'UNIVERSITY OF CALIFORNIA. REESE LI ^ \ ,, LIBRARY ; ELECTRO-DEPOSITION A PR A CTTCAL TREA TISE ON THK 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," "THE ART OF SOAP-MAKING," "THE ART OF LEATHER MANUFACTURE," ETC. Wiith imnur0tt0 Illustration* SECOND EDITION, REVISED AND CORRECTED LONDON CROSBY LOCKWOOD AND CO. 7, STATIONERS' HALL COURT, LUDGATE HILL 1887 [All rights reserved] PEEFACE. 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 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 also 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 ; and more especially to Sir Henry Bessemer, to whom he is indebted for an exceedingly interesting com- munication relative to some experiments in depositing copper, made so far back as 1831, or about six years before the discovery of the electrotype process. LONDON, December, 1885. CONTENTS. CHAPTER T. HISTORICAL REVIEW OF VOLTAIC ELECTRICITY. PAGB 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 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 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 Dynamo- electric Machine. Hallett-Elmore Dynamo-electric Machine. Carlyle's Dynamo-electric Machine. Schuckert's Dynamo-electric Machine. Mather's Dynamo-electric Machine. Gulcher's Dynamo- electric Machine. Kapp and Allen'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. Becquerel's Thermo-Pile. Clamond's Thermo-electric Pile. Wray's Thermo-Pile. Noe's Thermo-Battery. The Future of Thermo-Electricity 39 Vlll CONTENTS. CHAPTER IV. HISTORICAL REVIEW OF ELECTRO-DEPOSITION. TAG I? 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 . 51 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. Elcctrotyping by Single-cell Process. Copying Coins and Medals. Moulding Materials. Gutta-percha. Plastic Gutta-percha. Gutta-percha and Marine Glue. Beeswax. Sealing-wax. Siear- ine. Stearic Acid. Fusible Metal. Elastic Moulding Material. Plaster of Paris 91 CHAPTER VIII. ELECTRO -DEPOSITION OF COPPER (continue^. 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 CONTENTS. IX CHAPTER IX. ELECTRO -DEPOSITION OF COPPER (continued). PACK 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, Ac. 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, * ~Z. Z ^ ^ *,' ^~^ 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. Babbing'ton. 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 iluid (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 dcs tasscs (crown of cups) which was exceedingly simple and effective. This consisted of a row of glasses or cups, each containing 7, C z c z c . z c 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 ELECTRICITY. 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. Wcllaston's Battery. An important improvement in the pre- ceding arrangements, but more directly in the battery designed by Dr. Babbington (Fig. 7), was the 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 Battery, 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 BATTEKY. surfaces, but -which may vary in height according 1 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 emploved 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 numerou 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. II, 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 fiat 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. I 1 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 in 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^ 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. I 3 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 electrotyping 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 batteiy 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 maybe 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. Eig. 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 tasscs. 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, coo pairs, which was capable of giving a shock resembling that from the Leyden 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 but little of the quality termed quantity, and therefore represents current electricity in its weakest form. Leclanche 7 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. The 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 HISTOKICAL 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 1 -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 time after its separation from Fig. 17. the poles of the battery, provided that the insulation were maintained. This is termed polarisation. The subject was afterwards further investi- gated, but no practical application of the fact seems to have taken SECONDAKY BATTEKIES. 17 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. Hallett-Elmore Dynamo-electric Machine. Carlyle's Dynamo- electric Machine. Schuckert's Dynamo-electric Machine. Mather's Dynamo - electric Machine. Giilcher's Dynamo - electric Machine. Kapp and Allen's Dynamo-electric Machine. Oersted's Discovery. In the year 1819, Professor Oersted, of Copen- hagen, made the important discovery that magnetism could be 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 THE GALVANOMETER. Fig. 18. 