galvanometer and a battery of four cells. arsenic . . . . 9' I 28. Lead, pure 8-88 29. Bronze, with 20 per cent, of tin 8-4 30. Nickel, pure 7-89 31. Phosphor bronze, with 10 per cent. 6-c 32. Phosphide of copper, with 9 per cent. w D of phosphorus . . 4-9 33. Antimony 3-88 USEFUL TABLES. 545 TABLE III. SPECIFIC RESISTANCE OF SOLUTIONS OF SULPHATE OF COPPER. By FLEEMTNG JENKIN. Sulphate of copper. Temperature. Fahrenheit. 57 61 6 4 68 3 75 82 86 Water. 8 parts. 100 parts. 457 437 41-9 4O' 2 37' i 34'2 3^9 12 100 36-3 34'9 33'5 32-2 29-9 27-9 27-0 16 100 3i'2 30-0 28-9 27-9 26-1 24 6 24*0 20 100 28-5 27'5 26-5 25-6 24-1 22-7 22'2 24 100 26-9 25'9 24'8 23'9 22'2 20-7 20'O 28 100 247 23'4 22'I 2I'O 18-8 16-9 l6'0 TABLE IV. SPECIFIC RESISTANCE OF SOLUTIONS OF SULPHATE OF COPPER AT 500 FAHB. By EWING and M ACGBEGOB. Density. Specific resistance. Density. Specinc resistance. 1-0216 1-0318 1-0622 1-0858 1-1174 1-644 i '348 9-87 5-90 473 1-1386 1-1432 1-1679 1-1823 1-2051 (satu- rated). 35'0 34' i 317 30'6 29'3 TABLE V. TABLE OF HIGH TEMPERATURES. Degrees. Fahr. Description. Degrees. Fahr. Description. 977 980 1000 1140 I2OO 1310 Incipient red heat. A red heat. A dull red heat visible in daylight. Heat of a common fire. A full red heat. Dull red heat. 1700 1873 1996 3000 3300 An orange red heat. A bright red heat. A dull white heat. A white heat. Heat of a good blast furnace. USEFUL TABLES. TABLE VI. COMPARATIVE FRENCH AND ENGLISH THERMOMETER SCALES. French, or Centigrade. Cent, or C. English, or Fahrenheit. Fahr. or F. Cent. Fahr. Cent. Fahr. Degrees. Degrees. Degrees. Degrees. Degrees. Degrees. o 32 33 91-4 67 152-6 i 33-8 34 93 -2 68 154-4 2 35-6 35 95 69 156-2 3 37'4 36 96-8 70 158 4 39-2 37 98-6 I59-8 5 38 100-4 72 161-6 6 42'8 39 IO2'2 73 163-4 7 44-6 40 104 74 165-2 8 46-4 105-8 75 167 9 48-2 42 107-6 76 1 68' 8 10 ii 50 SI'S 43 44 109-4 HI'2 g 170*6 12 53-6 45 113 79 174-2 13 55'4 46 114-8 80 176 14 57'2 47 116-6 Bi 177-8 15 59 48 118-4 82 179.6 16 60-8 49 I20'2 83 i8i'4 17 62-6 50 122 84 183-2 18 64-4 123-8 85 185 19 66-2 ! 52 125-6 86 i86'8 20 68 53 127-4 87 188-6 21 69-8 54 129-2 88 190-4 22 7 r6 55 131 89 I92'2 23 73'4 56 I32-8 90 194 24 75'2 57 134*6 91 195-8 25 77 58 136-4 92 197-6 26 78-8 59 138-2 93 199-4 27 80-6 60 140 94 2OI'2 28 82-4 61 141-8 95 203 29 84-2 62 143-5 96 204-8 30 86 63 I45'4 97 206-6 31 87-8 64 147-2 98 208-4 32 89-6 65 149 99 210'2 66 150-8 100 212 TABLE VII. BIRMINGHAM WIRE GAUGE FOR SHEET COPPER AND LEAD. Thick- Diameter Weight per Square (I Foot. || Thick- Diameter Weight per Square Foot. B^W^G. frl^ 138 - Sheet Sheet in Inches. Sheet Sheet 1 Copper. Lead. Copper. Lead. No. inch. Ibs. Ibs. No. inch. Ibs. Ibs. 0000 '454 20*566 26*75 19 042 I '93 2*48 ooo 425 19*252 25*06 20 035 r6i 2-04 00 17*214 22*42 21 032 1*47 1-89 '340 J5-6 20'06 22 028 1-29 1*65 I 300 17*72 23 025 1*14 i '47 2 284 13' 16-75 24 022 roi 1-30 3 259 11*9 15*26 25 020 918 ri8 4 2 3 8 ii' 14-02 26 018 826 ro6 5 220 10*1 1-2-98 27 016 735 '945 6 203 9'32 11-98 28 014 642 826 7 180 8*25 10-63 29 013 '597 767 8 165 7'59 973 30 '012 708 9 148 6*8 8-72 31 "OIO 480 600 10 134 6*16 7-90 32 009 420 '532 ii 120 5*51 7-08 33 008 370 472 12 109 5 '02 6-42 34 007 323 413 13 095 4'37 5'6o 35 00 5 262 309 14 083 4-90 36 004 194 236 15 072 3*31 4'25 16 e6 5 3-00 3-83 17 058 2*67 3'42 18 049 2*25 2-90 TABLE VIII. NEW LEGAL STANDARD WIRE GAUGE ISSUED BY THE STANDARDS DEPARTMENT OF THE BOARD OF TRADE. CAME INTO FORCE MARCH IST, 1884. Descriptive No. B. W. G, Equivalents in parts of an inch. Descriptive No B. W. G. Equivalents in parts of an inch. Descriptive No, B, W. G. Equivalents in parts of an inch. 7/o 500 13 092 32 0108 6/0 464 14 080 33 oioo 5/o 432 15 072 34 0092 4/o 400 16 064 35 0084 3/o 372 17 056 36 0076 2/O 348 x8 '048 37 0068 O 324 19 040 38 0060 I 300 20 036 39 "0052 2 276 21 032 40 0048 3 252 22 028 4i 0044 4 232 23 024 42 0040 5 '212 24 'O22 43 0036 6 192 25 020 44 0032 7 I 7 6 26 018 45 0028 8 160 27 "0164 46 '0024 9 144 28 0148 47 'O020 10 128 29 OI 3 6 48 'OOl6 ii 116 30 0124 49 OOI2 12 104 31 0116 50 ooio 548 USEFUL TABLES. TABLE IX. CHEMICAL AND ELECTRO - CHEMICAL EQUIVALENTS. Name of Substance. Symbols. Equivalents. Weights decomposed by one ampere in one hour. Chemical. Electro- Chemical. Hydrogen . . Aluminium . . . H Al i 137 mgr. 0-01036 0-1425 grammes. 0-0375 Antimony Sb 122 1-2688 4'575 Arsenic As 75 0-7800 2-8125 Barium Ba 68*5 0-7124 2-5687 Bismuth , ., Bi 2IO 2-184 7'875 Boron . B II 0-1144 0-4125 Bromine . ' . Br 80 0-832 3 Cadmium . . Cd 56 0-5824 2*095 Calcium . . . Ca 20 0-208 0*75 Carbon . ; . C 6 0*0624 0-2250 Chlorine . . Chromium . Cl Cr 35'5 26-2 0-3692 0-2725 i*33i2 0*9825 Cobalt Co 29*5 0-3068 1*1062 Copper Cu SI'S 0-3367 1*1925 Fluorine . , F 19 0*1976 0*7125 Gold .... Au 98*3 1*0223 3-6862 Iodine . ''. I 127 1-3208 4-7625 Iron . . Fe 28 0-2912 Lead .... Magnesium . Pb Mg 103-5 12*2 1-0764 0-1269 3-8812 0-4575 Manganese v Mn 27-5 0-286 1-0312 Mercury ... Hg 100 1*036 3'75 Nickel Ni 29*5 0-3068 1*1062 Nitrogen N 14 0-1456 0*5250 Oxygen . ^ . Palladium . Pd 8 53'2 0-0832 0-5533 0-3 1-9947 Phosphorus . . P 31 0-3224 1*1625 Platinum . . Pt 98-6 1*0254 3' 6 975 Potassium . . K 39-i 0-4066 1-4637 Selenium . , Se 39-8 0-4I39 Silver .... Ag 108 1-1232 4*05 Silicon . . Si 14 0*1456 0-5242 Sodium . . Na 23 0-2392 0-8625 Strontium . . Sr 43-8 0*4555 1-6425 Sulphur . . S 16 0-1664 0-6 Tin Sn 59 0-6136 2-2125 Zinc . . Zn 32-7 0-3401 1-2243 USEFUL TABLES. 549 TABLE X. CHEMICAL AND ELECTRO-CHEMICAL EQUIVALENTS OF SOME COMPOUND SUBSTANCES. Name of Substance. Symbols. Equivalents. Weights decomposed by one ampere in one hour. Chemical. Electro- Chemical. mgr. grammes. Acetic acid C 4 H 4 4 60 0-6240 2-25 Hydrochloric acid (gas) Nitric acid (monohydrated) . HC1 NO 6 H 36-5 63 0-3796 0-6552 1-3687 2-3625 Oxalic acid . C 4 H 2 8 90 0-936 3*375 Phosphoric acid (hydrated) . P0 53 HO 98 1-0192 3-675 Sulphuric acid (monohy- drated) Tartaric acid S0 4 H C 8 H 6 12 49 150 0-5096 1-56 1-8375 5-625 Iron sulphate FeSO 4 yHO 139 i '4456 5'2i25 Nickel NiSO 4 7HO 1 40' 5 1*4612 5-2687 Potassium ,, KS0 4 87-1 0-958 3-2662 Sodium ,, NaSO 4 7 1 0-7384 2-6625 Zinc ,, ZnSO 4 80-7 0-8393 3*0262 Ammonia Ammonium chloride NH 4 O,,HO NH 4 C1 35 53'5 0-3640 0-5564 1-3125 2-0062 cyanide C 2 N 2 H 4 44 0*4576 1-65 sulphate N 2 H 8 S0 4 84 0-8736 3-15 Nickel chloride NiCl 65 0-676 2'4375 Gold perchloride Silver cyanide Au 2 Cl 3 AgC 2 N SOS'S 134 3-1564 I-3936 11-3812 5*025 Potassium cyanide KC 2 N 65-1 0-667 2-4412 Copper sulphate (anhydrous) (crystallised) CuSO 4 CuS04 5 HO 79'7 1247 0*8289 1*2969 2-9887 4-6762 550 USEFUL TABLES. XI. TABLES OF WEIGHTS AND MEASURES. I pound i ounce i drachm i scruple i pound I ounce I pennyweight i gallon i pint i ounce i drachm APOTHECARIES' WEIGHT. equals TROY WEIGHT. 1 6 ounces. 8 drs. (480 grains).* 3 scruples. 2 grains. 12 ounces. 20 pennyweights (dwts . ) or 480 grains.* 24 grains. IMPERIAL MEASURE. equals . . . 8 pints. ,, . . 20 ounces. ,, . . . 8 drachms. 60 minims. FRENCH OR METRICAL SYSTEM. French Weight. Kilogramme, i ,000 grammes . equals Gramme (the unit) . . ,, 2 Ibs. 3f ozs. nearly. 15-432 grains. French Measure of Volume. i litre (the unit) . " . . equals . 34 fluid ounces nearly. Long Measure. Metre (the unit) . . . equals . 39-371 inches. Decimetre (loth of a metre) . ,, . 3'937i ,, Centimetre ( i ooth of a metre) . ,, . 0-3937 ,, Millimetre (loooth of a metre) . ,, . 0-0393 ,, * An ounce Avoirdupois is only 437-5 grains. WORKS RELATING TO ELECTRO -DEPOSITION. GALVANOPLASTIC AET. M. H. Jacobi. Translated by W. Stur- geon. 1841. ELECTEOTYPING, MEMOIE ON. F. Zantedeschi. Venice. 1841. ELECTEO-PLATING OF GOLD AND SILVER APPLIED TO HOEOLOGY. A. O. Mathey. Paris. 1855. AET OF ELECTEO-PLATING. C. H. Schmidt. 2nd Edition. "Weimar. ELECTED - CHEMICAL PEOCESSES FOE GOLD, ETC., PLATING. Perrot. Paris. 1845. ELEMENTS OF ELECTEO-METALLUEGY. Alfred Smee. 3rd Edition. 1851. ELECTEO- GILDING AND SILVEEING. W. Sturgeon. 2nd Edition. 1843. MANUAL OF ELECTBO-METALLUEGY. George Shaw. 2nd Edition. 1844. CONTEIBUTIONS TOWAEDS THE HlSTOEY OF ELECTEO-METALLUEGY. H. Dircks. 1844. ELECTEOTYPE MANIPULATION. C. Vincent Walker. Part I., 2Qth Edi- tion. 1859. Part II., 1 6th Edition. GALVANOPLASTLE. ENCYCLOPEDIE-ROEET. 2 vols. Paris. 1854. GILDING AND SILVEEING BY ELECTEO - DEPOSITION. F. Selmi and others. 1856. ELECTEOTYPING AND ELECTEO-PLATING. A. G. Martin. Vienna. 1856. THEOEY AND PEACTICE OF ELECTEO-DEPOSITION. G. Gore. 1856. REPEETOEIUM DEE GALVANOPLASTIK UND GALVANOSTEGIE. A. Martin. 2 vols. Vienna. 1856. HISTOEY OF ELECTEO-METALLUEGY. Henry Dircks. 1863. ELEMENTS D'ELECTEO-CHEMIE. M. Becquerel. Paris. 1864. KATECHISMUS DEE GALVANOPLASTIK. F. Martius MatzdorfL Leipzig. 1868. ELECTEO-DEPOSITION OF COPPEE AND BEASS. W. H. Walenn. 1870. ELECTEO-CHEMICAL RESEAECHES. E. Fremy and A. E. Becquerel. Paris. 1852. SCIENTIFIC RESEAECHES IN ELECTEO-CHEMISTEY. W. Sturgeon. 1850. ELECTEO -CHEMISTEY WITH POSITIVE RESULTS. C. Chalmers. 1858. HANDBUCH DEE GALVANOPLASTIK. Dr. F. Binder. Weimar. 1884. GALVANOPLASTIC MANIPULATIONS. A. Roseleur. Philadelphia. 1872. MANUAL OF ELECTEO-METALLUEGY. J. Napier. 5th Edition. 1876. AET OF ELECTEO-METALLUEGY. George Gore, LL.D. 2nd Edition. 1884. 552 WORKS RELATING TO ELECTRO-DEPOSITION. ELECTRO-PLATING. J. W. Urquhart. 1880. ELECTROTYPING. J. W. Urquhart. 1881. ELECTRO-METALLURGY PRACTICALLY TREATED. Alexander Watt. 8th Edition. 1882. ELECTROLYSE, GALVANOPLASTIK UND REINMETALLGEWINNUNG. E. Japing. Leipzig. 1883. GALVANOPLASTIC MANIPULATIONS. H. Wahl. Philadelphia. 1884. ELECTROLYSE, RENSEIGNEMENTS PRATIQUES SUR LE NICKELAGE, &o. H. Fontaine. Paris. 1885. Besides the above works, there are articles respecting electrolytic operations in the following books and periodicals to which reference may be made : Tomlinson's Cyclopaedia ; Ure's Dictionary of Arts, &c., Supplement; Watts' Chemical Dictionary; Chemistry Applied to the Arts ; Spon's Encyclopaedia ; Wagner's Technology ; Gmelin's Handbook of Chemistry, Vol. I. : Sprague's Electricity ; Modern Applications of Electricity. Hospitaller ; The Chemist, 1840 to 1858 ; Chemical News; Timmins' Midland Hardware District, 1866 ; Sevan's "British Manufacturing Industries," 1876; Encyclopaedia Britan- nica, vol. viii., 1878 ; Electrical Review, 1887-8 ; Electrician, 1887-8 ; Engineering and Mining Journal, New York ; Dingier 1 8 Polytechnic Journal ; Elektrotechnische Zeitschrift. Berlin. INDEX. A CCOUTREMENT, army, gilding, A 185 Accumulation of lumps on pulleys, 488 Accumulators, 16 Acetate of calcium, 297 copper, 372, 475 lead, 357, 475 lime, 296 nickel, 296 silver, 195 zinc, 346, 372 Acetic acid, 198, 297, 476 Acid, arsenious, 374 benzoic, 296 , boric, 295, 296 citric, 296 dip, nitric, 236 dipping, 289, 481 fumes, 493 poisoning by, 512 hydrochloric, 187, 220, 481 hydrocyanic, 160, 271, 481 >, poisoning by, 5 10 hydrofluoric, 120 muriatic, 236 pickle, 200 nitrate of bismuth, 355 nitric, fuming, 236, 481 nitro-hydrochloric, 476 -sulphuric, 180 nitrous, 236 prussic, 227, 481 pyroligneous, 476 stripping, for nickel-plated ar- ticles, 470 Acid, sulphuric, 234, 242, 486 pickle, 193 sulphurous, gas, 397 tartaric, 334 Acids, corrosive, poisoning by, 511 Acierage, 340 Action of the electric current upon compound substances, 74 Adamantoid boron, 449 Adams' process for metallising moulds, 131 Mr. I., process for nickel- plating, 292 Advantages of gas engines in driv- ing dynamos, 491 Air-bubbles, to prevent the forma tion of, 93 Albata, 502 Albert chains, gilding, 177, 179 Alkalies, poisoning by, 511 Alkaline coppering solutions, 147 Alum, 199 ammonia, 331, 332 potash and soda, 332 rock, 362 and tin, solution of, 332 Alumina, 292, 332 sulphate of, 332, 362 Aluminium, 444, 513, 514 alloys, 444 Burghardt and Twin- ing's process, 513 bronze, 448, 514 deposition of, 360, 513 deposition of, Goze's process, 363 554 INDEX. Aluminium, deposition of, Jeancon's process, 363 deposition of, Thomas and Tilley's process, 362 hydrated oxide of, 444 and potassium, double salt of, 363 pyro-plating with, 266 silver, 448 and sodium, double chloride of, 361 solutions, 362 Aluminous minerals, 449 Alloy, Hercules, 448 of platinum and silver, 391 Alloys, 500 aluminium, 444 copper and bismuth, 501 palladium, 501 tin, 501 zinc, 501 density of, 501 electro-deposition of, 366, 379, 534 gold and antimony, 501 bismuth, 501 cobalt, 501 copper, 501 iridium, 501 iron, 501 lead, 501 nickel, 501 silver, 501 silver, deposition of, 390 tin, 501 zinc, 501 tin and antimony, 501 lead, 501 palladium, 501 zinc and antimony, 501 Amalgam of cadmium, 514 gilding, 202 gold, 203 Amalgamating zinc, 4, 92 Amalgams, 502 American cheap goods, re-nickeling, 3i9 American formulae for brassing solu- tions, 377 potash, 235, 286, 476 Amianthus, 76 Ampere, or unit of quantity, 84, 87 Ammonia alum, 331, 332 aurate of, 172, 186 bicarbonate of, 226 bichromate of, 390 carbonate of, 225, 296 liquid, 296, 481 oxalate of, 292 sulphate of, 295, 332 Ammonio-chloride of palladium so- lution, 354 -nitrate of copper solution, 479 -sulphate of cadmium so^ lution, 363 -sulphate of copper, solu- tion of, 479 -sulphate of iron solution, 344 -sulphate of magnesia,39O Ammonium, chloride of, 294, 299, 344 sulphide of, oxidising with, 271 Ammoniuret of gold, 172 Anelectrode, 71 Animal substances, copying, 116 Anions, 71 Annatto, 207 Annealing copper wire, 145 Anode, 71 brass, 378 carriers, 434 charcoal, 362 and iron, 342 of coke and zinc, 441 copper, gilding with, 213 galena, 442 German silver, 389 gold, 171, 183 lead, 358 INDEX. 555 Anode, palladium, 354 platinum, 187, 349 platinum and silver, 391 wire, 178 rods, 308 silver, 221 steel, 341 tin, 390 zinc, 345, 346 Anodes, brass, cleaning, 392 bullion, 428 carbon, 438 cast cobalt, 352 nickel, 329, 482 of chromium alloj'S, 390 cobalt, 351 copper, 144 dirty, 278 gas carbon, 343 gold, worn, 211 iron, 341, 397 n wire, 343 nickel, 282, 284, 482 pure copper, 399 rolled cobalt, 352 nickel, 329, 482 silver, 274 tin > 335 worn, 274 Antidotes and remedies in case of poisoning, 509 Antimoniate of soda, 430 Antimonious copper, 514 Antimony, 39, 97, 501, 513 butter of, 355 chloride of, 355 deposition of, 355 deposition of, by simple immersion, 356 oxychloride of, 356 potassic tartrate of, 356 solutions of, 355, 356 sulphuret of, 355 terchloride of, 355 teroxide of, 356, 430 tersulphuret of, 356 Antique, or green bronze, 386, Antique silver, imitation, 269 Application of nickel-plating, 280 of Ohm's law to com- pound voltaic circles, 86 Applying the amalgam, 203 stopping-off varnishes, 47 1 Aqua fortis, 236, 357, 476 regia, 195, 476 Argentiferous copper pyrites, 436 galena, 435 Argol, 238 Argyrometric scale, Roseleur's, 262 Armature, 22 intensity, 25 quantity, 25 Army accoutrement work, gilding, 185 Arrangement of baths for electro- lytic refining, 427 of battery, 1 10 for depositing tin, 335 of electrolytic refining plant, 399 of nickeling plant, 306 of silver-plating bath, 241 Arsenic, 374, 501, 513 Arsenical copper, 514 Arsenious acid, 374 Arsenite of soda, 430 Articles falling into bath, 276 Artificial magnet, 21 Asbestos, 76, 439 Asphalte, 119 Augmentation of the conductivity of nickel baths, 326 Aurate of ammonia, 172, 186 Auriferous pyrites, 439 Autogenous process, 281 TjABBINGTON'S battery, 7 -^ Bacco's brassing solution, 376 Backing pan, 133 -up metal, 133 Balance, plating, 261 556 INDEX. Bar-fittings, &c., nickeling, 311 Barium, 513 sulphide of, 500 Barometer, &c., scales, silvering, 231, 232 Bath, arrangement for electrolytic refining, 427 ,, articles falling into the, 276 brick, 181 cold, for all metals, 37^7 cold gilding, observations on, 174 dust on the surface of, 278 electrotyping, 132 for gilding steel, 186 177 Record's, 176 gold, management of, 2ii iron, 343 keeping up strength of, 393 metal, 502 motion of articles in the, 243 nickel, augmentation of con- ductivity of, 326 nickel, for facing electrotypes, 320 pickling, for cast iron, 290 plating, arrangement of, 241 ,, preparation of new work for, 233 potash, 179, 235 for nickel-plating, 286 precautions to be observed when filling the, 274 pyrophosphate of tin, 334 recovery of dropped articles from, 328 stripping for gold, 469 nickel, 319 silver, 252, 467 sulphate of copper, Gramme's for tinning zinc, 332 experiments with, 41 1 Battery, arrangement of, 1 10 Babbington's, 7 bichromate, 15 Battery, brass solution prepared by, 378 Bunsen's, n Callan's iron, 1 1 compound Grove, n connections, 274, 279 constant, 8, 51 Cruickshank's trough, 6 deposition of platinum by, 350 C. Watt's thermo-electric, 42 Daniell's, 8 Gassiot and Crosse's water, 15 Grove's, 10 Leclanche's, 15 Marie-Davy, 16 Maynooth, n nickel-plating by, 284 nitric acid, 10 Noe's thermo-electric, 49 Planters secondary, 17 plating, 242 separate, electrotyping by, no Smee's, 9, 181 stripping silver by, 468 twin-carbon, 284 Walker's graphite, 13 water, 15 Wollaston's, 8, 181, 242 Batteries, arrangement of, 1 10 constant, 51 constancy of, 494 electrotyping, 132 electromotive force of, 88 management of, 494 relative intensity of, 495 power of, 494 secondary, 16 separate, electrotyping by, no thermo-electric, 42 Beardslee's cobalt solution, 353 Becquerel's cobalt solution, 353 gold solution, 168 INDEX. 557 Becquerel's process for treating gold, &c., ores, 434 solution for metallo- chromes, 359 ., thermo-pile, 45 Beer, scratch-brushing with, 179 Beeswax, 95, 386, 471 Bell-metal, 503 Belt, fixing the, 488 leather, 458 Belts, coming off pulleys, 488 driving, 487 jointing, 488 main driving, 487 and pulleys, accumulation of lumps on, 488 slipping off, 493 Benzine, 125, 342 Benzoic acid, 296 Benzol, 120 Bessemer bronze, 386 bronzes, 121 Bessemer's, Sir Henry, early experi- ments in depositing copper, 60 Bibulous paper, 172 Bicarbonate of ammonia, 226 Bichromate of ammonia, 390 battery, 15 of potash, 15 Bicycles, nickeling, 313 second - hand, nickeling, 3i4 spokes, nickeling, 313 Binding screws, 498 wire, 117 Binoxide of mercury, 231 nitrate of, 189 Bird's, Dr. Golding, experiments, 62 Birmingham ware, 251 Bismuth, 39, 501, 513 acid nitrate of, 355 and ammonium, double chloride of, 355 cyanide solution of, 355 deposition of, 355 nitrate, solution of, 355 Bismuth, subnitrate of, 355 Bisulphide of carbon, 119, 228, 342, 476 of mercury, 16 Bisulphite of soda, 194, 231, 374 sodium, 231, 296 Bitartrate of potassa, 189, 230 Bits, spurs, &c., nickeling, 308, 316 Black bronze, 384 enamel, 273 lead, 385, 484 metal, 404 Bleaching powder, 274, 392 Blende, zinc, 439, 443 Blister copper, 401 Blood-stone burnishers, 458 tools, buff for polishing, 459 Blue metal, 404 Bluestone, 91, 485 Bob, lime, 455 Bobs, polishing, 452 Boettger's cobalt solution, 354 ferrocyanide solution of iron, 344 solution for depositing platinum, 351 Book clasps, &c., nickeling, 322 work mounting, 135 Borax, 199, 267 Boric acid, 295, 296 , oxide, 449 Boron, 447, 513 adamantoid, 449 bronze, 449 Boxwood sawdust, 187, 267 Brackets, insulating, 306 Brass, 503 anode, 378 anodes, cleaning, 392 articles, small, nickeling, 306 button, 504 for castings, 503 clock-dials, &c., whitening, 232 concentrated solution of, 393 553 INDEX. Brass and copper articles, solution for stripping nickel from, 470 and copper, solution for gild- ing, 159 and copper work, nickeling, 302 deposits, thick, 378 electro-deposition of, 366 &c., electro-plating, 250 finishing, 454 malleable, 503 pins, electro-tinning, 331 polishing, 451 red, 503 rods, 242 sheet, cathodes, 433 silicious, 514 solder, 504 solution prepared by battery, 378 solution for rough cast iron, 377 taps, nickeling, 305 for turning, 503 for wire, 504 work, cast, nickeling, 330 Brassed, electro, work, dipping, 387 electro, work, lacquering, 387 Brassing different metals, 393 -' electro, cast-iron work, 379 lead, pewter, and tin work, 381 ,, notes on, 392 observations on, 382 wrought-iron work, 380 zinc work, 380 in hot solutions, 394 Newton's processes, 371 Person and Sire's process, 378 Wood's process, 372 solution for cast-iron work, 393 , Dr. Heeren's, 373 Morris and John- son's, 372 Brassing solution, Russell and Wool- rich's, 372 Wood's, 372 solutions, 367, 368 American formu- lae for, 377 Brunei and Co.'s, 369 De Salzede's, 371 Newton's, 371 Roseleur's, 373 ^ Walenn's, 374 Bright and dead gilding in parts, 205 dead lustre, 188 lustre, dip for, 236 plating, 22,8, 277 solution for, 228 Brightening s.olution, 229, 276 Britannia metal, 258 &c., electro-plating 250 gilding, 167 lead, &c., gilding, 216 tin, &c., nickeling, solution for, 298 Brooches, gilding, 177, 179 Bromine, 513 Bromide of cadmium, 364 Bronze, aluminium, 448, 514 Bessemer, 121, 386 black, 384 boron, 449 cobalt, 391 colour, green, 392 electro-deposition of, 366, 388 green, 385 magnesium, 391 mercurial, 514 phosphor, 514 powder, tin, 131 powders, 386 metaUic, 484 silico-aluminium, 449 silicon, 444 INDEX. 559 Bronze, silicious, 514 solution, for gilding, 160 steel, 386 Bronzes, colour of, 392 electro, 192 gilding, with amalgam, 206 silicon, 449 Bronzing ceramic ware, 387 chocolate tone, 385 electro-brassed work, 384 electro-brassed zinc work, French method, 386 the electrotype, 101 fenders, 384, 387 gun barrels, 357 paste, 385 salt, 357 solution, 388 solutions, 371 stove fronts, 384 umbrella stands, 387 Brushes, 245 bristle, 455 camel-hair, 269 circular, 456 cow-hair, 455 hog-hair, 303 scouring, 245 scratch, 179, 248 Brushing, scratch, 247 Bubbles, gas, removing, 322 Buff, 258 for polishing bloodstone tools, 459 sticks, 258 Buffing old work after stripping, 253 Buffs, 455 for polishing burnishers, 459 Building, 128 iron, 128 Bullion anodes, 428 plates, 428 Bull-neck leather, 452, 456 Bunsen cell, 178 Bunsen's battery, 1 1 Burning the work, 281, 304 Burnishers, 458 Burnishers, buffs for polishing, 459 steel, 458 Burnishing/ 458 \electro-gilt work, 460 preparing the tools for, 458 preparation of work for, 459 silver and plated work, 459 Butter of antimony, 355 Button brass, 504 Buttons, hooks and eyes, &c., whiten- ing, 230 Busts, plaster, copying, 112 CADMIUM, 97, 503, 513 amalgam of, 514 ,, ammonio - sulphate solu- tion of, 363 bromide of, 364 ^ deposition of, 363 deposition of, Russell and Woolrich's process, 363 sulphate of, 364 Caesium, 513 Calamine, 439 Calcium, 447, 513 acetate of, 297 carbonate of, 297 chloride of, 362 sulphide of, 292 Callan's iron battery, n Candlesticks, old plated, 256 Carbon, 329, 513 anodes, 438 bisulphide of, 228, 342, 476 electrode, 171 gas, anodes of, 343 granulated, 445 twin, battery, 284 Carbonate of ammonia, 225, 296 of calcium, 297 of lime, 454? 485 of magnesia, 343 ores of copper, 396 of potash, 101, 221, 476 560 INDEX. Carbonate of copper, 146 ,, of silver, 224 of zinc, 439 Carmine, lac, 385 Carriers, anode, 434 Case-filling and steam-heating tables, 126 CassePs process, electro-chlorination of gold ores, 438 Cast-brass work, nickeling, 330 ,, cobalt anodes, 352 Cast-iron, coppering, 144 dogs, bronzing, 387 pickling bath for, 290 rollers, coppering, 144 rough, brass solution, for, 377 work, brassing solution, for, 393 work, cleaning for nickel- plating, 287 work, electro - brassing, 379 work, nickeling, 317 work, preparing of, for zincing, 346 work, scouring, 380 Cast nickel, 284 anodes, 329, 482 Castings, brass for, 503 Cathelectrode, 71 Cathode, 71 Cations, 71 Causes which affect the colour of the deposit, 181 Caustic alkali, 235 ley, 390 lime, 231 potash, 287, 476 soda, 332 Cell, porous, n, 63 origin of the, 63 single, process, 91 single, process, deposition of copper by, 91, 92, 106 single, process, deposition of tin by, 334 Cementation copper, 396 Cerium, 513 Ceylon graphite, 128 Chain work, nickeling, 318 Chains, gilding, 208 metal, gilding, 180 Chalices, gilding, 187 Chalk, prepared, 231 Chamois leather, 184, 271 Chandeliers, oxidising, 271 Characteristics of cobalt, 352 electro-plate, 259 metals : 498 Charcoal, 272 anode, 362 furnace, 163 granular, 447 iron anode, 342 Cheap fancy work, nickeling, 306 goods, American, re-nickeling, 3i9 goods, French, re-nickeling, 3i9 goods, German, re-nickeling, 3i9 jewellery, French gilding for, 160 jewellery, gilding, 212 Chemical action, 4 electricity, 2 powers of the voltaic pile, 70 Chili saltpetre, 467 Chloride of aluminium, 360 aluminium and ammo- nium, 363 ammonium, 15, 299, 344, 484 antimony, 355 bismuth, 355 calcium, 362 cobalt, 352, 519 copper, 274 gold, 187, 477 gold, preparation of, 157 gold, solution of, gilding by immersion in, 159 INDEX. Chloride of lead and sodium solu- tion, 357 lime, 392 magnesium., 365 mercury, 362 palladium and ammoni- um, solution of, 354 platinum, 270, 477 platinum, preparation of, 349 platinum, solution of, 384 silver, 220, 463 paste, 231 sodium, 189, 292, 326 tin, 331, 332 zinc, 443, 477, 5<>7 Chlorination of gold ores, 438 silver ores, 435 Chlorine, 392, 513 nascent, 437 Chloroform, 229 Chromate of lead, 385 Chromium, 513 alloys, anodes of, 390 solution of, 390 deposition of, 364, 390 protoxide of, 365 sesquioxide of, 365 Chrome yellow, 385, 471 Chutter's dynamo-electric machine, 488 Circl% simple Voltaic, 4 Circular brushes, 456 Citrate of nickel, 296 Citric acid, 296 Clamond's thermo-electric pile, 45 thermo-pile, section of, 47 Classification of elements, electro- lytic, 89 Cleaning cast-iron work for nickel- plating, 287 conducting rods, 242 suspending rods, 276 Cleanliness, 493 Clearing the mould, 105 Clock cases, gilding, 195 9 Clock dials, brass, &c., whitening, 231, 232 faces, silvering, 231, 232 Clocks, gilding, 163 Cloth, coppering, 121 Coating non-conducting substances, 156 copper plates with iron, solution for, 508 Cobalt, 351, 501, 513 and ammonium, double sul- phate of, 352 anodes, 351 bronze, 391 characteristics of, 353 chloride of, 352, 519 electro-deposition of, 351, 517 ore, 352 salts, 351 solution, Beardslee's, 353 Becquerel's, 353 Boettger's, 354 Prof. Thompson's, 520 ,, solutions, 353, 518 sulphate, 518 Cobalus, 352 Coffee-pots, electro-plating, 246, 254 Coffin nails, &c., whitening, 230 Coil, resistance, 275, 308, 496 Coils, resistance, 284 Coke and zinc anode, 441 Colossal statues in electrolytic cop- per, 140 Colour of bronzes, 392 of deposit, causes which affect the, 181 of electro-deposited gold, 196 ,, warm bronze, 385 Coloured gold, 183 jewellery, 199 Colouring, dry, 199 gilt work, 162 ,, or hand-finishing, 457 mercury gilding, 204 mixture, ormolu, 206 nickel-plated work, 537 INDEX. Colouring, processes, 198, 539 salts, 162, 183 ,, wet, 199 Cold bath for all metals, 377 baths, gilding in, observations on, 174 eflfectro-gilding solution, 172 gilding, 195 stripping solution, 253 for silver, 468 Commercial crocus, 264 cyanide, to determine the strength of, 479 cyanide of potassium, observations on, 221 Common pewter, 503 salt, 291 salt in nickel solutions, 325 Commutators, 28 Comparative French and English thermometer scales, 516 Compo, crocus, 455 rouge, 455, 457 Composition of baths for electro-etch- ing, 152 of bath for gilding steel, 1 86 crocus, for dollying, 327 etchings-ground, 151 moulding, 125 nielling, 273 for stopping off, 471 Compound Grove battery, n magnet, 24 substances, action of elec- tric current upon, 74 wire, 146 Concentrated platinising solution, 349 solution of brass, 393 of tin, 336 Conducting rods, 242, 282, 308 wires, 306 Conductivity of metals, 87 M of nickel baths, aug- mentation of the, 326 Conductivity, relative, of metals, 514 superior, of hot gilding solutions, 1 66 Conductors and insulators, 80 Connecting the mould to the wire, 109 Connection gripper, Hoe's electric, 130 Connections, battery, 274, 279 ,, cleaning, 279 Constancy of batteries, 494 Constant battery, 8, 51 Contact, electrical, 5 Continental method of gilding watch movements, 188 Continental method of gilding zinc articles, 193 Copal varnish, 471 Copper, 404, 502, 513 acetate of, 475 ., ammonio-nitrate of, 479 sulphate of, 479 anode, gilding with, 213 anodes, pure, 399 . antimonious, 514 -antimony couple, 42 arsenical, 514 baths, composition of, 152 blister, 401 and brass articles, small, nickeling, 306 and brass articles, solution for stripping nickel from, 470 and brass work, nickeling, 302 carbonate of, ores, 396 cementation, 396 chloride of, 27 (. coating non-conducting sub- stances with, 156 colossal statues in, 140 cyanide of, 372, 463 depositing bath for electro- typing, 132 depositing baths, alkaline, 147 depositing, on glass, porce- lain, &c., 120 Copper deposition of, by dynamo- electricity, 139 deposition of, by separate battery, no deposition of, by single cell process, 91 deposition of, on iron, 141 deposition of, by Oudry's process, 144 electro-metallurgy of, Dr. C. W. Siemens on, 401 electro-soldering, Eisner's ex- periments in, 472 electrolytic, advantages of, 426 electrolytic, its high conduc- tivity, 429 electrolytic refining of, by dynamo-electricity, 403 electrolytic refining of, by magneto-electricity, 399, 401 electrolytic refining of, by separate current, 397 electrolytic treatment of, 399 electrolytic treatment of, in Genoa, 421 Elkington's process of refin- ing, by electrolysis, 400 Klein's process of depositing iron upon, 341 moulds, making, by electro- lysis, 153 from ores, Marchese's process for electrolytic extraction of, 437 oxide of, 267, 396 phosphide of, 514 pimple, 401 plates, electro-etching, 151 plates, engraved, facing with iron, 340 plates, solution for coating, with iron, 508 plates, steel facing, 508 INDEX. no- ate Copper, cell on, " y's C. * 5X- of, uc- n by by 99, " by . of, in fin- i ing tro- ;ess 1 ion I rith ng, , plombiferous, 514 precipitation of, 401 pyrites, 435 argentiferous, 436 quality of, deposited by elec- trolysis, 145 refining, De'chaud and Gaul- tier's process, 396 refining by dynamo-electri- city, 403 refining by electricity, M. Thenard's experiments on, 404 refining by electrolysis, Dr. Higgs on, 406 refining by electrolysis, Mr. B. N. S. Keith on, 401 refining, electrolytic, in America, 421 refining, electrolytic at Biache, 419 refining, electrolytic, at Bi- mingham, 420 refining, electrolytic, cost or, 422 refining, electrolytic, at Ge- noa, 421 refining, electrolytic, at Ham- burg, 417 refining, electrolytic, Keith'b experiments in, 403 refining, electrolytic, Dr. Kiliani on, 406 refining, electrolytic, at Mar- seilles, 419 refining, electrolytic, at Oker, 420 ribbon, 417 rods, 242 rollers, 27 rollers, Wilde's process for producing, by el jctro-depo- sition, 143 Schlumberger's process for depositing 142 silicic, 514 olution, 92, 342 397 56* Copper, solution for experimental purposes, 92 solutions, specific resistance of, 5i5 solutions, working of, 155 sulphate of, 91, 397, 485 sulphate of, baths, Gramme's experiments with, 411 sulphate of, electrolysis of, 75 surfaces, oxidising, 500 voltaic etching of, 151 white, 503 wire, 239 pure, advantages of , 427 Copperas, 264, 397, 485 green, 340 Coppering cast-iron rollers, 144 cast-iron, 144 ,, cold solution for, 146 ,, notes, 154 ,, plants and sea-weed, 120 printing rollers, 141 process, Gulensohn's, 149 ,, Schlumberger's, 142 Weil's, 150 solution, 147 Dr. Eisner's, 148 Walenn's, 149 solutions, 147 alkaline, 147 steel shot, 154 wire, 146, 147 Copying animal substances, 116 coins and medals, 93 engraved metal plates and facing them with iron, 342 plaster busts, 112 medallions, 103 statues, &c., 140 vegetable substances, 120 Corner dishes, re-platiig, 259 Cornice poles, Ac., nickeling, 312 Corrosive acids, poisoning by, 511 ; , sublimate, 231 Corundum, 447 INDEX. Cost of electrolytic copper refining, 422 Counter-shaft, 308 Couronne des tasses, Volta's, 7 Cow-hair brushes, 455 Cowles' process of electric smelting, 444 Cowles' electric smelting furnace, 445 Cream ewers, gilding, 183, 211 Cream of tartar, 189, 231, 331 Crocus, 264, 327, 455 composition, 455 -. Crompton's dynamo, 36, 448 Crucible, Hessian, 463 platinum, 360 ,, porcelain, 360 Cruet stands, &c., plating, 244, 252 Cruickshank's trough battery, 9 Crysolite, 447 Crystalline deposit, 265, 540 graphite, 449 lead, 434, 525 silicon, 444 Crystallised double cyanide of gold, 462 silicon, 449 verdigris, 475 Cupreous oxide, 409 Cupric cyanide, 375 sulphides, 441 Cupriferous pyrites, 442 Current, direction of the, 471 electricity, i regulating amount of, 308 Cyanide, commercial, to determine strength of, 479 of copper, 372, 463 cupric, 375 dip, 287 excess of, 275 injurious, 216 free, 185, 223 test for, 499 of gold, 167, 461 of gold, double, crystallised 462 INDEX. 565 Cyanide, grey, 479 of mercury, 180 dip, 234 of platinum solution, 350 poisoning by, 510 of potassium, 142, 256, 345, 477, 478 of potassium, commercial, observations on, 221 of potassium, preparation of, 477 pure, 478 of silver, 225 solution of bismuth, 355 solutions, 221 solutions, old, recovery of gold and silver from, 461 sores, 511 of zinc, 372 Cyanogen, 479, 510 poisoning by, 510 DAMASCENING, 51 Daniell's battery, 8 cells, 177 Dead and bright gilding in parts, 205 gilding, 1 80 lustre, dip for, 237 nickel-plating, 327 ormoulu, 208 work, nickeling, 312 De"chaud and Gaultier's process for extracting copper, 396 Decomposition, electro-chemical, 358 of water, 72 Defects in gilding, causes of, 212 Definition of electrical terms, 82 De-gilding, 469 De-nickeling, 319 Density of alloys, 501 Dental work, nickeling, 323 Dentists' tools, &c., nickeling, 305 Deposit, crystalline, 265 Deposited metal, quantity of, 265 Depositing-bath (electrotyping), 132 Depositing copper upon glass, porce- lain, &c., 120 Depositing copper upon moulds, 342 silver by weight, 260 solid silver, 264 tank for tinning, 335 or vat, 281 tanks, 241 thick brass t 378 Deposition of alloys, 366, 534 aluminium, 360 aluminium, Goze's process, 363 aluminium, Jeancon's process, 363 ,, aluminium, Thomas andTilley's process, 362 antimony, 355 antimony by simple immersion, 357 bismuth, 355 brass, 366 bronze, 366 cadmium, 363 cadmium, Russell and Woolrich's process, 363 ., chromium, 364 chromium alloys, Sla- ter's process, 390 cobalt, 351 copper by dynamo- electricity, 139 copper on iron, 141 copper by single cell, evolution of hydrogen during, 393 of German silver, Morris and Johnson's pro- cess, 389 gold, 1 66 iron on copper, Klein's process, 341 iron, Jacobi and Klein's process, 342 lead, 357 566 INDEX. Deposition of magnesium, 365 magnesium and its alloys, 390 manganese, 365 manganium, 365 metals, electrical theo- ries in their relation to, 80 nickel, 280 platinum by battery current, 350 platinum, Boettger's solution for, 351 , , Thorn's process for de- positing, 513 ,, by simple immersion, 230 of tin, 331 , , tin by dipp ing, or sim- ple immersion, 331 ,, tin by single cell pro- cess, 334 zinc, 346, 515 De Ruolz's gold solution, 172 De-silvering, 253 Desmur's solution for nickeling small articles, 299 Dials, brass clock, &c., whitening, 231, 232 Didymium, 513 Different metals, brassing, 393 Dip, acid, 288 for bright lustre, 236 cyanide, 287 mercury, 234 nitric acid, 236 Dipping, 237 acid, 289, 481 deposition of tin by, 331 electro-brassed work, 387 gilding silver by, 164 Dips, acid, 236 or steeps, 287 Direction of current, 471 Dirty anodes, 278 Discovery of thermo-electricity, See- beck's, 39 Dishes, corner, replating, 259 Doctor, the, 184 Doctoring, 310, 311, 325 in gilding, 165 Dolly, finishing, 454 mop, 457 Dollying, composition for, 327 Double chloride of aluminium and sodium, 361 chloride of bismuth and am- monium, 355 chloride of magnesium and ammonium, 365 chloride of nickel and am- monium, 292, 298, 483 chloride of nickel and am- monium, solution of, 292 cyanide of gold and potas- sium, 167 cyanide of silver and potas- sium, 221 nickel salts, 483 salt of aluminium and po- tassium, 363 sulphate of cobalt and am- monia, 354 sulphate of cobalt and am- monium solution, 352 sulphate of nickel and am- monia, 283, 292, 296, 483 sulphite of silver solution, 231 Drawings, making electrotype plates from, 153 Driving belts, 487 Dropped articles, recovery of, from baths, 328 Dry colouring, 199 nickel-plating, 327 Dryer, centrifugal, 434 Ductility of metals, 499 Dust on the surface of the bath, 278 Dynamic force, 29 Dynamo-electric machine, 398 machine, Chutter's, 488 Dynamo-electric machine, Cromp- ton's, 36; at the Cowles' Works, 448 machine for elec- tric smelting, 448 machine, Giilcher's, 33 ,, machine, Mather's, 38 ,, machine, Schuc- kert's, 37 machine, Siemens', 30 machine, Weston's, 32 machines, 249 machines, manage- ment of, 491 Dynamo-electricity, 29 deposition of cop- per by, 139 nickel-plating by, 306 plating by, 249 refining copper by, 403 Dynamo-machines, advantages of gas-engines in driving, 491 ,, for deposition of copper, 145 ,, overheating, 493 moulding material, 97 Electric connection gripper, Hoe's, 130 Electric current, action of, upon compound substances, 74 dynamo, machines, 249 force, 29 magneto, machines, 249, 399 potential, 83 smelting, 443 smelting, Cowles' process, 444 INDEX. 