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. There is not stronger evi- dence of the development 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 fundamenta discovery, is that an electrified wire not only possesses the power of turning the magnetic needle from its natural position, but it can also 20 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 Ritchie, its sensi- 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 Fig. 20. bility is further increased. 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. 21. 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 HAGNETO-ELECTKIC1TY. 21 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,'f or 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 induced magnetism, to distinguish it from the permanent magnetic condition of steel bar or horse-shoe magnets with which all are familiar. "We &' 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 armature. 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-ELECTBICITY. 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 poles, 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. &c. 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 *, 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 the works of the Electro -metallurgical Company. Wilde's Bftagneto-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 Sheflield and Birmingham. This machine deposits about 30 ounces of silver per hour, with an expenditure of J 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 GRAMMES MAGNETO-MACHINE. 27 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. 28 MAGNETO-ELECTRICITY. 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-ELECTBICITY. 29 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*0 Total height -6 metre. Total width -55 Deposits silver per hour 600' grammes. Kequired power to work ii 50* kilogramrnetres. Dynamo-Electricity. After the introduction of Wilde's Magneto- electric Machine in 1866, 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 con version 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, J 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 Txpox^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. { Proceedings of the Royal Society, vol. xv. p. 397. 3O DYNAMO-ELECTBICITY. 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 machine, 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. 31 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 J.' 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^ horse-power. A machine suitable for silver-plating, coppering iron, &c., works through a 32 DYNAilO -ELECTRICITY. 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. "VVeston'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 THE HALLETT-ELMORE DYNAMO-MACHINE. 33 and taking 1 care that no obstacle should be thrown in the way, he suc- ceeded in securing 1 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 current at the cost of less than one horse-power. There can be no doubt what- ever that the remarkable development of nickel-plating in this country and in America, as also the substitution of electrotyping for the stereotype process in American printing establishments, are greatly, if not chiefly, due to the introduction of the Weston dynamo -electric machine. The advantages claimed for "Weston's dynamo -electric machine, which is shown in Fig. 29, are : the use of an iron ring or shell to which all the magnets are attached ; one circuit and one shaft only are used, dispensing with the use of extra commutators and brushes ; the currents from all the armatures are picked up by two brushes and sent round the electro -magnets. The armatures are constructed entirely of iron ; the commutator is made in a very simple manner, in only two pieces, and is outside the bearings ; the parts liable to be injured by dirt and oil are protected by a cover ; the parts subject to wear are interchangeable, and can be replaced in a few minutes ; it is about half the size and weight of any other machine of equal power. The steel plates on the electro -magnets are a novel and important invention, and prevent the current from the vats reversing the direction of the current while the machine is running ; the machine is so powerful that it only needs to be run at from 450 to 800 revo- lutions. The inventor also states that "the use of one circuit is a very important matter, since it not only saves much power, wear on the machine, the use of two commutators, and four brushes, besides much injury to the same, but also secures an almost perfect self -regu- lating machine the current generated depending upon the surface of the work in the solutions." We understand that these machines, of considerable size, are being used for various electrolytic operations in the United States. The Hallett-Elxnore Dynamo-electric Machine. This machine, which is a combination of two inventions patented respectively by Mr. Shackleton Hallett, Founder of the Electrolytic Company, Black- friars' Road, London, and Mr. William Elmore, has been adopted by some large