567 Electric smelting furnace, Cowles', 448 spark, 22 Electrical connection, 100, 129 contact, 5 current, 83 energy, 4 resistance, 83 terms, definition of, 82 theories in their relation to the deposition of metals, 80 transfer of elements, 77 units, 87 Electricity, chemical, 2 current, i dynamo, 29 dynamo, deposition of copper by, 139 dynamo, nickel - plating by, 306 dynamo, nickel - plating small articles by, 326 dynamo, plating by, 249 dynamo, refining copper by, 403 magneto, 21 negative 2 positive, 2 quantity of, and electro- motive force, 490 refining copper by, M. Th6nard's experiments in, 404 voltaic, historical review of, i Electro-brassed work, bronzing, 384 dipping, 387 lacquering, 387 zinc work, French method of bronz- ing, 386 Electro-brassing cast-iron work, 379 lead, pewter, and tin work, 381 notes on, 392 observations on, 382 568 INDEX. Electro-brassing wrought-iron work, Electro-deposition of nickel, 280 380 palladium, 354 zinc work, 380 platinum, 348 Electro bronzes, 192 platinum, chemical action, 4 Thorn's pro- chemical action, Faraday's cess, 513 nomenclature of, 70 platinum, Bo- chemical decomposition, 358 ettger's solu- chlorination of gold ores, tion, 351 Cassel's process, 438 platinum by coppering flowers, insects, simple immer- &c., 118 sion, 350 deposited gold, colour of, 196 silicon, 365 silver, thickness of, 265 silver, 219 Electro-deposition of alloys, 366, 379, tin, 331 534 5, various metals, aluminium and 348 its alloys, 360, zinc, Watt's so- 5i3 lution for, 345 antimony, 355 Electro-etching, 151 auxiliary ope- composition of bath rations, 466 for, 152 bismuth, 355 Electro-gilding, general manipula- brass, 366 tions of, 177 bronze, 366, 388 or gilding by direct ? , cadmium, 363 current, 166 chromium, 364, ,, solutions, cold, 172 390 zinc articles, 192 cobalt, 351, 517 Electro-gilt work, burnishing, 460 copper, 91 Electro-magnetism, 18 German silver, Electro-magnets, 21 388 Electro-metallurgy, 61, 395 }> German silver of copper, Dr. C. Morris and W. Siemens Johnson's pro- on, 401 cess, 389 zinc, 439 w historical re- Le- view of, 51 trange's pro- iron and zinc, cess, 439 340, 531 zinc,Luckow's lead, 357, 525 process, 441 magnesium,365 zinc, MM.Blas manganese, 365 and Heist's . manganium, process, 442 365 ,, Werdermann's materials used process, 443 in, 475 Electromotive force, 28, 82, 399 INDEX. Electromotive force of batteries, 88 Electro-negative elements, 89 Electro-nickeling bar fittings, &c., 31 1 ., bicycles, 313 spokes of, bits, spurs, &c., 308 book-clasps, &c., 322 brass and copper articles, 306 cast-brass work, 330 cast-iron work, 317 chain work, 318 cheap fancy work, 306 cornice poles, &c., 312 dead work, 312 dental work, 323 forceps, &c., 323 gauze wire, 321 handrails, &c., 312 harness furniture, 316 long pieces of work^ 312 mullers,&c., 309 printing-rollers, 321 purse mounts, &c , 3?2 railway keys, &c., 326 sanitary work, 311 sausage-warmers, 309 second-hand bicy- cles, 314 ships' deck lamps, 312, 327 shop fronts, 312 small screws, 326 steel, 306, 322 stirrups, 317 stove fronts, die., 313 sword - scabbards, 3i5 table lamps, &c.,3o8 569 Electro-plate, 251 characteristics of, 259 resilvering, 258 Electro-plated articles, whiten ing, 267 articles, stripping silver from, 259 Electro-plating, 219 bath, arrangement of, 241 battery, 242 brass, &c., 250 Britannia metal, &c., 250 cruet stands, Ac., 244, 252 German silver, &c., 250 liqueur stands, &c.> 245 pewter, tin, &c., 250 spoon and fork work, 238, 244 ,, tea and coffee ser- vices, 246 zinc, iron, &c., 250 Electro-polar, 16 positive elements, 89 Electro-silvering pewter solder, 277 Electro-soldering, 276 of copper, Eisner's experiments, 472 Electro-tinned articles, replating, 260 Electro-tinning brass pins, 331 Fearn's process, 336 Roseleur's solution for, 336 sheet iron, 338 sheet iron, Spence's process, 338 Steele's process, 337 Electrode, 71 carbon, 171 Electrodes, 72 Electrography, 64 Electrolysis, Dr. Higgs on refining copper by, 406 INDEX. Electrolysis, Mr. B. N. S. Keith on refining copper by, 401 ,, of lead salts, 525 ,, recovery of tin from tin ' scrap by, 338, 521 , , of sulphate of copper, 75 ,, theory of, 70 Electrolyte, 71, 408 Electrolytes, 71 Electrolytic classification of elements, 89 Electrolytic copper, 145 refining in Ame- rica, 421 refining at Bia- che, 419 refining at Bir- mingham, 420 refining, cost of, 422 refining at Ham- burg, 417 refining at Mar- seilles, 419 refining at Oker, 420 tensile strength of, 145 Electrolytic extraction of copper from ores, Marchese's process, 437 Electrolytic refining, arrangement of baths for, 427 refining of copper, Dr. Kiliani on, 406 refining of copper by separate current, 397 refining of lead, Keith's process, 428, 429 refining plant, arrange- ment of, 399 refining, progress of, 416 soldering, 472 theory, practical illustra- tion of, 77 treatment of copper in Genoa, 421, Electrolytic treatment of natural sul- phides, 441 treatment of ores, 434 treatment of zinc ores, Electros, 138 Electroscope, 3 Electrotype, 9 blocks, 136 bronzing the, 101 finishing the, 134 mould, 264 press for, 127 process, Spencer's paper on, 54 rollers for impressing leather, 144 thickness of an, 156 tinning and backing the, treatment of, 101, 133 Electrotypes, nickel-facing, 320 Electrotyping, Adams' process for metallising the moulds for, 131 Electrotyping, arrangement of bat- tery for, no book-work, 135 building iron for, 126 case-filling and steam - heating tables, for 126 colossal statues, y, 331 tinning iron arti- cles by, 331 tinning zinc by, 332 whitening articles by, 230 Impure gold, employment of, 209 India-rubber tubing, 237 Indicator, speed, 249, 497 Induced currents, 30 magnetism, 21 Inductors, 24 Insides of plated articles, stripping gold from, 256 of vessels, gilding, 183 INDEX. Insulating brackets, 306 Insulators and conductors, 80 Intensity armature, 25 relative, of batteries, 495 Internal resistance, 85 Iodide of potassium, 224 Iodine, 513 Iridium, 501, 513 Iron, 501, 513 ammonio-sulphate solution of, 344, 532 anodes, 341, 397 articles, tinning, by simple im- mersion, 331 battery, Callan's, n cast, dogs, bronzing, 387 pickling bath for, 290 work, preparing for zinc- ing, 346 depositing, upon moulds, 342 deposition of, Jacobi and Klein's process, 342 electro-deposition of, 340, 532 fenders, bronzing, 387 ferrocyanide of, Boettger's solu- tion of, 344 galvanising, 345 nickeling, 317 oxide of, 327, 380 perchloride of, 255, 264 solution of, 507 peroxide of, 26 rough cast, brass solution for, 377 sesquioxide of, 396 solution, Klein's, 342 solution for coating copper plates with, 508 steel, zinc, &c., stripping silver from, 468 sulphate of, 93, 344, 396 sulphate of, and chloride of am- monium solution, 344 sulphate of peroxide of, 435 sulphide of, 136, 435 ., tanks, 277 577 Iron wire anodes, 343 Heeren's method of tin- ning* 334 work, electro-brassing, 379 scouring, 380 wrought, electro-brassing, 380 wrought, work, preparing for zincing, 346 and zinc, electro-depositio 340 zinc, Ac., plating, 250 Isonandra gutta, 94 TACOBFS discovery, announcement d of, 52 Jacobi and Klein's process, 342 Jeancon's aluminium process, 363 Jewellers' rouge, 271, 457, 471 Jewellery articles, gilding, 208 ,, cheap, French gilding for, 160 ,, cheap, gilding, 212 ,, coloured, 199 ,, French, gilding, 212 Jointing belts, 488 Jordan's discovery, Dircks on, 59 ,, process, 53 of TT'EEPER, 22 Keeping up the strength baths, 393 Keith's experiments in refining cop- per by electrolysis, 403 ,, process for electrolytic refin- ing of lead, 428 Kiliani. Dr., on electrolytic refining of copper, 406 Klein's process for depositing iron, 34i Knight's plumbagoing process, 129 Kobalts, 352 Kobel, 352 T AC carmine, 385 Lacquering electro-brassed work, 387 578 INDEX. Lambert's process for treating gold and silver ores, 437 Lamp-posts, coppering, 145 Lamps, table, 131 copper, making by electroly- sis, 153 depositing iron upon, 342 elastic, 112 floating, 118 from fusible metal, 108 gutta-percha, 264 metallising the, 130 of sealing-wax, 103 plaster, electrotyping from, 136 plaster of Paris, 98, 115 Mounts, lead, 254 silver, 254 umbrella, &c., nickeling, 306 suspending, 327 Mugs, gilding, 183 Mullers, silver or plated work. 455 steel, 455 >, tools, 452 Porcelain, coating with copper, 120 Porous cell, u, 63 ,, origin of, 63 Positive electricity, 2 pole, 71, 241 Pot gilding, 162 metal, 503 Potash, American, 235, 286, 476 ,, bath, 179, 235 bath, for nickel-plating, 286 M bichromate of, 15 ,, carbonate of, 101, 221, 476 ,, caustic, 287, 476 ,, monosilicate of. 287, 365 ,, nitrate of, 253 and soda alums, 332 , , sulphate of, electrolysis of, 76 ,, yellow prussiate of, 227, 344, 481 Potassa, bitart-rate of, 189, 230 pyrophosphate of, 160 ,, stannateof, 372 ,, zincate of, 372 Potassic tartrate of antimony, 356 Potassium, 513 M cyanate of, 478 cyanide of, 142, 256, 345, 477 M cyanide of, commercial, observations on, 221 ,, cyanide of, to determine the strength of, 479 ,, cyanide of, preparation of, 477 ,, cyanide of, pure, 478 i> ferrate of, 341 n ferrocyanide of, 168, 344, 477. 48i M iodide of, 224 M sulphide of, 140, 292 INDEX. 5*7 Potassium, sulphide of, oxidising with, 270 Potts' process for nickel-plating, 296 Powder, bleaching, 274, 392 emery, 455 putty, 459 sienna, 385 tin, for electrotyping, 138 Powdered crocus, 455 ,, plumbago, 270 ,, pumice, 303 Powders, bronze, 386 Powell's process for nickel-plating, 296 Power planing and sawing machine, 136 relative, of batteries, 494 Precautions in moulding, 100 to be observed when fill- ing the bath with work, 274 Precipitation of gold, 176 ,, of silver, 222 of silver from old baths, 465 Preparation of chloride of gold, 157 of chloride of platinum, 349 of cyanide of potassium, 477 of gilding solutions, 167 of the mould in electro- typing, 125 of new work for plating, 233 of nickel solutions, 283, 291 of nitrate of silver, 219 of old plated ware for resilvering, 251 of silver solutions, 221 of steel articles for gild- ing, 187 of watch parts for gild- ing, 1 88 of the work for burnish- ing, 459 Preparation of the work for gilding, 164, 179 of work for nickel-plat- ing, 301 of zinc castings for gild- ing, 192 Prepared chalk, 231 Preparing cast-iron work for zincing, 346 the formes, 124 the mould, for electrotyp- ing, 104 the tools for burnishing, 458 wrought - iron work for zincing, 346 Prince's metal, 503 Printers' set-up type, electrotyping, 123 Printing rollers, coppering, 141 rollers, producing, by elec- tricity, Wilde's process, 143 rollers, nickeling, 321 Process, Adams', for metallising moulds, 131 ,, Adams', Dr., for nickel- plating, 292 ,, autogenous, 281 ,, battery, making gilding solution by, 171 ,, Becquercl's, for treatment of ores, 434 ,, Bias and Heist's zinc, 442 ,, brassing, Morris and John- son's, 372 ,, brassing, Russell and Wool- rich's, 372 ,, brassing, Wood's, 372 ,, Cassel's, for electro-chlori- nation of gold ores, 438 ,, for coating non-conducting surfaces, 156 ,, Cowles' electric smelting, 444 Dechaud and Gaultier's, for refining copper by elec- trolysis, 396 5S3 INDEX. Process for deposition of tin by single cell, 334 electrotype, Spencer's paper on, 54 Eisner's oxidising, 271 Fearn's tinning, 336 Goze's, for deposition of aluminium, 363 ,, Gulensohn's, coppering, 149 ,, Hermann's zinc, 347 ,, Jacob! and Klein's iron, 342 Jeancon's, for deposition of aluminium, 363 ,, Jordan's, electrotyping, 53 Keith's, for refining lead, 428 ,, Klein's, for depositing iron upon copper, 341 Lambert's, for treating gold and silver ores, 437 ,, Lenoir's electrotyping, 140 ,, Letrange's zinc, 439 Luckow's zinc, 441 Marchese's, for electrolytic extraction of copper from ores, 437 ,, Person and Sire's brassing, 378 ,, plumbagoing, 129 ,, ,, Knight's, 129 Potts' nickel, 296 ,, Powell's, for nickel-plating, 296 ,, of refining copper by elec- trolysis, Elkington's, 400 ,, Kussell and Woolrich's, for deposition of cadmium, 363 Schlumberger's, for deposit- ing copper, 142 Slater's, for deposition of chromium alloys, 390 ,, Spence's, for electro-tinning sheet iron, 338 ,, Steele's, for gilding by con- tact with zinc, 164 Process, Steele's, tinning, 337 ,, Thomas and Tilley's, for deposition of aluminium, 362 ,, Unwinds, for nickel-plating, 394 ,, Wahl's, for oxidising, 271 ,, Watt's, for the electro-de- position of zinc, 345 ,, Weil's coppering, 150 ,, Weston's, for nickel-plat- ing, 295 ,, wet-colouring, 200 ,, French, 201 ,, ,, London, 201 ,, wet, of smelting, 401 ,, Wilde's, for producing printing rollers by mag- neto-electricity, 143 ,, zinc, Werdermann's, 443 Processes, brassing, Brunei, Bisson, and Co.'s, 369 ,, brassing, Newton's, 371 ,, ,, Roseleur's, ,, ,, Salzede's, 371 . i ,, Walenn's, 374 ,, colouring, 198 Progress of electrolytic refining, 416, 4i7 Protochloride of tin, 331 Protoxide of chromium, 365 Prussian blue, 385, 485 Prussiate of potash, yellow, 227, 477, 481 Prussic acid, 227, 481 Pulleys and belts, accumulation of lumps on, 488 ,, belts coming off from, 488 Pumice, 258, 303 ,, powder, 181 ,, stone, 257 Pure copper anodes, 399 ,, cyanide, 478 Purple of Cassius, 463 Putty powder, 459 * Pyrites, auriferous, 439 copper, 435 cupriferous, 442 INDEX. 539 Pyrites, martial, 442 Pyro-gilding, 196 Pyroligneous acid, 476 Pyrophosphate of potassa, 160 ,, silver, 484 ,, soda, 161, 484 ,, sodium, 296 ,, tin bath, 334 Pyro-plating, 266 ,, with aluminium, 266 ,, with gold and silver, 266 ,, with platinum, 266 Pyroxylic spirit, 93 AUALITY, active, of cyanide of ^ potassium, 221 Quantity, 83, 86 ,, armature, 25 ,, of electricity and electro- motive force, 490 ,, of metal deposited, 265 Queen's metal, 503 Quicking, 132 ,, solutions,. 234 Quicklime, 454 Quicksilver, 233, 482 "DAG, gilding with the, 165 Railway keys, &c., nickeling, 326 Re-colouring gold articles, 199 Record's gilding bath, 176 Recovery of dropped articles from the bath, 328 gold and silver from scratch - brush waste, 464 gold and silver from old stripping solu- tions, 465 gold from old cyanide solutions, 461 nickel from old solu- tions, 324 silver from old cyanide solutions, 462 tin from tin scrap by electrolysis, 338 Ted brass, 503 gold, 197 ochre, 207, 271 ormoulu, 207 oxide of mercury, 234 precipitate, 234 Bedding, 264 Refining copper by dynamo-electri- city, 403 by electricity, M. Thenard's expe- riments on, 404 by electrolysis, De- chaud and Gaul- lier's process, 396 ,, ,, by electrolysis, El- kington's process, 400 .1 ,i by electrolysis, Dr. Higgson, 406 by electrolysis, Mr. B. N. S. Keith on, 401 ,, electrolytic, of copper in America, 421 ,, electrolytic, arrangements of baths for, 427 ,, electrolytic, of copper at Biache, 419 ,, electrolytic, of copper at Birmingham, 420 ,, electrolytic, of copper, cost of, 422 ,, electrolytic, of copper at Hamburg, 417 ,, electrolytic, of copper, Keith's table of experi- ments on, 403 _,, copper, electrolytic, Dr. Kiliani on, 406 copper, electrolytic, at Marseilles, 419 copper.electrolytic.atOker, 420 ,, copper, electrolytic pro gress of, 416 electrolytic, of copper by separate current, 397 590 INDEX. Refining lead by electrolysis, Keith's process, 428 plant, electrolytic, arrange- ment of, 399 Regulating amount of current, 308 Regulus, copper, 404, 437 Relative conducting power of metals, 82 ,, conductivity of metals, 514 ,, intensity of batteries, 495 power of batteries, 494 Remedies and antidotes in cases of poisoning, 509 Removing the forme, 127 gas bubbles, 322 soft solder from gold and silver work, 507 tin from tin scrap, 521 Re-nickeling American cheap goods, German cheap goods, ,, French cheap work, old work, 319 Re-plating corner dishes, 259 electro-tinned articles, 260 old work, 251 preparation of old plated ware for, 251 Residuary magnetism, 30 Re-silvering electro-plate, 258 ,, old work, 251 Resin, 471 Resistance, 399 coil, 275, 308, 495 coils, 284 Ohm's law, 85 specific, of solutions of copper, 515 Rheostat, 542 Rhodium, 513 Ribbon, copper, 417 Rings, gilding, 177, 179 Nobili's, 359 Rock alum, 362 Rods, anode, 308 ,, brass, 242 Rods, conducting, 242, 308 ,, copper, 242 ,, leading, 308 ,, suspending, 274, 308 M cleaning, 276 Rolled cobalt anodes, 352 nickel, 284 anodes, 329, 482 silver anodes, 274 Rollers, punting, nickeling, 321 Roseleur's argyrometric scale, 262 brassing processes, 373 tinning solutions, 333, 336 Rottenstone, 257, 303, 456 Rouge, jewellers', 271, 454> 47 1 Kough sanding, 452 Roughing, 452 Rubidium, 513 Russell and "Woolrich's brassing pro- cess, 372 and Woolrich's process for deposition of cadmium, 363 . Ruthenium, 513 CAL ammoniac, 91, 198, 299/484 ^ Salamstein, 449 Salt, bronzing, 357 common, 291 in nickel baths, 325 Glauber's, 225 ,, spirit of, 482 of Tartar, 224, 476 tin, 390 tinning, 477, 506 Saltpetre, 165, 199 Chili, 467 Salts, cobalt, 351 ,, colouring, 162 of lead, 428 nickel, 283, 483 ,, simple method of pre- paring, 298 Sand, glass-cutters', 452,486 old, 452 Trent, 315,452,486 holes, 154, 330 Sanding, 452 rough, 452 INDEX. 591 Sanitary work, &c., nickeling, 311 Satin finish (oxidising), 271 Sawdust, boxwood, 187, 267 Saw table, 134 Saxton's magneto-electric machine, 23 Scabbards, sword, gilding, 185 nickeling, 3 15 Scheele's prussic acid, 481 Schlumberger's coppering process, 142 Schuckert's dynamo-electric machine, 37 Scouring brushes, 245 cast-iron work, 380 ,, tray for nickel work, 301 work fcr nickel-plating, 303 Scratch-brush, 178, 179 lathe, 248 ,, waste, extraction of gold and silver from, 464 Scratch-brushes, 248 brushing, 247 with soap suds, 179 spoons and forks 248 with stale beer, 179 with vinegar, 187 Screws, binding, 498 &c., nickeling, 305 small, nickeling, 326 wiring, 305, 327 Sea salt, 441 Sealing-wax, 96, 471 moulds of, 103 solution of, 147 Seals and crests, copying, 96 Secondary batteries, 16 Section of Clamond's thermo-pile, 47 Seebeck's discovery of thermo-electri- city, 39 Selenium, 513 Separate battery, electrotyping by, no ;s current, electrolytic refining of copper by, 397 Sesquioxide of chromium, 365 iron, 396 copper, 145 Sheffield lime, 315, 454, 485 plate, 251 Ship plate, 259 Ships' deck lamps, nickeling, 313 Shop fronts, nickeling, 312 Shot metal, 503 Siemens' discovery of dynamo-elec- tricity, 29 dynamo-electric machine, . 30 Dr. C. W., on the electro- metallurgy of copper. 401 Sienna powder, 385 Silica, 360, 447 Silicic copper, 514 Silicious brass, 514 Silicium, 365 bronze, telephonic, 514 Silico-aluniinium bronze, 449 Silicon, 513 bronze, 444 bronzes, 449 crystalline, 444 crystallised, 449 deposition of, 365 Silk and cotton, gilding, 195 Silver, 219, 501 ,, aluminium, 448 ,, anode, 2.21 ,, anodes, 241 ,, brightening solution, 229 ,, carbonate of, 224 ,, chloride of, 220, 231, 463 ,, cold stripping solution for, 468 ,, cyanide of, 225 ,, ,, solutions, 221 ,, depositing, by weight, 260 ,, electro-deposition of, 219 extraction of, by the dry method, 464 extraction of, by the wet method, 463 ,, filigree work, gilding, 184 59 2 INDEX. Silver filigree work, gilding solu- tion for, 185 ,, foil, 189, 508 ,, ,, platinising, 507 ,, German, 388 ,, anode, 389 ,, ,, electro - deposition of, 338 ,, gilding, 186, 213 ,, solution, 388 ,, gilding, by simple immersion, 164 ,, and gold alloys, deposition of, 390 ,, and gold, recovery of, from scratch-brush waste, 464 ,, and gold, recovery of, from old stripping solutions, 465 and gold work, to remove soft solder from, 507 ,, grain, 219 ,, hyposulphite of, 227 ,, imitation antique, 269 ,, mounts, 254 ,, nielled, 273 , nitrate of, 219,390 ,, ores, chlorination of, 435 ,, oxide of, 224, 227 ,, oxidised, 269, 472 ,, oxidising, 269 ,, pink tint upon, 274 or plated work, burnishing, 459 or plated work, polishing, 455 platinised, 132 ,, and platinum, alloy of, 391 ,. i. anode, 391 ,, and potassium, double cya- nide of, 221 ,, powder, 190 ,, preparation of nitrate of, 219 pyrophosphate of, 484 ,. recovery of, from old cya- nide solutions, 462 ,, sand, 181 Silver, solid deposits of, 264 ,, solution, 342 ,, double sulphite of, 231 for gilding, 159 ,, ,, Tuck's, 225 ,, solutions, 221 ,, ,, preparation of, 221 standard, 503 ,, stripping by battery, 468 ,, ,, from iron, steel, zinc, &c., 468 from old-plated ar- ticles, 252 ,, ,, solution for, 467 ,, sulphate of, 225 ,, sulphide of, 227 ,, sulphuring, 272 ,, thickness of electro deposi- ted, 265 ,, and tin alloy, deposition of, 389 ,, and tin solution of, 389 ,, work, stripping gold from, 469 ,, work, whitening, 267 Silver-plating bath, preparation of new work for, 233 ,, battery, 242 ,, brass, &c., 250 ,, bright, solution for, 228 , Britannia metal, &c., 250 ,, cruet stands, &c., 244, 252 by dynamo-electricity, 249 ,, German silver, &c., 250 liqueur stands, &c., 245. 252 pewter, tin, &c., 250 spoon and fork work, 238 ,, tea and coffee ser- vices, 246 ,, zinc, iron, &c., 250 INDEX. 593 Silvering, arrangement of bath for, 241 bath, preparation of new work for, 233 brass clock dials, &c., 231 ; , bright, solution for, 228 j. notes, 274 ., re-, preparation of old plated ware for, 251 thermometer, &c., scales, 232 Silveroid, 391 Simple arrangement for gilding small articles, 177 ., and compound voltaic cir- cles, 84 ., immersion, deposition by, 230 ,, immersion, deposition of an- timony by, 357 ,, immersion, deposition of platinum by, 350 immersion, deposition of tin by, 331 j *v immersion, gilding silver by, 159 - immersion, tinning iron arti- cles by, 331 ., immersion, tinning zinc by, 332 ,, immersion, whitening arti- cles by, 230 ,, voltaic circle, 4 Single cell process, deposition of tin by, 334 ,, electrotyping by, 88 Single nickel salts, 483 Slaked lime, 303 Slate tanks, 241 Slater's process for deposition of chromium alloys, 390 Slinging wire, 179, 239 wires, 215 old, 278 Slipping of belts, 493 Small articles, oxidising, 271 battery for gilding, 177 brass and copper articles, nic- keling, 306 Small steel articles, nickeling, 305 Smee battery, 9. 181 Smelting, electric, 443 i. furnace, Cowles', 448 wet process of, 401 Snuff boxes, gilding, 165 Soap-suds, scratch-brushing with, 178, 179 used in burnishing, *59 Soda, antiuioniate of, 430 arsenite of, 430 bisulphite of, 194, 231, 374 caustic, 332 ,, nitrate of, 252 ,, phosphate of, 191 pyrophosphate of, 161, 484 sulphate of, 225 Sodium, 513 bisulphite of, 231, 272 chloride of, 186, 292, 326 pyrophosphate of, 296 ,, sulphide of, 292, 300 Soft solder, 503 to remove from gold and silver work, 507 Soft soldering, 505 Solder, brass, 504 ,, hard, 503 ,, pewter, 259 ,, soft, 503 Soldering, 504 ,, electro, 276 electro, of copper, Eisner's experiments in, 472 electrolytic, 472 hard, 504 liquid, 507 soft, 505 Solid silver deposits, 264 Solution, Bacco's brassing, 376 Beardslee's cobalt, 353 Becquerel's cobalt, 353 gold, 168 for metallo- chromy, 359 Boettger's cobalt, 354 594 INDEX. Solution, Boettger's, for depositing platinum, 351 ferrocyanide of iron, 344 brass, prepared by battery, 378 brassing, Dr. Heeren's, 373 ,, Morris and John- son's, 372 Russell and Wool- rich's, 372 Wood's, 372 ,, brightening, 229, 276 bronzing, 388 cold, for electro-gilding, 172 stripping, 253 ,, stripping, for silver, 468 concentrated brass, 393 ,, platinum, 349 coppering, Walenn's, 149 ,, De Briant's gold, 169 Desmur's for nickeling small articles, 299 ,, De Ruolz's gold, 172 ,, double chloride of nickel and ammonium, 292 ,, double cyanide of nickel, and potassium, 297 ,, double sulphate of cobalt and ammonia, 354 ,, double sulphate of nickel and ammonium, 299 double sulphite of silver and sodium, 231 Eisner's, Dr., coppering, 148 ., ethereal, of gold, 159 ,, Fizeau's gold, 169 ., German silver, 388 gilding, ferrocyanide, 175 ,, gilding, preparation of, 167 gilding, preparation of, by battery process, 171 ,, for gilding silver, 159 for gilding silver filigree work, 185 Solution, gold, for producing a dead or matted surface, 215 ., gold, for a stout coating, 215 Hillier's, Dr., for tinning metals, 334 ,, mercurial, 189, 203 ,, nickel, preparation of, 283 for nickeling tin, Ac., 298 ,, Parkes', plating, 224 Person and Sire's zincing, 346 of phosphorus, 485 of platinum, oxidising with, 270 Potts' nickel, 297 Powell's nickel-plating, 296 Record's gilding, 176 Roseleur's tinning, 333 336, stripping, for gold, 469 stripping, for nickel, 319, 470 ,, stripping, for silver, 467 ,, for stripping silver by battery, 468 ,, of tin and silver, 389 for tinning iron articles by simple immersion, 331 ,, Tuck's plating, 225 ,, Watt's, for deposition of zinc, 345 ,, Watt's gilding, 176 ,, Weil's, tinning, 334 ,, Winckler's brassing, 376 ,, Wood's gilding, 169 whitening, 332 Solutions, aluminium, 362 ,, antimonj 7 , 355, 356 ,, brassing, 367, 368 ,, bronzing, 371 cobalt, 353, 520 ,, copper, specific resistance of, 5i5 copper, working of, 155 coppering, 147 ., ,, alkaline, 147 cyanide, 462 INDEX. 595 Solutions, old cyanide, recovery of silver from, 462 gilding, 215 preparation of, 167 treatment of, 208 old gold, 210 gold, strengthening, 173 ,, hot brassing, 394 nickel, common salt in, 325 ,, nickeling, preparation of, 291 plating, 221 quicking, 234 ,, recovery of nickel from old, 324 ,, silver, preparation of, 221 stripping, 466 stripping, recovery of gold and silver from, 465 for tinning, 332 Walenn's brassing, 374 waste, &c., recovery of gold and silver from, 461 zincing, 346 Sores, cyanide, 511 Specific resistance of solutions of copper, 515 Speculum metal, 503 Speed indicator, 249, 497 Spence's process for electro-tinning sheet iron, 338 Spencer's paper on the electrotype process, 54 Spermaceti, 96 Spirit, methylated, 384 ,, of salt, 482 of turpentine, 270 ,, of wine, 274 Spokes, bicycle, nickeling, 313 Spoon and fork plating, 238, 244 Spoons and forks, scratch-brushing, 248 stripping, 467 gilding, 165 Spurious gold, 213 Spurs, bits, &c., nickeling, 308, 316 Standard gold, 503 silver, 503 Stannate of potassa, 372 Statues, &c., copying, 140 Statuettes, oxidising, 271 Steam-heating table, 126 Stearic acid, 96 Stearine, 96 Steel anode, 341 ,, articles, nickeling, 305, 322 ,, ,, preparation of for gild- ing, 187 bronze, 386 ,, burnishers, 458 ,, facing, 340 ,, ,, copper-plates, 508 ,, gilding, 186 ,, iron, zinc, : " No word having connection with any branch of constructive engineering seems to be omitted. 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" We confidently recommend all interested in heating by hot water to secure a copy of this valuable little treatise." The Plumber and Decorator. MECHANICAL ENGINEERING, etc. Steam Engine. TEXT-BOOK ON THE STEAM ENGINE. With a Sup- plement on Gas Engines, and PART II. ON HEAT ENGINES. By T. M. GOODEVE, M.A., Barnster-at-Law, Professor 01 Mechanics at the Normal School of Science and the Royal School of Mines; Author of "The Princi- ples of Mechanics," "The Elements ot Mechanism," &c. Eleventh Edition, Enlarged. With numerous Illustrations. Crown 8vo, 6s. cloth. [Just published. "Professor Goodeve has given us a treatise on the steam engine which will bear comparison with anything- written by Huxley or Maxwell, and we can award it no higher praise." Engineer. " Mr. Goodeve's text-book is a work of which every young engineer should possess himself. 1 Mining Journal. "Essentially practical in its aim. The manner of exposition leaves nothing to be desired." Scotsman. Gas Engines. ON GAS-ENGINES. Being a Reprint, with some Additions, of the Supplement to the Text-book on the Steam Engine, by T. M. GOODEVE, M.A. Crown 8vo, zs. 6d. cloth. " Like all Mr. Goodeve's writings, the present is no exception In point of general excellence It is a valuable little volume." Mechanical World. Steam. THE SAFE USE OF STEAM. Containing Rules for Un- professional Steam-users. By an ENGINEER. Sixth Edition. Sewed, 6d. " If steam-users would but learn this little book by heart boiler explosions would become sensations by their rarity." English. Mechanic. Office JBooJefor Mechanical Engineers. THE MECHANICAL ENGINEER'S REFERENCE BOOK, for Machine and Boiler Construction. In Two Parts. Part I. GENERAL ENGINEERING DATA. Part II. BOILER CONSTRUCTION. With 48 Plates and numerous Illustrations. By NELSON FOLEV, M.I.N.A. Folio, half-bound. Price 3 55. [Nearly ready. Coal and Speed Tables. A POCKET BOOK OF COAL AND SPEED TABLES, for Engineers and Steam-users. By NELSON FOLEY, Author of " Boiler Con- struction." Pocket-size, 35. 6d. cloth ; 45. leather. "These tables are designed to meet the requirements of every-day use ; they are of sufficlint scope for most practical purposes, and may be commended to engineers and users of stean.." Iron. "This pocket-book well merits the attention of the practical engineer. Mr. Foley has com- piled a very useful set of tables, the information contained in which is frequently required by engineers, coal consumers and users of steam." Iron and Coal Trades Review. Fire Engineering. FIRES, FIRE-ENGINES, AND FIRE-BRIGADES. With a History of Fire-Engines, their Construction, Use, and Management ; Re- marks on Fire-Proof Buildings, and the Preservation of Life from Fire ; Statistics of the Fire Appliances in English Towns ; Foreign Fire Systems ; Hints on Fire Brigades, &c. &c. By CHARLES F. T. YOUNG, C.E. With numerous Illustrations, 544 pp., demy 8vo, i 45. cloth. ' " To such of our readers as are interested in the subject of fires and fire apparatus, we can most heartily commend this book. It is really the only English work we now have upon the subject." Engineering. "It displays much evidence of careful research; and Mr. Young has put his facts neatly together. It is evident enough that his acquaintance with the practical details of the construction of steam fire engines, old and new, and the conditions with which it is necessary they should comply, Is accurate and full." Engineer. Estimating for Engineering Work, SON'S CATALOGUE. MR. HUMBER'S GREAT WORK ON MODERN ENGINEERING. Complete in Four Volumes, imperial 4to, price 12 i2s., half-morocco. Each Volume sold separately as follows : A RECORD OF THE PROGRESS OF MODERN ENGINEER- ING, FIRST SERIES. Comprising Civil, Mechanical, Marine, Hydraulic, Railway, Bridge, and other Engineering Works, &c. By WILLIAM HUMBER, A-M.Inst.C.E., &c. Imp. 4to, with 36 Double Plates, drawn to a large scale, Photographic Portrait of John Hawkshaw, C.E., F.R.S., &c., and copious descriptive Letterpress, Specifications, &c., 3 35. half-morocco. List of the Plates and Diagrams. Thames, West London Extension Railway (5 plates) ; Armour Plates : Suspension Bridge, Thames (4 plates) ; The Allen Engine ; Sus- pension Bridge, Avon (3 plates) ; Underground lway (3 plates). Victoria Station and Roof, L. B. & S. C. R. (8 plates) ; Southport Pier (2 plates) ; Victoria Station and Root, L. C. & D. and G. W. R. (6 plates); Roof of Cremorne Music Hall ; Bridge over G. N. Railway ; Roof of Station, Dutch Rhenish Rail (a plates) ; Bridge over the " Handsomely lithographed and printed. It will find favour with many who desire to preserve In a permanent form copies of the plans and specifications prepared for the guidance of the con- tractors for many important engineering works." Engineer. HUMBERTS RECORD OF MODERN ENGINEERING. SECOND SERIES. Imp. 4to, with 36 Double Plates, Photographic Portrait of Robert Stephensqn, C.E., M.P., F.R.S., &c., and copious descriptive Letterpress, Specifications, &c., 3 35. half-morocco. List of the Plates and Diagrams. Birkenhead Docks, Low Water Basin (15 plates) ; Charing Cross Station Roof, C. C. Railway (3 plates); Digswell Viaduct, Great Northern Railway ; Robbery Wood Viaduct, Great Northern Railway ; Iron Permanent Way; Clydach Viaduct, Merthyr, Tredegar, and Abergavenny Railway ; Ebbw Vladnct, Merthyr, Tredegar, and Abergavenny Rail- way ; College Wood Viaduct, Cornwall Rail- way ; Dublin ^Vinter Palace Roof (3 plates) ; Bridge over the Thames, L. C. & D. Railway (6 plates) ; Albert Harbour, Greenock (4 plates). " Mr. Humber has done the profession good and true service, by the fine collection of examples he has here brought before the profession and the public." Practical Mechanic's yournal. HUMBER'S RECORD OF MODERN ENGINEERING. THIRD SERIES. Imp. 4to, with 40 Double Plates, Photographic Portrait of J. R. M'Clean, late Pres. Inst. C.E., and copious descriptive Letterpress, Speci- fications, &c., 3 35. half-morocco. List of the Plates and Diagrams. Sewer, Reservoir and Outlet (4 plates) ; Outfall Sewer, Filth Hoist ; Sections of Sewers (North and South Sides). THAMES EMBANKMENT. Section of River Wall ; Steamboat Pier, Westminster (2 plates): Landing Stairs between Charing Cross ana Waterloo Bridges ; York Gate (2 plates) ; Over- flow and Outlet at Savoy Street Sewer (3 plates) ; MAIN DRAINAGE, METROPOLIS. North Side. Map showing Interception of Sewers ; Middle Level Sewer (2 plates) ; Outfall Sewer, Bridge over River Lea (3 plates) ; Outfall Sewer, Bridge over Marsh Lane, North Woolwich Railway, and Bow and Barking Railway Junc- tion ; Outfall Sewer, Bridge over Bow and Barking Railway (3 plates) ; Outfall Sewer. Bridge over East London Waterworks' Feeder (2 plates) ; Outfall Sewer, Reservoir (2 plates) ; Steamboat Pier, Waterloo Bridge (3 plates) ; Junction of Sewers, Plans and Sections; Gullies, Plans and Sections; Rolling Stock; Granite and Iron Forts. Outfall Sewer, Tumbling Bay and Outlet ; Out- fall Sewer, Penstocks. South Sidt. Outfall Sewer, Bermondsey Branch (2 plates) ; Outfall " The drawings have a constantly increasing value, and whoever desires to possess clear repre- sentations of the two great works carried out by our Metropolitan Board will obtain Mr. Humber's Yolume." Engineer. HUMBER'S RECORD OF MODERN ENGINEERING. FOURTH SERIES. Imp. 4to, with 36 Double Plates, Photographic Portrait of John Fowler, late Pres. Inst. C.E., and copious descriptive Letterpress, Speci- fications, &c., 3 35. half-morocco. List of the Plates and Diagrams. Abbey Mills Pumping Station, Main Drain- age, Metropolis (4 plates) ; Barrow Docks (5 plates) ; Manquis Viaduct, Santiago and Val- paraiso Railway (2 plates) ; Adam's Locomo- tive, St. Helen's Canal_ Railway (2 plates) ; -harmj; *~ Mesopotamia ; Viaduct over the River Wye, Midland Railway (3 plates) ; St. Germans Via- duct, Cornwall Railway (2 plates) ; Wrought- l ; Millwall Docks Iron Cylinder for Diving (6 plates) ; Milroy's Patent Excavator; Metro- politan District Railway (6 plates); Harbours, Ports, and Breakwaters (3 plates). Cannon Street Station Roof, Charing Cross Railway (3 plates) ; Road Bridge over the River Moka (2 plates); Telegraphic Apparatus for "We gladly welcome another year's issue of this valuable publication from the able pen of Mr. Hu nber. The accuracy and general excellence of this work are well known, while its useful- n-'s-i in giving the mezsurements and details of seme of the latest exa nples of engineer!! g, a; carried out b.y the most eminent men in the profession; cannot be too hjg ily prized."- Artist n, CIVIL ENGINEERING, SURVEYING, etc. MR. HUMBER'S ENGINEERING BOOKS continued. Strains, Calculation of. A HANDY BOOK FOR THE CALCULATION OF STRAINS IN GIRDERS ANDSIMILARSTRUCTURES,AND THEIR STRENGTH. Consisting of Formulae and Corresponding Diagrams, with numerous details for Practical Application, &c. By WILLIAM HUMBER, A-M.Inst.C.E., &c. Fourth Edition. Crown 8vo, nearly 100 Woodcuts and 3 Plates, 75. 6d. cloth. " The formulae are neatly expressed, and the diagrams gcod." Athenaum. " We heartily commend this really handy book to our engineer and architect readers." Eng- lish Mechanic. Barlow's Strength of Materials, enlarged byHumber A TREATISE ON THE STRENGTH OF MATERIALS; with Rules for Application in Architecture, the Construction of Suspension Bridges, Railways, &c. By PETER BARLOW, F.R.S. A New Edition, revised by his Sons, P. W. BARLOW, F.R.S., and W. H. BARLOW, F.R.S. ; to which are added, Experiments by HOOGKINSON, FAIRBAIRN, and KIRKALDY ; and Formulas for Calculating Girders, &c. Arranged and Edited by W. HUMBER, A-M.Inst.C.E. Demy 8vo, 400 pp., with 19 large Plates and numerous Wood- cuts, i8s. cloth. " Valuable alike to the student, tyro, and the experienced practitioner, It will always rank in future, as it has hitherto done, as the standard treatise on that particular subject." Engineer. " There is no greater authority than Barlow." Building News. " As a scientific work of the first class, it deserves a foremost place on the bookshelves of every civil engineer and practical mechanic." English Mechanic. Trigonometrical Surveying. AN OUTLINE OF THE METHOD OF CONDUCTING A TRIGONOMETRICAL SURVEY, for the Formation of Geographical and Topographical Maps and Plans, Military Reconnaissance, Levelling, &c., with Useful Problems, Formulae, and Tables. By Lieut-General FROME, R.E. Fourth Edition, Revised and partly Re- written by Major General Sir CHARLES WARREN, G.C.M.G., R.E. With 19 Plates and 115 Woodcuts, royal 8vo, i6s. cloth. " The simple fact that a fourth edition has been called for Is the best testimony to its merits. No words of praise from us can strengthen the position so well and so steadily maintained by this work. Sir Charles Warren has revised the entire work, and made such additions as were necessary to bring- every portion of the contents up to the present date." Broad Arrow. Field Fortification. A TREATISE ON FIELD FORTIFICATION, THE ATTACK OF FORTRESSES, MILITARY MINING, AND RECONNOITRING. By Colonel I. S. MACAULAY, late Professor of Fortification in the R.M.A., Wool- wich. Sixth Edition, crown 8vo, cloth, with separate Atlas of 12 Plates, izs. Oblique Bridges. A PRACTICAL AND THEORETICAL ESSAY ON OBLIQUE BRIDGES. With 13 large Plates. By the late GEORGE WATSON BUCK, M.I.C.E. Third Edition, revised by his Son, J. H. WATSON BUCK, M.I.C.E. ; and with the addition of Description to Diagrams for Facilitating the Con- struction of Oblique Bridges, by W. H. BARLOW, M.I.C.E. Royal 8vo, izs. cloth. " The standard text-book for all engineers regarding skew arches Is Mr. Buck's treatise, and it would be impossible to consult a better." Engineer. "Mr. Buck's treatise is recognised as a standard text-book, and his treatment has divested the subject of many of the intricacies supposed to belong to it. As a guide to the engineer and archi- tect, on a confessedly difficult subject, Mr. Buck's work is unsurpassed." Building News. Water Storage, Conveyance and Utilisation. \VA TER ENGINEERING : A Practical Treatise on the Measure- ment, Storage, Conveyance and Utilisation of Water for the Supply of Towns, for Mill Power, and for other Purposes. By CHARLES SLAGG, Water and Drainage Engineer, A.M.Inst.C.E., Author of " Sanitary Work in the Smaller Towns, and inVillages," &c. With numerous Illusts. Cr. 8vo. 75. 