firms for the general purposes of electro -deposition, as also by the Government in several departments. The larger type of machine, which is represented on next page, is being successfully applied to coating large pieces of machinery with copper, such as the hydraulic rams used in connection with the recoil machinery of the D 34 DYNAMOELECTKICITY. great guns of the British fleet, to protect them from the action of sea -water. These rams range from 6 to 10 feet in length and are from 6 to 1 8 inches in diameter. The large machine is also used for coppering iron cylinders for calico printers' rollers, for ships' pro- peller shafts,* for producing large electrotypes for ordnance maps, &c. * These propeller shafts are usually coated with gun-metal sheathing, cast CAKLYLE S DYNAMO-MACHINE. 35 The illustration, Fig. 30, represents a 24 -inch, machine, and is con- structed, Mr. Elmore states, to deposit three tons of copper upon regular surfaces, as in copper refining, in six days (144 hours). In practice the machine has been found to deposit upon irregular surfaces about 1 1 ton of copper per week. The electromotive force of this machine is less than two volts, and is frequently worked as low as one volt by diminishing the speed of the armature. A chief feature in the construction of the large machine is in the arrangement for cooling the magnets, and also such parts of the machine as would be liable to become heated by friction. This is effected as follows : A constant stream of water passes through a stuffing-box fixed upon the pillar or upright at the back of the machine, and from thence into the hollow between the dome and the disc carrying the armature magnets ; it then passes through each of the cores of the magnets, and out at the back of the second dome, Fig. 31. Carlyle's Dynamo-electric Machine. finally making its exit at the front of the machine. By this system of cooling the armature and magnets, the machine keeps uniformly cool and steady in action, even when running at high speed. Carlyle's Dynamo - electric Machine. This machine, an illus- tration of which is given in Fig. 3 r , appears to be of the Weston type, but we are unable to furnish any particulars as to its capa- bilities. upon the steel core ; but, in time, the sea-water acts upon the alloy, forming a hollow, or groove, all round, until, eventually, the shaft is liable to break from this cause ; the electro-deposited copper, which is perfectly pure and adherent, is believed to resist the action of the sea-water more effectually than gun-metal. 30 DYNAMO-ELECTRICITY. Schuckert'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 electro typing, at Messrs. Cassell and Co.'s, Ludgate Hill, London, which we were informed gave perfect satisfaction. While almost noiseless in action, it presented the ap- pearance of being an exceedingly well -construe ted machine. We understand that the more closely the maker follows the original design of the inventor, the greater is the practical value of the machines. The larger type of this dynamo is shown in Fig. 32. By winding the bobbin and the coils of the electro -magnets with a finer Fig. 32. Schuckert's Dynamo electric Machine. wire, the number of volts may be increased two, three, or fourfold, without altering the power or the speed of the 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. Gulcher's Dynamo -electric Machine. This machine, which is manufactured by the Giilcher Electric Light Company, of Battersea, GULCHER DYNAMO-ELECTRIC MACHINE. 37 London, has hitherto been more especially constructed for electric lighting- ; but we understand that the Company have lately turned their attention to the construction of these machines for electrolytic copper refining-. Indeed, we are informed that a large machine of this type is now being adopted by a well-known firm in Swansea for this purpose, and is giving- great satisfaction. We think it probable, from information which has reached us, that the large Giilcher machine, an illustration of which is given below, will shortly become an important addition to our electrolytic machinery. Fig- 33- Giilcher's Dynamo-electric Machiue. Kapp and Allen's Dynamo-electric Tachine. This dynamo, designed by Mr. Gisbert Kapp, is an exceedingly well -constructed machine of the Gramme type, but possessing some important features due to the ingenuity of the inventor himself, who has had considerable experience in this branch of electric engineering. In the construction of this machine, an unusually powerful magnetic field is obtained by the employment of curved electro -magnets, which have also the addi- tional advantage of occupying but little space. The core of the armature consists of charcoal iron wire wound in sections upon a per- forated gun -metal cylinder, the sections being insulated from each other, and separated by air spaces, for the purpose of keeping the cylinder and other parts cool. When in motion, the cylinder, in fact, plays the part of a fan. " Radial projections, or driving horns, are 38 DYNAMO-ELECTRICITY. cast at even intervals, around the supporting cylinder, and their tips, which are provided with fibre ferrules, enter between the external coils of the conductor on the armature, and transmit in a positive and mechanical manner the driving power into these coils, which do the work. The supporting cylinder is keyed to the axis by two sets of spokes and central hubs, and the inner and outer circumference of the core is left free from winding to allow ingress and egress of air. The commutator is of the usual type, and a double set of brushes is em- ployed, so that any brush may be exchanged without interrupting- the current." These machines have hitherto been devoted to the purposes of electric lighting ; but we understand that it is in con- templation to construct them specially for electrolytic purposes. 