6d. cloth. " As a small practical treatise on the water supply of towns, and on some applications of water-power, the work is in many respects excellent." Engineering. " The author has collated the results deduced from the experiments of the most eminent authorities, and has presented them in a compact and practical form, accompanied by very clear and detailed explanations. . . . The application of water as a motive power is treated very carefully and exhaustively," Kidldir. "For anyone who desires to begin the study of hydraulics with a consideration of the practical applications of the science there is no better guide." Architect, io CROSBY LOCK WOOD &> SON'S CATALOGUE. Statics, Graphic and Analytic. GRAPHIC AND ANALYTIC STATICS, in their Practical Appli. cation to the Treatment cf Stresses in Roofs, Selid Girders, Lattice, Bowstring and Suspension Bridges, Braced Iron Arches and Piers, and other Frameworks. By R. HUDSON GRAHAM, C.E. Containing Diagrams and Plates to Scale. With numerous Examples, many taken from existing Structures. Specially arranged for Class work in Colleges and Universities. Second Edition, Re- vised and Enlarged. 8vo, i6s. cloth. "Mr. Graham's book will find a place wherever graphic and analytic statics are used or studied." Engineer. " The work is excellent from a practical point of view, and has evidently been prepared with much care. The directions for working- are ample, and are illustrated by an abundance of well- selected examples. It is an excellent text-book for the practical draughtsman." Athtnceum. Student's Text-Booh on Surveying. PRACTICAL SURVEYING: A Text-Book for Students pre- paring for Examination or for Survey-work in the Colonies. By GEORGE VV. USILL, A.M. I. C.E. , Author of "The Statistics of the Water Supply of Great Britain. ".With Four Lithographic Plates and upwards of 330 Illustra- tions. Second Edition, Revised. Crown 8vo, 75. 6d. cloth. [Just published. '' The best forms of instruments are described as to their construction, uses and modes of employment, and there are innumerable hints on work and equipment such as the author, in his experience as surveyor, draughtsman and teacher, has found necessary, and which the student in his inexperience will find most serviceable." Engineer. " The latest treatise in the English language on surveying, and we have no hesitation in say- ing that the student will find it a better guide than any of its predecessors Deserves to be recognised as ths first book which should be put in the hands of a pupil of Civil Bngineering, and every gentleman of education who sets out for the Colonies would find it well to have a copy." Architect. " A very useful, practi densed." Journal of Education. Survey Practice. AID TO SURVEY PRACTICE, for Reference in Surveying, Level- ling, and Setting-out ; and in Route Surveys of Travellers by Land and Sea. With Tables, Illustrations, and Records. By Lowis D'A. JACKSON, A.M.I. C.E., Author of " Hydraulic Manual," "Modern Metrology," &c. Second Edition, Enlarged. Large crown 8vo, 125. 6d. cloth. " Mr. Jackson has produced a valuable vade-mecum for the surveyor. We can recommend this book as containing an admirable supplement to the teaching of the accomplished surveyor." Aihencrunt. " As a text-book we should advise all surveyors to place it in their libraries, and study well the matured instructions afforded in its pages." Colliery Guardian. " The author brings to his work a fortunate union of theory and practical experience which, aided by a clear and lucid style of writing, renders the book a very useful one." Builder. Surveying, Land and Marine. LAND AND MARINE SURVEYING, in Reference to the Pre- paration of Plans for Roads and Railways ; Canals, Rivers, Towns' Water Supplies; Docks and Harbours. With Description and Use of Surveying Instruments. By W. D. HASKOLL, C.E., Author of " Bridge and Viaduct Con- struction," &c. Second Edition, Revised, with Additions. Large cr.Svo, 95. cl. " This book must prove of great value to the student. We have no hesitation in recommend- ing it, feeling assured that it will more than repay a careful study." AT/2ieer. CIVIL ENGINEERING, SURVEYING, etc. n Levelling. A TREATISE ON THE PRINCIPLES AND PRACTICE OF LEVELLING. Showing its Application to purposes of Railway and Civil Engineering, in the Construction of Roads ; with Mr.TELFORD's Rules for the same. By FREDERICK W. SIMMS, F.G.S., M.Inst.C.E. Seventh Edition, with the addition of LAW'S Practical Examples for Setting-out Railway Curves, and TRAUTWINE'S Field Practice of Laying-out Circular Curves. With 7 Plates and numerous Woodcuts, 8vo, 8s. 6d. cloth. *** TRAUTWINE on Curves may be had separate, 55. " The text-book on levelling in most of our engineering schools and colleges." Engineer, " The publishers have rendered a substantial service to the profession, especially to the younger members, by bringing out the present edition of Mr. Simms's useful work." Engineering. Heat, Expansion by. EXPANSION OF STRUCTURES BY HEAT. By JOHN KEILY, C.E., late of the Indian Public Works and Victorian Railway Depart- ments. Crown 8vo, 35. 6d. cloth. SUMMARY OF CONTENTS. Section I. FORMULAS AND DATA. Section II. METAL BARS. Section III. SIMPLE FRAMES. Section IV. COMPLEX FRAMES AND PLATES. Section V. THERMAL CONDUCTIVITY. Section VI. MECHANICAL FORCE OF HEAT. Section VII. WORK OF EXPANSION AND CONTRACTION. Section VIII. SUSPENSION BRIDGES. Section IX. MASONRY. STRUCTURES. " The aim the author has set before him, viz., to show the effects of heat upon metallic and other structures, is a laudable one, for this is a branch of physics upon which the engineer or archi- tect can find but little reliable and comprehensive data in books." Builder. " Whoever is concerned to know the effect of changes of temperature on such structures as suspension bridges and the like, could not do better than consult Mr. Keily's valuable and handy exposition of the geometrical principles involved in these changes." Scotsman. F ractical Mathematics. MATHEMATICS FOR PRACTICAL MEN: Being a Common- place Book of Pure and Mixed Mathematics. Designed chiefly for the use of Civil Engineers, Architects and Surveyors. By OLINTHUS GREGORY, LL.D., F.R.A.S., Enlarged by HENRY LAW, C.E. 4th Edition, carefully Revised by J. R. YOUNG, formerly Professor of Mathematics, Belfast College. With 13 Plates, 8vp, i is. cloth. _" The engineer or architect will here find ready to his hand rules for solving nearly every mathe matical difficulty that may arise in his practice The rules are in all cases explained by means of examples, in which every step of the process is clearly worked out." Builder. On? of the mcst serviceable books for practical mechanics. . . It is an instructive book for the student, and a text-book for him who, having once mastered the subjects it treats of, needs occasionally to refresh his memory upon them." Building News. Hydraulic Tables. HYDRAULIC TABLES, CO-EFFICIENTS, and FORMULA for finding the Discharge of Water from Orifices, Notches, Weirs, Pipes, and Rivers. With New Formulas, Tables, and General Information on Rainfall, Catchment-Basins, Drainage, Sewerage, Water Supply for Towns and Mill Power. By JOHN NEVILLE, Civil Engineer, M.R.I.A. Third Ed., carefully Revised, with considerable Additions. Numerous Illusts. Cr. 8vo, 145. cloth. " Alike valuable to students and engineers in practice ; its study will prevent the annoyance ot avoidable failures, and assist them to select the readiest means of successfully carrying out any given work connected with hydraulic engineering." Mining Journal. " It is, of all English books on the subject, the one nearest to completeness. . . . From the good arrangement of the matter, the clear explanations, and abundance of formulas, the carefully calculated fables, and, above all, the thorough acquaintance with both theory and construction, which is displayed from first to last, the book will be found to be an acquisition." A rchiUct. Hydraulics. HYDRA ULIC MANUAL. Consisting of Working Tables and Explanatory Text. Intended as a Guide in Hydraulic Calculations and Field Operations. By Lowis D'A. JACKSON, Author of "Aid to Survey Practice," " Modern Metrology," &c. Fourth Edition, Enlarged. Large cr. 8vo, i6s. cl. " The author has had a wide experience in hydraulic engineering and has been a careful ob- server of the facts which have come under his notice, and from the great mass of material at his command he has constructed a manual which may be accepted as a trustworthy guide to this branch of the engineer's profession. We can heartily recommend this volume to all who desire to be acquainted with the latest development of this important subject." Engineering. . " The standard-work in this department of mechnnics.' Scotsman. " The most useful feature of this work is its freedom from what is superannuated, and Its thorough adoption of recent experiments ; the text is, in fact, in great part a short account of the great modern experiments. Nature, is CROSBY LOCK WOOD & SON '5 CATALOGUE, Drainage. ON THE DRAINAGE OF LANDS, TOWNS AND BUILD- INGS. By G. D. DEMPSEY, C.E., Author of " The Practical Railway En- gineer," &c. Revised, with large Additions on RECENT PRACTICE IN DRAINAGE ENGINEERING, by D. KINNEAR CLARK, M.Inst.C.E. Author of "Tramways : Their Construction and Working," "A Manual of Rules, Tables, and Data for Mechanical Engineers," &c. &c. Crown 8vo, 75. 6d. cloth. IJitst published. "The new matter added to Mr. Dempsey's excellent work is characterised by the comprehen- sive grasp and accuracy of detail for which the name of Mr. D. K. Clark is a sufficient voucher." Athenaum. " As a work on recent practice in drainage engineering, the book is to be commended to all who are making that branch of engineering science their special study." Iron. " A comprehensive manual on drainage engineering, and a useful introduction to the student." Building News. Tramivays and their Working. TRAMWAYS: THEIR CONSTRUCTION AND WORKING. Embracing a Comprehensive History of the System ; with an exhaustive Analysis of the various Modes of Traction, including Horse-Power, Steam, Heated Water, and Compressed Air ; a Description of the Varieties of Rolling Stock; and ample Details of Cost and Working Expenses: the Progress recently made in Tramway Construction, &c. &c. By D. KINNEAR CLARK, M.InstC.E. With over 200 Wood Engravings, and 13 Folding Plates. Two Vols., large crown 8vo, 305. cloth. " All interested in tramways must refer to it, as all railway engineers have turned to the author's work ' Railway Machinery.'" Engineer. " An exhaustive and practical work on tramways, in which the history of this kind of locomo- tion, and a description and cost of the various modes of laying tramways, are to be found." Buildi*,? Ne-ws. " The best form of rails, the best mode of construction, and the best mechanical appliances are so fairly indicated in the work under review, that any engineer about to construct a tramway will be enabled at once to obtain the practical information which will be of most service to him." Athenaum. Oblique Arches. A PRACTICAL TREATISE ON THE CONSTRUCTION OF OBLIQUE ARCHES. By JOHN HART. Third Edition, with Plates. Im- perial ovo, 8s. cloth. Curves, Tables for Setting-out. TABLE SOP TANGENTIAL ANGLES AND MULTIPLES for Setting-out Curves from 5 to zoo Radius. By ALEXANDER BEAZELEY, M.Inst.C.E. Third Edition. Printed on 48 Cards, and sold in a cloth box, waistcoat-pocket size, 35. 6d. " Each table is printed on a small card, which, being placed on the theodolite, leaves the hands free to manipulate the instrument no small advantage as regards the rapidity of work." Engineer. " Very handy ; a man may know that all his day's work must fall on two of these cards, which he puts into his own card-case, and leaves the rest behind." Athenaum. Earthwork. EARTHWORK TABLES. Showing the Contents in Cubic Yards of Embankments, Cuttings, &c., of Heights or Depths up to an average of 80 feet. By JOSEPH BROADBENT, C.E., and FRANCIS CAMPIN, C.E. Crown 8vo, 55. cloth. "The way in which accuracy is attained, by n simple division ot each cross section into three elements, two in which are constant and one variable, is ingenious." Athen SON'S CATALOGUE. ARCHITECTURE, BUILDING, etc. Construction. THE SCIENCE OF BUILDING : An Elementary Treatise on the Principles of Construction. By E. WYKDHAM TARN, M.A., Architect. Third Edition, Revised and Enlarged, with 59 Engravings. Fcap. 8vo, 45. cloth. [Jus* published. "A very valuable book, which we strongly recommend to all students." Builder. " No architectural student should be without this handbook of constructional knowledge." Architect. Villa Architecture. A HANDY BOOK OF VILLA ARCHITECTURE: Being a Series of Designs for Villa Residences in various Styles. With Outline Specifications and Estimates. By C. WICKES, Architect, Author of "The Spires and Towers of England," &c. 61 Plates, 4to, i us. 6d. half-morocco, gilt edges. " The whole of the designs bear evidence of their being the work of an artistic architect, and they will prove very valuable and suggestive." Building News. Text-Book for Architects. THE ARCHITECT'S GUIDE: Being a Text-Booh of Useful Information for Architects, Engineers, Surveyors, Contractors, Clerks Oj Works, &c. &c. By FREDERICK ROGERS, Architect, Author of " Specifica- tions for Practical Architecture," &c. Second Edition, Revised and Enlarged. With numerous Illustrations. Crown 8vo, 6s. cloth. " As a text-book of useful information for architects, engineers, surveyors, .&c., It would be hard to find a handier or more complete little volume." Standard. "A young architect could hardly have a better guide-book." Timber Trades Journal, Taylor and Cresy's Rome. THE ARCHITECTURAL ANTIQUITIES OF ROME. By the late G. L. TAYLOR, Esq., F.R.I. B.A., and EDWARD CRESY, Esq. New Edition, thoroughly Revised by the Rev. ALEXANDER TAYLOR, M.A. (son of the late G. L. Taylor, Esq.), Fellow of Queen's College, Oxford, and Chap- lain of Gray's Inn. Large folio, with 130 Plates, half-bound, 3 35. N.B. This is the only book which gives on a large scale, and with the precision cf architectural measurement, the principal Monuments of Ancient Rome in plan, elevation, and detail. " Taylor and Cresy's work has from its first publication been ranked among those professional books which cannot be bettered. ... It would be difficult to find eyam >les of drawings, even among those of the most painstaking students of Gothic, more thoroughly worked out than are the one hundred and thirty plates in this volume." Architect. Architectural Drawing. PRACTICAL RULES ON DRA WING, for the Operative Builder and Young Student in Architecture. By GEORGE PYNE. With 14 Plates, 4to, 75. 6d. boards. Sir Wm. Chambers's Treatise on Civil Architecture. THE DECORATIVE PART OF CIVIL ARCHITECTURE. By Sir WILLIAM CHAMBERS, F.R.S. With Portrait, Illustrations, Notes, and an Examination of Grecian Architecture, by JOSEPH GWILT, F.S.A. Revised and Edited by W. H. LEEDS, with a Memoir of the Author. 66 Plates, 4to, 2is. cloth. House Building and Repairing. THE HOUSE-OWNER'S ESTIMATOR ; or, What will it Cost to Build, Alter, or Repair? A Price Book adapted to the Use of Unpro- fessional People, as well as for the Architectural Surveyor and Builder. By JAMES D. SIMON, A.R.I. B.A. Edited and Revised by FRANCIS T. W. MILLER, A.R.I.B.A. With numerous Illustrations. Fourth Edition, Revised. Crown 8vo, as. 6d. cloth. "In two years it will repay its cost a hundred times over." Field, " A very handy book." English Mechanic. Cottages and Villas. COUNTRY AND SUBURBAN COTTAGES AND VILLAS: How to Plan and Build Them. Containing 33 Plates, with Introduction, General Explanations, and Description of each Plate. By JAMES W. BOGUE, Architect, Author of " Domestic Architecture," &c. 4to, xos. 6d. cloth. [Just published. ARCHITECTURE, BUILDING, etc. The New Builder's Price BooJe, 1891. LOCKWOOD'S BUILDER'S PRICE BOOK FOR 1891. A Comprehensive Handbook of the Latest Prices and Data for Builders, Architects, Engineers and Contractors. Re-constructed, Re-written and Greatly Enlarged. By FRANCIS T. W. MILLER. 640 closely-printed pages, crown 8vo, 45, cloth. ' [Just published. " This book is a very useful one, and should find a place in every English office connected with the building and engineering- professions." Industries. "This Price Book has been set up in new type. . . . Advantage has been taken of tho transformation to add much additional information, and the volume is now an excellent book of reference. " Architect. " In its new and revised form this Price Book is what a work of this kind should be compre hensive, reliable, well arranged, legible and well bound.' British Architect. " A work of established reputation." Athenceum. " This very useful handbook is well written, exceedingly clear in its explanations and great care has evidently been taken to ensure accuracy." Mot ning Advertiser Designing, Measuring, and Valuing. THE STUDENTS GUIDE to the PRACTICE of MEASUR- ING AND VALUING ARTIFICERS' WORKS. Containing Directions for taking Dimensions, Abstracting the same, and bringing the Quantities into Bill, with Tables of Constants for Valuation of Labour, and for the Calcula- tion of Areas and Solidities, Originally edited by EDWARD DOBSON, Architect. With Additions on Mensuration and Construction, and a New Chapter on Dilapidations, Repairs, and Contracts, by E. WYNDHAM TARN, M.A. Sixth Edition, including a Complete Form of a Bill of Quantities. With 8 Plates and 63 Woodcuts. Crown 8vo, 75. 