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. BecquereFs Thermo-Pile. Clamond's Thermo-electric Pile. Wray's Thernio-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, b, 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 THEEMC-ELECTEICITY. 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-ELECTRIC SERIES. Galena. Bismuth. Mercury) Nickel J Platinum. Palladium. Cobalt l Manganese]" Tin. Lead. Bras?. Rhodium. Gold. Copper. Silver. Zinc. Cadmium. Charcoal. Plumbago. Iron. Arsenic. Antimonv. Dr. Matthiessen arranged the following order and electric energy ofjvarious bodies for temperatures usually ranging between about 40 and 100. In the table the electromotive force of the thermo- current THERMO-ELECTRIC LAWS. excited between silver and 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 -f- 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 OKDER OF METALS. Bismuth, commercial pressed wire 35' Sl *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'O94 ^Mercury 2-524 Aluminium 1*283 Magnesium I-I 75 *Lead, pressed wire . . . 1*029 *Tin, pressed wire .... rooo Copper wire 1*000 Platinum 0-723 Iridium 0-163 *Aptimony, pressed wire . . 0*036 *Silver . . 0*000 Gas coke, hard 0*057 *Zinc. pressed wire .... 0*208 ^Copper, voltaic * .... 0*244 ^Cadmium 0*332 Antimony, pressed wire . . 1*897 Strontium 2*028 Lithium 3*768 * 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 . . . f I 3' 6 7 Alloy, 2 antimony . . . j i zinc, cast . . .J 22 ' 7 ^Tellurium 179*80 ^Selenium 290-0 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 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 Piles 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 36' and uniform sweep, by which the respec- tive couples were securely and perfectly united with little or no accident when the hand had become accus- tomed to the manipulation. It maybe 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 THEKMO-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 THERMO-PILE. 45 a four-winged fan (c] of simple construction, set in motion by a pulley (d) 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 File. 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* : " 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-ELECTKICITY. 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 bass 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, prevent contact, except at the junction. The number of radial Fig. 40. Fig. 39- 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-ELECTEICITY. 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 diamond'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 NOE 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 thermp-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. Noe, of Vienna, consists of a series of small cylinders, about 1 1 inch in length, and f 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 tli 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 electrotyping. 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. 50 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 thermo-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, so 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 HISTOKICAL EEVIEW OF ELECTEO-DEPOSITIOX. 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. G-olding Bird, who decomposed solutions of the chlorides of ammonium, potassium, and sodium, and succeeded in depositing these metals upon a negative electrode of mercury, f 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-. R. Elkington, 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. K. 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 Athenaum, 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 land 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 this 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 HISTOEICAL EEVIEW 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 -gth 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 PAPER ON ELECTROTYPING. 57 11 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 ME. BIKCKS ON JOEDAIs's LISCOVERY. 