6d. cloth. " Well fulfils the promise of its title-page, and we can thoroughly recommend it to the class for whose use it has been compiled. Mr. Tarn's additions and revisions have much increased the usefulness of the work, and have especially augmented its value to students." Engineering. "This edition will be found the most complete treatise on the principles of measuring and valuing artificers' work that has yet been published." Building News. docket Estimator and Technical Guide. THE POCKET TECHNICAL GUIDE, MEASURER AND ESTIMATOR FOR BUILDERS AND SURVEYORS. Containing Tech- nical Directions for Measuring Work in all the Building Trades, Complete Specifications for Houses, Roads, and Drains, and an easy Method of Estimat- ing the parts of a Building collectively. By A. C. BEATON, Author of " Quantities and Measurements," &c. Fifth Edition. With 53 Woodcuts, waistcoat-pocket size, is. 6d. gilt edges. " No builder, architect, surveyor, or valuer should be without his ' Beaton." Building News. "Contains an extraordinary amount of information in daily requisition in measuring and estimating. Its presence in the pocket will save valuable time and trouble." Building World. Donaldson on Specifications. THE HANDBOOK OF SPECIFICATIONS; or, Practical Guide to the Architect, Engineer, Surveyor, and Builder, in drawing up Specifications and Contracts for Works and Constructions. _ Illustrated by Precedents of Buildings actually executed by eminent Architects and En- gineers. By Professor T. L. DONALDSON, P.R.I.B.A., &c. New Edition, in One large Vol., 8vo, with upwards of 1,000 pages of Text, and 33 Plates, i ns.6d. cloth. "In this work forty-four specifications of executed works are given, Including the specifica- tions for parts of the new Houses of Parliament, by Sir Charles Barry, and for the new Royal Exchange, by Mr. Tite, M.P. The latter, in particular, is a very complete and remarkable document. It embodies, to a great extent, as Mr. Donaldson mentions, 'the bill of quantities with tfie description of the works.' ... It is valuable as a record, and more valuable still as a book of precedents. . . . Suffice it to say that Donaldson's ' Handbook of Specifications ' must be bought by all architects." Builder. Bartholomew and Rogers 9 Specifications. SPECIFICATIONS FOR PRACTICAL ARCHITECTURE. A Guide to the Architect, Engineer, Surveyor, and Builder. With an Essay on the Structure and Science of Modern Buildings. Upon the Basis of the Work by ALFRED BARTHOLOMEW, thoroughly Revised, Corrected, and greatly added to by FREDERICK ROGERS, Architect. Second Edition, Revised, with Additions. With numerous Illustrations, medium 8vo, 155. cloth. The collection of specifications prepared by Mr. Rogers on the basis of Bartholomew's work Is too well known to need any recommendation from us. It is one of the books with which every young architect must be equipped ; for time has shown that the specifications cannot be set aside i6 CROSBY LOCK WOOD & SOU >S CATALOGUE. Building ; Civil and Ecclesiastical. A BOOK ON BUILDING, Civil and Ecclesiastical, including Church Restoration ; with the Theory of Domes and the Great Pyramid, &c. By Sir EDMUND BECKETT, Bart., LL.D., F.R. A. S., Author of "Clocks and Watches, and Bells," &c. Second Edition, Enlarged. Fcap. 8vo, 55. cloth. " A book which is always amusing and nearly always instructive. The style throughout is in the highest degree condensed and epigrammatic." Times. Ventilation of Buildings. VENTILATION. A Text Book to the Practice of the Art of Ventilating Buildings. With a Chapter upon Air Testing. By W. P. BUCHAN, R.P., Sanitary and Ventilating Engineer, Author of " Plumbing," &c. With 170 Illustrations. i2mo, 45. cloth boards. [Just published. The Art of Plumbing. PLUMBING. A Text Book to the Practice of the Art or Craft of the Plumber, with Supplementary Chapters on House Drainage, embodying the latest Improvements. By WILLIAM RATON BUCHAN, R.P., Sanitary Engineer and Practical Plumber. Fifth Edition, Enlarged to 370 pages, and 380 Illustrations, izmo, 45. cloth boards. " A text book which may be safely put in the hands of every young plumber, and which will also be found useful by architects and medical professors." Builder. " A valuable text book, and the only treatise which can be regarded as a really reliable manua of the plumber's art." Building News. Geometry for the Architect, Engineer, etc. PRACTICAL GEOMETRY, for the Architect, Engineer and Mechanic. Giving Rules for the Delineation and Application of various Geometrical Lines, Figures and Curves. By E. W. TARN, M.A., Architect, Author of "The Science of Building," &c. Second Edition. With 172 Illus- trations, demy 8vo, 95. cloth. ' No book with the same objects in view has ever been published In which the clearness of the rules laid down and the illustrative diagrams have been so satisfactory." Scotsman. The Science of Geometry. THE GEOMETRY OF COMPASSES; or, Problems Resolved by the mere Description of Circles, and the use of Coloured Diagrams and Symbols. By OLIVER BYRNE. Coloured Plates. Crown 8vo, 35. 6d. cloth. " The treatise is a good one, and remarkable like all Mr. Byrne's contributions to the science of geometry for the lucid character of its teaching." Building News. DECORATIVE ARTS, etc. Woods and Marbles (Imitation of). SCHOOL OF PAINTING FOR THE IMITATION OF WOODS AND MARBLES, as Taught and Practised by A. R. VAN DER BURG and P. VAN DER BURG, Directors of the Rotterdam Painting Institution. Royal folio, iSi by i2Jr in., Illustrated with 24 full-size Coloured Plates; also 12 plain Plates, comprising 154 Figures. Second and Cheaper Edition. Price i ns.6d. List of Plates. i. Various Tools required for Wood Painting a, 3. Walnut: Preliminary Stages of Graining and Finished Specimen 4. Tools used for Marble Painting and Method of Manipulation 5.6. St. Remi Marble: Earlier Operations and Finished Specimen 7. Methods of Sketching different Grains, Knots, Ac. 8. 9. Ash: Pre- liminary Stages and Finished Specimen 10. Methods of Sketching Marble Grains n, la. Breche Marble : Preliminary Stages of Working and Finished Specimen 13. Maple: Methods of Producing the different Grains 14, 15. Bird's- eye Maple: Preliminary Stages and Finished Specimen 16. Methods of Sketching the dif- " White ogany : Specimens s of Manipulation Finished Specimen 19. Mah of various Grains and Method 20, 2i. Mahogany: Earlier Stages and Finished Specimen 22, 23, 24. Sienna Marble : Varieties of Grain, Preliminary Stages and Finished Specimen 25, 26, 27. Juniper Wood : Methods of producing Grain, &c.: Preliminary Stages and Finished Specimen 28, 29, 30. Vert de Mer Marble : Varieties of Grain and Methods of Working Unfinished and Finished Speci- mens 31. 32. 33. Oak: Varieiies of Grain, Tools Employed, and Methods of Manipulation, Pre- liminary Stages and Finished Specimen 34, 35, - Waulsort Marble: Varieties of Grain, Un- " and Finished Specimens. ferent Species of White Marble 17, 18. Marble: Preliminary Stages of Process and *** OPINIONS OF THE PRESS. "Those who desire to attain skill in the art of painting woods and marbles will find advantage In consulting this book. . . . Some of the Working Men's Clubs should give their young men the opportunity to study it." Ruilder. " A comprehensive guide to the art. The explanations of the processes, the manipulation and management of the colours, and the beautifully executed plates will not be the least valuable to U.e Student who aims at making his work a faithful transcript of nature." Eiiilding A'ews. DECORATIVE ARTS, etc. 17 House Decoration. ELEMENTARY DECORATION. A Guide to the Simpler Forms of Everyday Art, as applied to the Interior and Exterior Decoration of Dwelling Houses, &c. By JAMES W. FACEY, Jun. With 68 Cuts, izmo, is. cloth limp. PRACTICAL HOUSE DECORATION : A Guide to the Art of Ornamental Painting, the Arrangement of Colours in Apartments, and the principles of Decorative Design. With some Remarks upon the Nature and Properties of Pigments. By JAMES WILLIAM FACEY, Author of " Elementary Decoration," &c. With numerous Illustrations. i2mo, 25. 6d. cloth limp. N.B.The above Two Works together in One Vol., strongly half-bound, 55. Colour. A GRAMMAR OF COLOURING. Applied to Decorative Painting and the Arts. By GEORGE FIELD. New Edition, Revised, Enlarged, and adapted to the use of the Ornamental Painter and Designer. By ELLIS A. DAVIDSON. With New Coloured Diagrams and Engravings, izmo, 35. 6d. cloth boards. "The book is a most usefu \resume of the properties of pigments." Buildtr. House Painting, Graining, etc. HOUSE PAINTING, GRAINING, MARBLING, AND SIGN WRITING, A Practical Manual of. By ELLIS A. DAVIDSON. Fifth Edition. With Coloured Plates and Wood Engravings, izmo, 6s. cloth boards. " A mass of information, of use to the amateur and of value to the practical man." English Mechanic. "Simply invaluable to the youngster entering upon this particular calling, and highly service- able to the man who is practising it." Furniture Gazette. Decorators, Receipts for. THE DECORATOR'S ASSISTANT: A Modern Guide to De- corative Artists and Amateurs, Painters, Writers, Gilders, &c. Containing upwards of 600 Receipts, Rules and Instructions ; with a variety of Informa- tion for General Work connected with every Class of Interior and Exterior Decorations, &c. Fourth Edition, Revised. 152 pp., crown 8vo, is. in wrapper. " Full of receipts of value to decorators, painters, gilders, &c. The book contains the gist of larger treatises on colour and technical processes. It would be difficult to meet with a work so full of varied information on the painter's art." Building News. " We recommend the work to all who, whether for pleasure or profit, require a guide to decora- tion." Plumber and Decorator. Moyr Smith on Interior Decoration. ORNAMENTAL INTERIORS, ANCIENT AND MODERN. By J. MOYR SMITH. Super-royal 8vo, with 32 full-page Plates and numerous smaller Illustrations, handsomely bound in cloth, gilt top, price i8s. " The book is well illustrated and handsomely got up, and contains some true criticism and a good many yoorial measurement." English Mechanic. Forestry. THE ELEMENTS OF FORESTRY. Designed to afford In- formation concerning the Planting and Care of Forest Trees for Ornament or Profit, with Suggestions upon the Creation and Care of Woodlands. By F. B. HOUGH. Large crown 8vo, IDS. cloth. Timber Importer's Guide. THE TIMBER IMPORTER'S, TIMBER MERCHANT'S AND BUILDER'S STANDARD GUIDE. By RICHARD E. GRANDY. Compris- ing an Analysis of Deal Standards, Home and Foreign, with Comparative Values and Tabular Arrangements for fixing Nett Landed Cost on Baltic and North American Deals, including all intermediate Expenses, Freight, Insurance, &c. &c. Together with copious Information for the Retailer and Builder. Third Edition, Revised, izmo, as. cloth limp. " Everything it pretends to be : built up gradually, it leads one from a forest to a treenail, and throws in, as a raalteweikb^ a host of material concerning bricks, columns, cisterns, &c."nf/is/i Mechanic. MARINE ENGINEERING, NAVIGATION, etc. 2t MARINE ENGINEERING, NAVIGATION, etc. Chain Cables. CHAIN CABLES AND CHAINS. Comprising Sizes and Curves of Links, Studs, &c., Iron for Cables and Chains, Chain Cable and Chain Making, Forming and Welding Links, Strength of Cables and Chains, Certificates for Cables, Marking Cables, Prices of Chain Cables and Chains, Historical Notes, Acts of Parliament, Statutory Tests, Charges for Testing, List of Manufacturers of Cables, &c. &c. By THOMAS W. TRAILL, F.E.R.N., M. Inst. C.E., Engineer Surveyor in Chief, Board of Trade, Inspector of Chain Cable and Anchor Proving Establishments, and General Superin- tendent, Lloyd's Committee on Proving Establishments. With numerous Tables, Illustrations and Lithographic Drawings. Folio, 2 zs. cloth, bevelled boards. "It contains'a vast amount of valuable information. Nothing seems to be wanting to make it a complete and standard work of reference on the subject." Nautical Magazine. Marine Engineering. MARINE ENGINES AND STEAM VESSELS (A Treatise on). By ROBERT MURRAY, C.E. Eighth Edition, thoroughly Revised, with considerable Additions by the Author and by GEORGE CARLISLE, C.E., Senior Surveyor to the Board of Trade at Liverpool. i2mo, 55, cloth boards. " Well adapted to give the young- steamship engineer or marine engine and boil* r maker a general introduction into his practical work." Mechanical World. " We feel sure that this thoroughly revised edition will continue to be as popular in the future as it has been in the past, as, for its size, it contains more useful information than any similar 1 t eatise. ' ' Industries. " As a compendious and useful guide to engineers of our mercantile and royal naval services we should say it cannot be surpassed." Building News. The information given is both sound and sensible, and well qualified to direct young sea- going hands on the straight road to the extra chiet's certificate. Most useful to survej ors, inspectors, draughtsmen, and all young engineers who take an interest in their profession." Glasgow Herald. "An indispensable manual for the student of marine engineering." Liverpool Mercury. Pocket- Booh for Naval Architects and Shipbuilders. THE NAVAL ARCHITECT'S AND SHIPBUILDER'S POCKET-BOOK oj "Formula, Rules, and Tables, and MA RINE ENGINEER'S AND SURVEYOR'S Handy Book of Reference. By CLEMENT MACKROW, Member of the Institution of Naval Architects, Naval Draughtsman. Fourth Edition, Revised. With numerous Diagrams, &c. Fcap., 12$. 6d. strongly bound in leather. "Should be used by all who are engaged in the construction or design of vessels. . . . Will be found to contain the most useful tables and formula: required by shipbuilders, carefully collected from the best authorities, and put together in a popular and simple form." Engineer. "The professional shipbuilder has now, in a convenient and accessible form, reliable data for solving many of the numerous problems that present themselves in the course of his work." Iron. "There is scarcely a subject on which a naval architect or shipbuilder can require to refresh his memory which will not be found within the covers of Mr. Mackrow'sbook." English. Mechanic. Docket-Book for Marine Engineers. A POCKET-BOOK OF USEFUL TABLES AND FOF- MULM FOR MARINE ENGINEERS. By FRANK PROCTOR, A.I.N.A, Third Edition. Royal 32010, leather, gilt edges, with strap, 45. " We recommend it to our readers as going far to supply a long-felt want." Naval Science. "A most useful companion to all marine engineers." United Service Gaxette. Introduction to Marine Engineer ing. ELEMENTARY ENGINEERING : A Manual for Young Marine Engineers and Apprentices. In the Form of Questions and Answers on Metals, Alloys, Strength of Materials, Construction and Management of Marine Engines and Boilers, Geometry, &c. &c. With an Appendix of Useful Tables. By JOHN SHERREN BREWER, Government Marine Surveyor, Hong- kong. Small crown 8vo, 2s. cloth. " Contains much valuable information for the class for whom it is intended, especially in the chapters on the management of boilers and eng nes." Nautical Magazine. " A useful introduction to the more elaborate text books." Scotsman. " To a student who nas the requisite desire and resolve to attain a thorough knowledge, Mr. Brewer otfers decidedly useful help."' Athenaum. Navigation. PRACTICAL NAVIGATION. Consisting of THE SAILOR'S SEA-BOOK, by JAMES GREENWOOD and W. H. ROSSES; together with the requisite Mathematical and Nautical Tables for the Wo:king of the P oblpms, by HENRY LAW, C.E., and Professor J. R. YOUNG. Illustrated, izmo, ;s. strongly hali-bounc 1 . 22 CROSBY LOCKWOOD & SON'S CATALOGUE. MINING AND METALLURGY. Metalliferous Mining in the United Kingdom. BRITISH MINING : A Treatise on the History, Discovery, Practical Development, and Future Prospects of Metalliferous Mines in the United King- dom. By ROBERT HUNT, F.R.S., Keeper of Mining Records ; Editor of " Ure's Dictionary of Arts, Manufactures, and Mines," &c. Upwards of 950 pp., with 230 Illustrations. Second Edition, Revised. Super-royal 8vo, 2 2S. cloth. "One of the most valuable works of reference of modern times. Mr. Hunt, as keeper of mining records of the United Kingdom, has had opportunities for such a task not enjoyed by anyone else, and has evidently made the most of them. . . . The language and style adopted are good, and the treatment of the various subjects laborious, conscientious, and scientific." Engineering; "The book is, in fact, a treasure-house of statistical information on mininer subjects, and we know of no other work embodying so great a mass of matter of this kind. Were this the only merit ef Mr. Hunt s volume, it would be sufficient to render it indispensable in this library of everyone interested in the development of the mining and metallurgical industries of this country." Athenaum. _ "A mass of information not elsewhere available, and of the greatest value to those who may be interested in our great minoral industries." Engineer. " A sound, business-like collection of interesting facts. . . . The amount of information Mr. Hunt has brought together is enormous. . . . The volume appears likely to convey more instruction upon the subject than any work hitherto published." Mining- yournal. Colliery Management. THE COLLIERY MANAGER'S HANDBOOK; A Compre- hensive Treatise on the Laying-out and Working of Collieries, Designed as a Book of Reference for Colliery Managers, and for the Use of Coal-Mining Students preparing for First-class Certificates. By CALEB PAMELY, Mining Engineer and Surveyor; Member of the North of England Institute of Mining and Mechanical Engineers; and Member of the South Wales Insii- tute of Mining Engineers. With nearly 500 Plans, Diagrams, and other Illustrations. Medium 8vo, about Coo pages. Price i 55. strongly bound. [.Just ready. Coal and Iron. THE COAL AND IRON INDUSTRIES OF THE UNITED KINGDOM. Comprising a Description of the Coal Fields, and of the Principal Seams of Coal, with Returns of their Produce and its Distribu- tion, and Analyses of Special Varieties. Also an Account of the occurrence of Iron Ores in Veins or Seams ; Analyses oi each Variety ; and a History ot the Rise and Progress of Pig Iron Manufacture. By RICHARD MEADE, Assistant Keeper of Mining Records. With Maps. 8vo, i 8s. cloth. " The book is one which must find a place on the shelves of all Interested In coal and iron production, and in the iron, steel, and other metallurgical industries." Engineer. " Of this book we may unreservedly say that it is the best of its class which we have ever met. ... A book of reference which no one engaged in the iron or coal trades should omit from his library." Iron and Coal Trades Review. frospecting for Gold and other Metals. THE PROSPECTOR'S HANDBOOK: A Guide for the Pro- spector and Traveller in Search of Metal-Bearing or other Valuable Minerals. By J. W. ANDERSON, M.A. (Camb.), F.R.G.S., Author of "Fiji and New Caledonia." Fifth. Edition, thoroughly Revised and Enlarged. Small crown 8vo, 35. 6d. cloth. "Will supply a much felt want, espec ; ally among Colonists, in whose way are so often thrown many mineralogical specimens the value of which it is difficult to determine." F.ngineer. "How to find commercial minerals, and how to identify them when they are found, are the leading points to which attention is directed. The au;hor has managed to pack as much practical detail into his pages as would supply material for a book three times its size." Mining- Journal. Mining Notes and Formula?. NOTES AND FORMULAE FOR MINING STUDENTS. By JOHN HERMAN MERIVALE, M.A., Certificated Colliery Manager, Professor of Mining in the Durham College of Science, Newcastle-upon-Tyne. Third Edition, Revised and Enlarged. Small crown 8vo, zs. 6d. cloth. [Just published. " Invaluable to anyone who is working up for an examination on mining subjects." Coal and Iron Trades Review. " The author has done his work in an exceedingly creditable manner, and has produced a book that will be of service to students, and those who are practically engaged in mining operations. 1 ' Engineer. " A vast amount of technical matter of the utmost value to mining engineers, and of consider- able interest to students." Schoolmaster, MINING AND METALLURGY. 23 Explosives. A HANDBOOK ON MODERN EXPLOSIVES. Being a Practical Treatise on the Manufacture and Application of Dynamite, Gun- Cotton, Nitro-Glycerine and other Explosive Compounds. Including the Manufacture of Collodion-Cotton. By M. EISSLER, Mining Engineer and Metallurgical Chemist, Author of "The Metallurgy _ of Gold," "The Metallurgy of Silver," &c. With about 100 Illustrations. Crown 8vo, LOS. 6d. cloth. [Just published. "Useful not only to the miner, but also to officers of both services to whom blasting and the use of explosives generally may at any time become a necessary auxiliary." Nature. " A veritable mine of information on the subject of explosives employed for military, mining and blasting purposes." Army and Navy Gazette. " The book is clearly written. Taken as a whole, we consider it an excellent little book and one that should be found of great service to miners and others who are engaged in work requiring the use of explosives." Atheneeum, Gold) Metallurgy of. THE METALLURGY OF GOLD : A Practical Treatise on the Metallurgical Treatment of Gold-bearing Ores. Including the Processes of Concentration and Cnlorination, and the Assaying, Melting and Refining of Gold. By M. EISSLER, Mining Engineer and Metallurgical Chemist, formerly Assistant Assayer of the U. S. Mint, San Francisco. Third Edition, Revised and greatly Enlarged. With 187 Illustrations. Crown 8vo, I2s. 6d. cloth. [Just published. " This book thoroughly deserves its title of a ' Practical Treatise.' The whole process of gold milling, from the breaking of the quartz to the assay of the bullion, is described in clear and orderly narrative and with much, but not too much, fulness of detail." Saturday Review. " The work is a storehouse of information and valuable data, and we strongly recommend it to all professional men engaged in the gold-mining industry." Mining yournal. Silver, Metallurgy of. THE METALLURGY OF SILVER : A Practical Treatise on the Amalgamation, Roasting and Lixiviation of Silver Ores. Including the Assaying, Melting and Refining of Silver Bullion. By M. EISSLER, Author of "The Metallurgy of Gold ."' With 124 Illustrations. Crown 8vo, IDS. 6d " A practical treatise, and a technical work which we are convinced will supply a long-felt want amongst practical men, and at the same time be of value to students and others indirectly connected with the industries." Mining Journal. " From first to last the book is thoroughly sound and reliable. Colliery Guardian, " Kor chemists, practical miners, assayers and investors alike, we do not know of any work on the subject so handy and yet so comprehensive." Glasgow Herald. Silver-Lead, Metallurgy of. THE METALLURGY OF ARGENTIFEROUS LEAD ORES A Practical Treatise on the Smelting of Silver-Lead Ores and the Refining of Lead Bullion. Illustrated with Plans and Sections of Smelting Furnaces and Plant in Europe and America. By M. EISSLER, Author of "The Me- tallurgy of Gold," " The Metallurgy of Silver," &c. Cr. 8vo. [In the press. Metalliferous Minerals and Mining. TREATISE ON METALLIFEROUS MINERALS AND MINING. By D. C. DAVIES, F.G.S., Mining Engineer, &c., Author of "A Treatise on Slate and Slate Quarrying." Illustrated with numerous Wood Engravings. Fourth Edition, carefully Revised. Crown 8vo, 125. 6d. cloth. "Neither the practical miner nor the general reader interested in mines can have a better book or his companion and his guide." Mining- Journal. " We are doing our readers a service in calling their attention to this valuable work ' Mining- World. " A book that will not only be useful to the geologist, the practical miner, and the metallurgist, but also very interesting to the general public." Iron. "As a history of the present state of mining throughout the world this book has a real value, and it supplies an actual vzxAS'Athenczum. Earthy Minerals and Mining. A TREATISE ON EARTHY & OTHER MINERALS AND MINING. By D. C. DAVIES, F.G.S. Uniform with, and forming a Com- panion Volume to, the same Author's " Metalliferous Minerals and Mining." With 76 Wood Engravings. Second Edition. Crown 8vo, I2S. 6d. cloth. " We do not remember to have met with any English work on mining matters that contains the same amount of information packed in equally convenient form." Academy. " We should be inclined to rank it as among the very best of the handy technical and trades manuals which have recently appeared." British Quarterly Review, 24 CROSBY LOCK WOOD & SON'S CATALOGUE. Mineral Surveying and Valuing. THE MINERAL SURVEYOR AND VALUER'S COMPLETE G UIDE, comprising a Treatise on Improved Mining Surveying and the Valua* tion of Mining Properties, with New Traverse Tables. By WM. LINTERN, Mining and Civil Engineer. Third Edition, with an Appendix on " Magnetic and Angular Surveying," with Records" of the Peculiarities of Needle Dis- turbances. With Four Plates of Diagrams, Plans, &c. izmo, 45. cloth. [Just published. " Mr. Lintern's book forms a valuable and thoroughly trustworthy guide." Iron and Coal Trades Review. " This new edition must be of the highest value to colliery surveyors, proprietors and mana- gers." Colliery Guardian. Asbestos and its Uses. ASBESTOS: Its Properties, Occurrence and Uses. With some Account of the Mines of Italy and Canada. By ROBERT H.JONES. With Eight Collotype Plates and other Illustrations. Crown 8vo, i2s. 6d. cloth. [Just published. " An interesting and invaluable work." Collierv Guardian. " We counsel our readers to get this exceedingly interesting work for themselves : they will find in it much that is suggestive, and a great deal that is of immediate and practical usefulness." Builder. " A valuable addition to the architect's and engineer's library." Building Nt7t>s. Underground Pumping Machinery. MINE DRAINAGE. Being a Complete and Practical Treatise on Direct-Acting Underground Steam Pumping Machinery, with a Descrip- tion of a large number of the best known Engines, their General Utility and the Special Sphere of their Action, the Mode of their Application, and their merits compared with other forms of Pumping Machinery. By STEPHEN MICHELL. 8vo, 155. cloth. "Will be highly esteemed by colliery owners and lessees, mining engineers, and students generally who require to be acquainted with the best means of securing the drainage of mines. It is a most valuable work, and stands almost alone in the literature of steam pumping machinery." Colliery Guardian. " Much valuable information is given, so that the book is thoroughly worthy of an extensive circulation amongst practical men and purchasers of machinery." Alining- Journal. Mining Tools. A MANUAL OF MINING TOOLS. For the Use of Mine Managers, Agents, Students, &c. By WILLIAM MORGANS, Lecturer on Prac- tical Mining at the Bristol School of Mines. 12010, as. 6d. cloth limp. ATLAS OF ENGRAVINGS to Illustrate the above, contain- ing 235 Illustrations of Mining Tools, drawn to scale. 4to, 45. 6d. cloth. "Students in the science of mining, and overmen, captains, managers, and viewers may gain practical knowledge and useful hints by the study of Mr. Morgans' manual." Colliery Guardian. "A valuable work, which will tend materially to improve our mining literature." Mining Journal. Coal Mining. COAL AND COAL MINING: A Rudimentary Treatise on. By the late Sir WARINGTON W. SMYTH, M.A., F.R.S., &c., Chief Inspector of the Mines of the Crown. Seventh Edition, Revised and Enlarged. With numerous Illustrations, izmo, 45. cloth boards. [.7's* publishfcl. "As an outline is given of every known coal-field in this and other countries, as well as of the principal methods of working, the Book will doubtless interest a very large number of readers." Mining Journal. Subterraneous Surveying. SUBTERRANEOUS SURVEYING, Elementary and Practical Treatise on, with and without the Magnetic Needle. ByTHOMAS FENWICK, Surveyor of Mines, and THOMAS BAKER, C.E. Illust. i2mo, 35. cloth boards. Granite Quarrying. GRANITES AND OUR GRANITE INDUSTRIES. By GEORGE F. HARRIS, F.G.S., Membre de la Societe Beige de Gdologie, Lec- turer on Economic Geology at the Birkbeck Institution, &c. With Illustra- tions. Crown 8vo, zs. 6d. cloth. " A clearly and well-written manual for persons engaged or interested in the granite industry. Scotsman. " An interesting work, which will be deservedly esteemed." Colliery Guardian. " An exceedingly interesting and valuable monograph on a subject which has hitherto received unaccountably little attention in the shape of systematic literary treatment." Scottish Leader. , ELECTRICAL ENGINEERING, tit. ELECTRICITY, ELECTRICAL ENGINEERING, etc. Electrical Engineering. THE ELECTRICAL ENGINEER'S POCKET-BOOK OF MODERN RULES, FORMULAE, TABLES AND DATA. By H. R. KEMPE, M.Inst.E.E., A.M.Inst C.E., Technical Officer Postal Telegraphs, Author of "A Handbook of Electrical Testing," &c. With numerous Illus- trations, royal 32010, oblong, 55. leather. \_Just published. " There is very little in the shape of formulce or data which the electrician is likely to want in a hmry which cannot be found in its pages " Practical Engineer. " A very useful book of re f erence for daily use in practical electrical engineering and its various applications to the industries of the present day." Iron. " It is the best book of its kind." Electrical Engineer. "Wei arranged and compact. The Electrical Engineer's Pocket- Book is a good one." Electrician. ' Strongly recommended to those engaged in the various electric.d industries." Electrical Electric Lighting. ELECTRIC LIGHT FITTING : A Handbook for Working Electrical Engineers, embodying Practical Notes on Installation Manage- ment. By JOHN W. UROUHART, Electrician, Author of " Electric Light," &c. With numerous Illustrations, crown 8vo, 55. cloth. [Just published. " This volume deals with what may be termed the mechanics of electric lighting, and is addressed to mtn who are already engaged in the work or are training for it. The work traverses a great dtal of ground, and may be read as a sequel to the same author's useful wonc on ' Electric Light.' "Electrician. " This is an attempt to state in the simplest language the precautions which should be adopted in instal ing the electric light, and to give information. for the guidance of those who have to run the plant when installed. The book is well wonh the perusal of the workmen for whom it is w.itten." Electrical Review. ' Eminently practical and useful. . . . Ought to be in ths hands of everyone in charge of an electric light plant.' Electrical Engineer. " Altogether Mr. Urquhart has succeeded in producing a rf ally capital book, which we have no hesitanon in recommending to the notice of working electricians ana electrical engineers. MeJiamcal World. Electric Light. ELECTRIC LIGHT : Its Production and Use. Embodying Plain Directions for the Treatment cf Dynamo-Electric Machines, Eateries Accumulators, and Electric Lamps, by J. W. URQUHART, C.E., Author of " Electric Light Fittiner," "Electroplating," &c. Fourth Edition, carefully Revised,with Large Additions and 145 Illustrations. Crown 8vo, 75. 6e of Engineer Constructors and Electricians in Charge. With Examples of leading English, Ameucan and Continental Dynamos and Motors. By J. W. URQUHART, Author of "Electric Light," "Electric Light Fitting," &c. Crown 8vo. \_ln the press. Text Book of Electricity. THE STUDENTS TEXT-BOOK OF ELECTRICITY. By HENRY M. NOAD, Ph.D., F.R.S., F.C.S. New Edition, carefully Revised. With an Introduction and Additional Chapters, by W. H. PREECE, M.I.C.E., Vice- President of the Society of Telegraph Engineers, &c. With 470 Illustra- tions. Crown 8vo, izs. 6d. cloth. "The original plan of this book has been carefully adhered to so as to make it a reflex of the existing state of electrical science, adapted for students. . . . Discovery seems to have pro- gressed with marvellous strides ; nevertheless it has now apparently ceased, and practical applica tions have commenced their career ; and it is to give a faithful account of these that this fresh edition of Dr. Noad's valuable text-book is launched forth." Extractfrom Introduction by W. H. Preece, Esq. "We can recommend Dr. Noad's book for clear style, great range of subject, a good index, and a plethora of woodcuts. Such collections as the present are indispensable." Athenaurn. " An admirable text book for every student beginner or advanced of electricity." Engineering. 26 CROSBY LOCKWOOD &- SON'S CATALOGUE. Electric Light my. THE ELEMENTARY PRINCIPLES OF ELECTRIC LIGHT- ING. By ALAN A. CAMPBELL SWINTON, Associate I.E.E. Second Edition, Enlarged and Revised. With 16 Illustrations. Crown 8vo, is. 6d. cloth. "Anyone who desires a short and thoroughly clear exposition of the elementary principles of electric-lighting cannot do better than read this little work." Bradford Observer. Electricity. A MANUAL OF ELECTRICITY: Including Galvanism, Mag. netism, Dia-Magnetism, Electro-Dynamics, Magno-Electricity, and the Electric Telegraph. By HENRY M. NOAD, Ph.D., F.R.S., F.C.S. Fourth Edition. With 500 Woodcuts. 8vo, i 45. cloth. "It is worthy of a place in the library of every public institution." Mining Journal. Dynamo Construction. HO W TO MAKE A DYNAMO : A Practical Treatise for Amateurs. Containing numerous Illustrations and Detailed Instructions for Construct- ing a Small Dynamo, to Produce the Electric Light. By ALFRED CROFTS. Third Edition, Revised and Enlarged. Crown 8vo,2s. cloth. [Just published. "The instructions given in this unpretentious little book are sufficiently clear and explicit to enable any amateur mechanic possessed of average skill and the usual tools to be found in an amateur's workshop, to build a practical dynamo machine." Electrician. NATURAL SCIENCE, etc. Pneumatics and Acoustics. PNEUMATICS : including Acoustics and the Phenomena, of Wind Currents, for the Use of Beginners. By CHARLES TOMLINSON, F.R.S., F.C.S., &c. Fourth Edition, Enlarged. With numerous Illustrations. i2mo, is. 6d. cloth. " Beginners in thestudy of this important application of science could not have a better manua Scotsman. " A valuable and suitable text-book for students of Acoustics and the Phenomena of Wind Currents." Schoolmaster. Conchology. A MANUAL OF THE MOLLUSC A : Being a Treatise on Recent and Fossil Shells. By S. P. WOODWARD, A.L.S., F.G.S., late Assistant Palaeontologist in the British Museum. With an Appendix on Recent and Fossil Conchological Discoveries, by RALPH TATE, A.L.S., F.G.S. Illustrated by A. N. WATERHOUSE and JOSEPH WILSON LOWRY. With 23 Plates and upwards of 300 Woodcuts. Reprint of Fourth Ed., 1880. Cr. 8vo, 75. 