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' a 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 in 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 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 up wards, 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 70, 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, ' ' 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. Golding 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. Golding Bird's Experiments. There can be no doubt what- ever that after Dr. Golding 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. Golding 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 IB clear now, however, that Dr. G-olding 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 were 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 HISTOKICAL EEVIEW OF ELECTRO-DEPOSITION. 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 clcctrography , 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 showed 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 DIKCKS 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 hitter 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 DIRGES ON SPENCER'S CLAIM. 67 late Dr. Andrew Ure to Mr. Dircks snows how fully he recognised that gentleman's advocacy of Jordan'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 kindness 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 f or 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 we transcribed from the originals, are now, we believe, published for the first time. 68 HISTORICAL BEVIEW OF ELECTEO-DEPOSITION. pened 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. Elkington 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 Daniell 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 DIKCKS 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. R. 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 the 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, "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. 7 1 free ends of the conducting wires of a voltaic battery, generally termed the positive and negative poles, are those suf aces 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 r\\iKTpov and odos, a way, thereby signifying that substance or surface, ivhether 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, downwards, odog, a ivay], 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 pass 72 THEOKY OP ELECTKOLYSIS. 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 siibstance 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. Tig. 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 iveight, 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. ELECTROLYSIS OF SULPHATE OF COPPER. 75 Fig. 47. 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 ist 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 nil 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 (now 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 Pig. 49. A solution of ' ~ **^J*^\ ddS^^fch '* sulphate of potash was placed in contact with the negatively electrified point, pure water was placed in contact with the positively electrified point, and p- a weak 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 ILLUSTRATIONS 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. Fig. 51- 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 (a, 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 OP ELECTROLYTIC THEORY. 79 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 blue. CHAPTER VI. 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., &c. ; revised edition by W. H. Preece, M.I.C.E. ; and Fleeming Jenkin's " Treatise on Electricity and Magnetism." V ,Y)J CONDUCTORS AND INSULATORS. 8 1 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 carbonate 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 ^ 6 - 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 .... loo-o Copper .... 99'9 Gold .... 77-9 Zinc .... 29-0 Cadmium . . . 237 Palladium . . . 18*4 Platinum . . . 18-0 Cobalt .... 17-2 Nickel . . . 13' i Tin .... 12-4 Thallium . . . 9-2 Lead . . . .8-3 Arsenic . . . .4-8 Antimony . . .4-6 Mercury . . . r6 Bismuth . . .1-2 Graphite . . . -069 Gas Coke . . . "038 Bunsen's Coke . . -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 -fa 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 denned 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. 8 4 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 stratujm of liquid 4 inches wide and I inch thick had to be traversed by the current, in the second arrangement it has to Fig- 52. 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 not 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 F to denote the actual force of the current, that is its power to produce heat, magnetism, chemical action, &c., E the electromotive force, and B the resistance, of the wires and electrolytes, then -tf E r = R' 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 resistance. 2. The resistance in any circuit is found by dividing the value of the E.M.F. by the value of the current. t American Electrician. 86 ELECTRICAL THEORIES. 3. The E.M.F. in any circuit is found by multiplying the vahie 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 follows 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. 8 7 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 = TOO. Silver at 2I2 = IOO. Each metal com- pared with itself at 32= 100. Silver (hard drawn) . . Copper (hard drawn) . . Gold (hard drawn) . . . Zinc At 32 lOO'OO 99'95 77-96 29'02 23'72 17-22 16-81 13-11 12-36 9'i6 8'32 4-76 4-62 i '245 At 21 2 7I-56 70-27 55-90 20-67 16-77 8-67 5-86 333 3'26 0-878 lOO'OO 98-20 78-11 28-89 23-44 I2'I2 8-18 4-6 5 4'55 1-227 71-56 70-31 71-70 71-23 70-70 7o' 1 1 68-58 70-39 69-88 70-54 70-5I Loss p. c. 28-44 29-69 28-30 28-77 29-30 29-89 31-42 29-61 30' 1 2 29-46 29-69 Cadmium Cobalt Iron (hard drawn) . . . Nickel Tin Thallium Lead Arsenicum Antimony Bismuth . 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, its electromotive force is given in volts, its resistance in ohms, and its quantity or strength is given in amperes ; thus, a machine for depositing copper (which does not require a current of high tension) may have an electromotive force of I or 2 volts, with a resistance of 0-5 ohm, and a current of 800 or 900, or more amperes. We lately heard of a machine giving a force of 1,500 amperes. 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 * "Philosophical Transactions," 1858 and 1862; and " Proc. Koy. Soc.," vol. xii. p. 472. 88 ELECTRICAL THEORIES. other words, a Daniell cell is a little more than a volt, the determina- tions of it value by different experimentalists being as below : Werner Siemens noSvolt. Latimer Clark 1*079 Sir W. Thomson roi2 F. Kolrausch 1*138 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 ELECTEOMOTIVE FORCE OF BATTERIES. Name of 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 (i : 12) J 0-719 De la Rive. Smee .... Amalgamated zinc in | sulphuric acid, plati- nised silver, or plati- num in sulphuric acid (i : 12) 1-098 1-107 0-541 1*192 Clark and Sabine. Sprague. De la Rive. Naclari. ( Daniell . . \ Amalgamated zinc hf sulphuric acid (1:4); copper in saturated so- lution of copper sul- phate 1-079 1-079 1-079 1-079 Clark and Sabine. Sprague. De la Rive. Naclari. I Zinc in dilute sulphuric " acid (i : 12) ; "copper in saturated solution 0-978 0-98 Clark and Sabine. Du Moncel. ( Zinc in sal-ammoniac ; " 1-481 ; Clark and Sabine- carbon with manganese peroxide in sal-ammo- 1*561 1 1-942 Sprague. De la Rive. Leclanche . . -> niac Zinc in solution of com-"^ mon salt ; carbon with manganese peroxide in f common salt solution J 1-259 i '493 1-360 i '34 Beetz. Sprague. JNaclari. Du Moncel. Mari6-Davey . Zinc in dilute sulphuric ( acid (i : 12) ; carbon \ in mercurous sulphate I 1*524 i*542 1-482 1-440 Clark and Sabine. Sprague. Naclari. Du Moncel. Zinc in dilute sulphuric""! acid (i : 12); platinum \ 1*956 Clark and Sabine. Grove. . . .- in fuming nitric acid J Zinc in dilute sulphuric^ acid (1:12); platinum I i'524 Clark and Sabine, in nitric acid of 1-38 \ i'542 Sprague. sp. gr. ELECTEOLYTIC CLASSIFICATION OF ELEMENTS. 89 TABLE OF ELECTROMOTIVE FORCE (continued). Name of Element. Constitution. Electro- motive Force in Volts. Authority. r Zinc in dilute sulphuric^ acid (i : 12) ; carbon V in fuming nitric acid j 1-964 i '95 Clark and Sabine. Du Moncel. Bunsen . . . Zinc in dilute sulphuric^] 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. Zinc in dilute sulphuric^) acid (i : 12) ; carbon ', 2-028 Clark and Sabine. I in bichromate of potas- ! sium J 1-905 2'120 Sprague. Naclari. Grenet . . . Zinc and carbon in bi- V chromate of potassium / 25 JN aclari. 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 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," 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, electro typing 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 more 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 f| 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 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 Fig. 54- 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 stoat to bear re- 94 ELECTRO-DEPOSITION OF COPPER. 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 of 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 after- 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 been recom- mended by Gore : 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 g 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 i| Another formula consists of : ozs. White Wax 8 Stearine 3 Flake White or Litharge .... J 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. OZ3. 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 COPPEK. 