6d. cl. " A most valuable storehouse of Conchological and geological information." Science Gossip. Geology. RUDIMENTARY TREATISE ON GEOLOGY, PHYSICAL AND HISTORICAL. Consisting of "Physical Geology," which sets forth the leading Principles of the Science ; and " Historical Geology," which treats of the Mineral and Organic Conditions of the Earth at each successive epoch, especial reference being made to the British Series of Rocks. By RALPH TATE, A.L.S., F.G.S., &c. &c. With 250 Illustrations, izmo, 51. cloth boards. " The fulness of the matter has elevated the book into a manual. Its information is exhausth e and well arranged." School Board Chronicle. Geology and Genesis. THE TWIN RECORDS OF CREATION; or, Geology and Genesis : their Perfect Harmony and Wonderful Concord. By GEORGE W. VICTOR LE VAUX. Numerous Illustrations. Fcap. 8vo, 55. cloth. " A valuable contribution to the evidences of Revelation, and disposes very conclusively of the arguments of those who would set God's Works against God's Word. No real difficulty is shirked, and no sophistry is left unexposed." The Rock, " The remarkable peculiarity of this author is that he combines an unbounded admiration of science with an unbounded admiration of the Written record. The two impulses are balanced to a nicety ; and the consequence is that difficulties, which to minds less evenly poised would be seri- ous, find immediate solutions of the happiest kinds." London Review. Astronomy. ASTRONOMY. By the late Rev. ROBERT MAIN, M.A. , F.R.S., formerly Radclifie Observer at Oxford. Third Edition, Revised and Cor- rected to the present time, by WILLIAM THYNNE LYNN, B.A., F.R.A.S., formerly of the Royal Observatory, Greenwich. i2mo, 2S. cloth limp. "A sound and simple treatise, very carefully edited, and a capital book for beginners." Kn SON'S CATALOGUE. JFlour Manufacture, Milling, etc. FLOUR MANUFACTURE: A Treatise on Milling Science and Practice. By FRIEDRICH KICK, Imperial Regierungsrath, Professor of Mechanical Technology in the Imperial German Polytechnic Institute, Prague. Translated from the Second Enlarged and Revised Edition with Supplement. By H. H. P. POWLES, A.M.I.C.E. Nearly 400 pp. Illustratec with 28 Folding Plates, and 167 Woodcuts. Royal 8vo, 255. cloth. This valuable work is. and will remain, the standard authority on the science of milling. , . The miller v. ho has read and digested this wO'k will have laid the foundation, so to speak, of a suc- cessful career ; he will have acquired a number of general principles which he can proceed to apply. In this handsome volume we at last have the accepted text-book of modern millmgingood, sound English, which has little, if any, trace of the German idiom." The Miller. " the appearance of this celebrated work in English is very opportune, and British millers wi'l, we are sure, not be slow in availing themselves of its pages." Millers' Gazette. Small Farming. SYSTEMATIC SMALL FARMING; or, The Lessons of my Farm. Being an Introduction to Modern Farm Practice for Small Farmers in the Culture of Croos; The Feeding of Cattle; The Management of the Dairy, Poultry and Pis;?, &c. &c. By ROBERT SCOTT BURN, Author of " Out- lines of Landed Estates' Management." Numerous Illusts., cr. 8vo, 6s. cloth. "This is the completest book of its class we have seen, and one which every amateur farmer will read with pleasure and accept as a guide." Field. "The volume contains a vast amount of useful information. No branch of farming is let untouched, from the labour to be done to the results achieved. It mny be safely recommended to all who think they will be in paradise when they buy or rent a three-acre farm." Glasgow Herald, J&odern Farming. OUTLINES OF MODERN FARMING. By R. SCOTT BURN. Soils, Manures, and Crops Farming aad Farming Economy Cattle, Sheep, and Horses Management of Dairy, Pigs and Poultry Utilisation of Town-Sewage, Irrigation, &c. Sixth Edition. In One Vol., 1,250 pp., half- bound, profusely Illustrated, 125. " The aim of the author has been to make his work at once comprehensive and trustworthy, and in this aim he has succeeded to a degree which entitles him to much credit." Morning Advertiser. "No farmer should be without this book." Banbury Guardian. Agricultural Engineering. FARM ENGINEERING, THE COMPLETE TEXT-BOOK OF. Comprising Draining and Embanking ; Irrigation and Water Supply ; Farm Roads, Fences, and Gates ; Farm Buildings, their Arrangement and Con- struction, with Plans and Estimates; Barn Implements and Machines; Field Implements and Machines; Agricultural Surveying, Levelling, &c. By Prof. JOHN SCOTT, Editor of the " Farmers' Gazette," late Professor of Agriculture and Rural Economy at the Royal Agricultural College, Cirencester, &c. &c. In One Vol., 1,150 pages, half-bound, with over 6co Illustrations, 125. " Written with great care, as well as with knowledg-e and ability. The author has done his work well ; we have found him a very trustworthy guide wherever we have tested his statements. The volume will be of great value to agricultural students." Mark Lane Express. ' ' For a young agriculturist we know of ,no handy volume likely to be more usefully studied," BelCs Weekly Messenger. English Agriculture. THE FIELDS OF GREAT BRITAIN : A Text-Book of Agriculture, adapted to the Syllabus of the Science and Art Department. For Elementary and Advanced Students. By HUGH CLEMENTS (Board of Trade). Second Ed., Revised, with Additions. i8mo, 2S. 6d. cl. [Just published. "Amost comprehensive volume, giving a mass of information." Agricultural Economist. "It is a long time since we have seen a book which h.is pleased us more, or which contains such a vast and useful fund of knowledge." Educational Times. Tables for Farmers, etc. TABLES, MEMORANDA, AND CALCULATED RESULTS for Farmers, Graziers, Agricultural Students, Surveyors, Land Agents Auc- tioneers, etc. With a New System of Farm Book-keeping. Selected and Arranged by SIDNEY FRANCIS. Second Edition, Revised. 272 pp., waist- coat-pocket size, is. 6d. limp leather. [Just published. " Weighing less than i oz., and occupying no more space than a match box, it contains a mass of facts and calculations which has never before, in such handy form, been obtainable. . Every operation on the farm is dealt with. The work may be taken as thoroughly accurate, the whole of tne tables having been revised by Dr. Fream. We cordially recommend it." Bell's Weekly Messenger. " A marvellous little book. . . . The agriculturist who possesses himself of it will not be disappointed with his investment." The Farm. AGRICULTURE, FARMING, GARDENING, etc. 37 Farm and Estate Boole-keeping. BOOK-KEEPING FOR FARMERS 6- ESTATE OWNERS. A Practical Treatise, presenting, in Three Plans, a System adapted for all Classes of Farms. By JOHNSON M. WOODMAN, Chartered Accountant. Second Edition, Revised. Cr. 8vo, 35. 6d. cl. bds. ; or 2S. 6d. cl. limp. [Just published* " The volume is a capital study of a most important subject." Agricultural Gazette. " Will be found of great assistance by those who intend to commence a system of book-keep- ing 1 , the author's examples being clear and explicit, and his explanations, while full and accurate*, being to a large extent free from technicalities." tz/< Stock Journal. Farm Account Book. WOODMAN'S YEARLY FARM ACCOUNT BOOK. Giving a Weekly Labour Account and Diary, and showing the Income and Expen- diture under each Department of Crops, Live Stock, Dairy, &c. &c. With- Valuation, Profit and Loss Account, and Balance Sheet at the end of the- Year, and an Appendix of Forms. Ruled and Headed for Entering a Com- plete Record of the Farming Operations. By JOHNSON M. WOODMAN,, Chartered Accountant, Author of " Book-keeping for Farmers." Folio, 75. 6d. half bound. [culture. "Contains every requisite form for keeping farm accounts readily and accurately." Agri- Early Fruits, Flotvers and Vegetables. THE FORCING GARDEN ; or, How to Grow Early Fruits* Flowers, and Vegetables. With Plans and Estimates for Building Glass- houses, Pits and Frames. Containing also Original Plansfor Double Glazing, a New Method of Growing the Gooseberry under Glass, &c. &c., and on Venti- lation, Protecting Vine Borders, &c. With Illustrations. By SAMUEL WOOD. Crown 8vo, 35. 6d. cloth. " A good book, and fairly fills a place that was in some decree vacant. The book is written with great care, and contains a great deal of valuable teaching." Gardeners' Magazine. " Mr. Wood's book is an original and exhaustive answer to the question ' How to Grow Earl> Fruits, Flowers and Vegetables J ' "Land and Water. Good Gardening. A PLAIN GUIDE TO GOOD GARDENING ; or, How to Grow Vegetables, Fruits, and Flowers. With Practical Notes on Soils, Manures,. Seeds, Planting, Laying-put of Gardens and Grounds, &c. By S. WOOD. Fourth Edition, with considerable Additions, &c., and numerous Illustrations., Crown 8vo, 35. 6d. cloth. "A very good book, and one to be highly recommended as a practical guide. The practical directions are excellent." Athentzum. " May be recommended to young gardeners, cottagers, and specially to amateurs, for the plain, simple, and trustworthy information it gives on common matters too often neglected." Gardeners' Chronicle. Gainful Gardening. MULTUM-IN-PARVO GARDENING: cr, How to make One Acre of Land produce 620 a-year by the Cultivation of Fruits and Vegetables ; also, How to Grow Flowers in Three Glass Houses, so as to realise 176 per annum clear Profit. By SAMUEL WOOD, Author of " Good Gardening,' 1 &c. Fifth and cheaper Edition, Revised, with Additions. Crown 8vo, is. sewed. "We are bound to recommend it as not only suited to the case of the amateur and gentleman's gardener, but to the market grower." Gardeners' Magazine. Gardening for Ladies. THE LADIES' MULTUM-IN-PARVO FLOWER GARDEN,, and Amateurs' Complete Guide. By S. WOOD. With Illusts. Cr. 8vo, 33. 6d. cl " This volume contains a good deal of sound, common sense instruction." Florist. " Full of shrewd hints and useful instructions, based on a lifetime of experience." Scotsman. Receipts for Gardeners. GARDEN RECEIPTS. Edited by CHARLES W. QUIN. 12010,, is. 6d. cloth limp. "A useful and handy book, containing a good deal of valuable information." Athenaum. Market Gardening. MARKET AND KITCHEN GARDENING. By Contributors to "The Garden." Compiled by C. W. SHAW, late Editor of "Gardening Illustrated." i2mo, 3s. 6d. cloth boards. [Just published. " Tke most valuable compendium of kitchen and market-garden work published." farmer. Cottage Gardening. COTTAGE GARDENING; or, Flowers, Fruits, and Vegetables fop Small Gardens. By E. HOBDAY, ijmo, is. 6d. cloth limp. Contains much useful information at a small charge." Glasgow Herald. 38 CROSBY LOCK WOOD & SON'S CATALOGUE. LAND AND ESTATE MANAGEMENT, LAW, etc. Hudson's Land Valuer's Pocket-Book. THE LAND VALUER'S BEST ASSISTANT: Being Tables on a very much Improved Plan, for Calculating the Value of Estates. With Tables lor reducing Scotch, Irish, and Provincial Customary Acres to Statute Measure, &c. By R. HUDSON, C.E. New Edition. Royal 32010, leather, elastic band, 45. "This new edition includes tables for ascertaining the value of leases for any term of years ; and for showing how to lay put plots of ground of certain acres in forms, square, round, &c., with valuable rules for ascertaining the probable worth of standing timber to any amount ; and is of incalculable value to the country gentleman and professional man." Farmers Journal. Ewart's Land Improver's Pocket-Book. THE LAND IMPROVER'S POCKET-BOOK OF FORMULA, TABLES and MEMORANDA required in any Computation relating to the Permanent Improvement of Landed Property. By JOHN EWART, Land Surveyor and Agricultural Engineer. Second Edition, Revised. Royal 32010, oblong, leather, gilt edges, with elastic band, 45. ' A compendious and handy little volume." Spectator. Complete Agricultural Surveyor's Pocket-Book. THE LAND VALUER'S AND LAND IMPROVER'S COM- PLETE POCKET-BOOK. Consisting of the above Two Works bound to- gether. Leather, gilt edges, with strap, 75. 6d. " Hudson's book is the best ready-reckoner on matters relating to the valuation of land and crops, and its combination with Mr. Ewart's work greatly enhances the value and usefulness of the tatter-mentioned. . . . It is most useful as a manual for reference." North of Engla nd Farmer. Auctioneer's Assistant. THE APPRAISER, A UCTIONEER, BROKER, HOUSE AND ESTA TE A GENT AND VAL UER'S POCKE T A SSISTA NT, tor the Valua- tion for Purchase, Sale, or Renewal of Leases, Annuities and Reversions, and of property generally; with Prices for Inventories, &c. By JOHN WHEELER, Valuer, &c. Fifth Edition, re-written and greatly extended by C. N ORRIS, Surveyor, Valuer, &c. Royal 32010, 55. cloth. " A neat and concise book of reference, containing an admirable and clearly-arranged list ol prices for inventories, and a very practical guide to determine the value of furniture,&c." Standard, " Contains a large quantity of varied and useful information as to the valuation for purchase, sale, or renewal of leases, annuities and reversions, and of property generally, with prices for inventories, and a guide to determine the value of interior fittings and other effects." Builder. Auctioneering. A UCTIONEERS : . Their Duties and Liabilities. A Manual of Instruction and Counsel for the Young Auctioneer. By ROBERT SQUIBBS, Auctioneer. Second Edition, Revised and partly Re-written. Demy 8vo, i2s. 6d. cloth. [Just published. "The position and duties of auctioneers treated compendiously and dearly." Buitder. " Every auctioneer ought to possess a copy of this excellent work." Ironmonger. " Of great value to the profession. . . . We readily welcoma this book from the fact that it treats the subject in a manner somewhat new to the profession." Estates Gazette. Legal Guide for Pawnbrokers. THE PAWNBROKERS', FACTORS' AND MERCHANTS' GUIDE TO THE LAW OF LOANS AND PLEDGES. With the Statutes and a Digest of Cases on Rights and Liabilities, Civil and Criminal, as to Loans and Pledges of Goods, Debentures, Mercantile and other Se- curities. By H. C. FOLKARD, Esq., Barrister-at-Law, Author of " The Law of Slander and Libel," &c. With Additions and Corrections. Fcap. 8vo f 35. 6d. cloth. " This work contains simply everything that requires to be known concerning the department of the law of which it treats. We can safely commend the book as unique and very nearly perfect." Iron. " The task undertaken by Mr. Folkard has been very satisfactorily performed. . . . Such ex- planations as are needful have been supplied with great clearness and with due regard to brevity." City Press. LAND AND ESTATE MANAGEMENT, LAW, etc. 39 Law of Patents. PATENTS FOR INVENTIONS, AND HOW TO PROCURE THEM, Compiled for the Use of Inventors, Patentees and others. By G. G. M. HARDINGHAM, Assoc.Mem.Inst.C.E., &c. Demy 8vo, cloth, price 25. 6d. [Just published. Metropolitan Rating Appeals. REPORTS OF APPEALS HEARD BEFORE THE COURT OF GENERAL ASSESSMENT SESSIONS, from the Year 1871 u> 1885. By EDWARD RYDE and ARTHUR LYON RYDE. Fourth Edition, brought down to the Present Date, with an Introduction to the Valuation (Metropolis) Act, 1869, and an Appendix by WALTER C. RYDE, of the Inner Temple, Barrister- at-Law. 8vo, i6s. cloth. " A useful work, occupying a place mid-way between a handbook for a lawyer and a guide to the surveyor. It is compiled by a gentleman eminent in his profession as a land agent, whose spe- cialty, it is acknowledged, lies in the direction of assessing property for rating purposes." Land Agents' Record. " It is an indispensable work of reference for all engaged in assessment business." Journal of Gas Lighting. House Property. HA NDBOOK OF HO USE PROPERTY. A Popular and Practical Guide to the Purchase, Mortgage, Tenancy, and Compulsory Sale of Houses and Land, including the Law of Dilapidations and Fixtures ; with Examples of all kinds of Valuations, Useful Information on Building, and Suggestive Elucidations of Fine Art. By E. L. TARBUCK, Architect and Surveyor. Fourth Edition, Enlarged, izmo, 55. cloth. " The advice is thoroughly practical." JLa-w Journal. "For all who have dealings with house property, this is an indispensable guide." Decoration. "Carefully brought up to date, and much improved by the addition of a division on fine art, " A well -written and thoughtful work." Land Agent's Record. Inivood's Estate Tables. TABLES FOR THE PURCHASING OF ESTATES, Freehold, Copyhold, or Leasehold; Annuities, Advowsons, etc., and for the Renewing of Leases held under Cathedral Churches, Colleges, or other Corporate bodies, for Terms of Years certain, and for Lives ; also for Valuing Reversionary Estates, Deferred Annuities, Next Presentations, &c. ; together with SMART'S Five Tables of Compound Interest, and an Extension of the same to Lower and Intermediate Rates. By W. IN WOOD, zsrd Edition, with considerable Additions, and new and valuable Tables of Logarithms for the more Difficult Computations of the Interest of Money, Discount, Annuities, &c. , by M. FEDOR THOMAN, of the Societe Credit Mobilier of Paris. Crown 8vo, 8s. cloth. "Those interested in the purchase and sale of estates, and in the adjustment of compensation cases, as well as in transactions in annuities, life insurances, &c., will find the present edition of eminent service." Engineering. &&* ' ' ' Inwoqd's Tables ' still maintain a most enviable reputation. The new issue has been enriched by large additional contributions by M. Fedor Thoman, whose carefully arranged Tables cannot lail to be of the utmost utility." Alining Journal. Agricultural and Tenant-Right Valuation. THE AGRICULTURAL AND TENANT-RIGHT-VALUERS ASSISTANT. A Practical Handbook on Measuring and Estimating the Contents, Weights and Values of Agricultural Produce and Timber, the Values of Estates and Agricultural Labour, Forms of Tenant-Right-Valua- tions, Scales ol Compensation under the Agricultural Holdings Act, 1883, &c. &c. By TOM BRIGHT, Agricultural Surveyor. Crown 8vo, 35. 6d. cloth. " Full of tables and examples in connection with the valuation of tenant-right, estates, labour contents, and weights of timber, and farm produce of all kinds." Agricultural Gazette. " An eminently practical handbook, full of practical tables and data of undoubted interest and value to surveyors and auctioneers in preparing valuations of aH kinds." Farmer, Plantations and Underwoods. POLE PLANTATIONS AND UNDERWOODS: A Practical Handbook oh Estimating the Cost of Forming, Renovating, Improving and Grubbing Plantations and Underwoods, their Valuation for Purposes of Transfer, Rental, Sale or Assessment. By TOM BRIGHT, F.S.Sc., Author of "The Agricultural and Tenant-Right-Valuer's Assistant," &c. Crown 8vo, 35. 6d. cloth. [Just published. " Will be found very useful to those who are actually engaged in managing wood." Bell's Weekly Messenger, " To valuers, foresters and agents it will be a welcome aid." North British Agriculturist. "Well calculated to assist the valuer hi the discharge of his duties, and of undoubted interest and use both to surveyors and auctioneers in preparing valuations of all kinds." Kent Herald, 40 CROSBY LOCK WOOD & SON'S CATALOGUE. JL Complete Epitome of the Laws of this Country. EVERY MAN'S OWN LAWYER: A Handy-Book of the Principles of Law and Equity. By A BARRISTER. Twenty-eighth Edition. Revised and Enlarged. Including the Legislation of 1890, and including careful digests of The Bankruptcy Act, 1890; the Directors' Liability Act, 1890; the Partnership Act, 1890; the Intestates' Estates Act, 1890: the Settled Land Act, 1890 ; the Housing of the Working Classes Act, 1890; the Infectious Disease (Prevention) Act, 1890; the Allotments Act, 1890; the Tenants' Com- pensation Act, 1890; and the Trustees' Appointment Act, 1890; while other new Acts have been duly noted. Crown 8vo, 688 pp., price 6s. 8d. (saved at every consultation ! ), strongly bound in cloth. [Just published. V THE BOOK WILL BE FOUND TO COMPRISE (AMONGST OTHER MATTER) THE RIGHTS AND WRONGS OF INDIVIDUALS LANDLORD AND TENANT VENDORS AND PURCHASERS PARTNERS AND AGENTS COMPANIES AND ASSOCIATIONS MASTERS. SERVANTS AND WORKMEN LEASES AND MORTGAGES CHURCH AND CLERGY, RITUAL LIBEL AND SLANDER CONTRACTS AND AGREEMENTS -BONDS AND BILLS OF SALE- CHEQUES, BILLS AND NOTES -RAILWAY AND SHIPPING LAW BANKRUPTCY AND IN- SURANCEBORROWERS. LENDERS AND SURETIES CRIMINAL LAW- PARLIAMENTARY ELECTIONS- COUNTY COUNCILS MUNICIPAL CORPORATIONS-PARISH LAW, CHURCH- WARDENS, ETC. INSANITARY DWELLINGS AND AREAS PUBLIC HEALTH AND NUISANCES FRIENDLY AND BUILDING SOCIETIES COPYRIGHT AND PATENTS TRADE MARKS AND DESIGNS-HUSBAND AND WIFE, DIVORCE, ETC. TRUSTEES AND EXECU- TORSGUARDIAN AND WARD, INFANTS, ETC. GAME LAWS AND SPORTING-HORSES, HORSE-DEALING AND DOGS INNKEEPERS, LICENSING, ETC. FORMS OF WILLS, AGREEMENTS, ETC. ETC. NOTE. The object of this work is to enable those who consult it to help them- selves to the law; and thereby to dispense, as far as possible, with professional assistance and advice. 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