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, plumbago, 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 of copper from taking place on the upper edge (beyond the actual impression), the plumbago which has been accidentally brushed over this surface should be removed, which may be conveniently done by rubbing it off with a piece of damp rag placed over the forefinger. The mould is now to be attached to the conducting wire by gently heating its longer end in the flame of a candle or ignited match, and then placing it on the edge of the mould, as far as the circumference of the impression ; by giving it gentle pressure it will become sufficiently imbedded ; the wire must not, however, be below the flat surface of the mould. If held steadily in the hand for a few moments, or until the wire and gutta-percha have cooled, the joint will set, and the mould may then be carefully laid aside until the point of junction has set firm. A little plumbago must now be brushed over the joint, so as to ensure a perfect electrical connection between the wire and the plumbagoed mould. The mould being attached to the conducting wire, must now be connected to the zinc by its binding -screws as before (Fig. 54), and both should be immersed at the same time in their respective solutions, but this must be done with care, otherwise the mould may become separated from the wire. It may be well, in this place, to call attention to certain precautions which, if carefully followed, will prevent failure, and consequent disappointment, in electrotyping. Precautions. I. The solution of copper to be used in the single-cell apparatus must be kept as nearly as possible in a saturated condition, which is effected by keeping the shelf or tray constantly supplied with crystals of sulphate of copper. 2. The superficial surface of zinc immersed in the porous cell should not be much greater than that of the mould to be copied. 3. The solution should be stirred with a * Commonly called blacklead, but in reality carbon in a crude state. BRONZINtt THE ELECTROTYPE. IOI glass rod or strip of wood before immersing the mould, especially if it has been previously used for electrotyping ; if this is not done, the deposit may become irregular in thickness. 4. The plumbagoed mould should not be disturbed until its entire surface is covered with copper. A few moments after immersion, a bright pinkish red deposit of copper will be observed at the end of the wire, which in a short time will radiate in the direction of the plumbagoed surface, and this will gradually extend wherever this conducting medium has been spread with the brush, provided the operation has been con- ducted with proper care, and an uniform coating obtained. Treatment of the Electrotype. A sufficiently stout deposit of copper, upon a gutta-percha mould of a small coin, may generally be obtained in about two days, or even in less time, under the most favourable conditions ; but it is not advisable to attempt to separate the electrotype from the mould while the deposit is very thin, other- wise the former may become broken in the operation. Assuming the deposit to be thick enough, the first thing to do is to cut the end of the wire connected to the mould with a pair of cutting pliers or a file, after which the superfluous copper may be removed from the outer edge by breaking it away with the pliers, taking care not to injure the " type " itself. The mould may then be placed in hot water for a moment, when the electrotype will readily separate from the gutta- percha. In order to give additional solidity to the electrotype, it should be lacked up with pewter solder, which may easily be done as follows : Put a small piece of zinc into about a teaspoonf ul of hydrochloric acid (muriatic acid) ; when the effervescence which takes place has ceased, brush a little of the liquid, which is a solution of chloride of zinc, over the back of the electrotype, and then apply solder by means of a moderately-hot soldering iron, until the entire surface is tinned, as it is called, when a further supply of solder should be run on to the back to give the required solidity. When this is done, the rough edge of the electrotype should be rendered smooth with a keen file. Bronzing the Electrotype. To impart an agreeable bronze ap- pearance to the type, it should first be cleaned by brushing it with a solution of carbonate of potash (about half a teaspoonf ul in an ounce of water), and applying at the same time a little whiting. An ordinary tooth-brush may be used for this purpose, and after brisk rubbing the type must be well rinsed in clean water. The bronze tint may be given by brushing over it a weak solution of chloride of platinum (i grain to an ounce of water) ; when the desired tint is obtained, the type is to be rinsed with hot water and allowed to dry. The tone may be varied from a delicate olive -brown to deep black, according to the proportion of platinum salt employed. A few drops of sulphide of ammonium in. water, or, still better, a few grains of IO2 ELECTRO-DEPOSITION OF COPPER. sulphide of barium dissolved in water, will give very pleasing- bronze tints to the copper surface, the depth of which may be regulated at will by a longer or shorter exposure to the action of the bronzing material. If a solution of sulphide of barium be used, about 5 grains to the ounce of water will produce a pleasing tone in a few seconds. It is better to immerse the electrotype in the liquid (previously filtered) and to remove it the instant the desired tone is reached, and to place it at once in clean water. Another method of bronzing electrotypes is by the application of plumbago, by which very pleasing effects may be obtained with a little care in the manipulation. The surface of the electrotype is to be first cleaned with rotten stone and oil ; the oil is then to be par- tially removed by a tuft of cotton wool, and the surface is next to be brushed lightly over with plumbago (a soft brush being used) until a perfectly uniform coating is given. It is next to be heated to a point that would singe the hair of the blacklead brush, and then set aside to cool, after which it must be brushed with considerable friction. The tint will depend upon the quantity of oil allowed to remain, this enabling the surface to retain more of the blacklead, consequently to appear of a darker colour. The effect is very fine, and gives high relief to the prominent parts, from their getting so much more polish than the hollows, thus obviating the disagreeable effect which all unbronzed bassi-relievi produce by reason of their metallic glare. Hockin. The beautiful red bronze tone which is seen on exhibition and other medals is produced by brushing over the medal a paste composed of peroxide of iron (jewellers' rouge) and plumbago, after which the article is moderatly heated, and when cold is well brushed until it acquires the necessary brightness and uniformity of surface. Equal parts of fine plumbago and jewellers' rouge are mixed up into an uniform paste with water, and the cleaned medal is then uniformly brushed over with the mixture, care being taken not to allow the fingers to come in contact with the face of the object. The medal is then placed on a stout plate of iron or copper, and this is heated until it acquires a dark colour ; it is then removed from the fire and allowed to become cold. It is next brushed for a long time, and in all directions, with a moderatly stiff brush, which is frequently passed over a block of yellow beeswax, and afterwards upon the paste of plum- bago and rouge. The bronzing may also be produced by dipping the cleaned medal in a mixture composed of equal parts of perchloride and pernitrate of iron ; the medal is then to be heated until these salts are thoroughly dry. It is afterwards brushed as before with the waxed brush until a perfectly uniform and bright surface is obtained. Bronzing may also be effected by dipping the medal in a solution of COPYING PLASTER OP PARIS MEDALLIONS. 103 sulphide of ammonium, and when this has dried, the plumbago and rouge paste is to be applied as before, and the waxed brush again employed. If the object be heated after applying the sulphide of ammonium, a black bronze, called " smoky bronze," is produced, and if the high lights be lightly rubbed with a piece of chamois leather dipped in spirit of wine, a very pleasing effect of contrast is obtained. Moulds of Sealing Wax. This material is, as we have said, very useful for obtaining impressions of seals, signet rings, and other small objects. A simple way of taking an impression in sealing-wax is as follows : Hold a card over a small benzoline lamp, but not touching the flame ; now take a stick of the best red sealing-wax and allow it to touch the heated part of the paper, working it round and round until a sufficient quantity of the wax becomes melted upon the card. Now place the card upon the table, and having gently breathed upon the seal or signet ring, impress it in the usual way. Having secured an impression, cut away the superfluous portions of the card with a pair of scissors, and moisten the wax impression with a few drops of spirits of wine. When this has apparently dried, proceed to brush plumbago over the surface, using a camel-hair brush, and when perfectly coated, gently heat the end of the conducting- wire and apply it to the edge of the sealing-wax, allowing the point of the wire to approach the edge of the impression. Now brush a little plumbago on the point, and connect the short end of the wire to the binding- screw. After having obtained several electrotypes successfully, and thereby become au fait to the manipulation of the single-cell apparatus, the student will naturally desire to extend operations to objects of a more important nature, such as medallions, busts, statuettes, and natural objects, as leaves, fishes, &c. But before attempting the more elabo- rate subjects it will be well to select, for our next operation, one of a simpler character, such as a plaster of Paris medallion, an admirable model to reproduce in metallic copper. Copying Plaster of Paris Medallions. These pleasing works of art, which may be obtained at small cost from the Italian image makers, are specially suited for the elementary study of the electrotype process, while a cabinet collection of such objects reproduced in copper forms an exceedingly interesting record of the manipulator's skill and perseverance. There are several materials from which moulds from plaster medallions may be obtained ; but we will first describe the method of preparing a mould with gutta-percha. To render the plaster more capable of bearing the treatment it will have to be sub- jected to, the face of the medallion should first be brushed over with boiled unseed oil, and this allowed to sink well into the plaster. After about two days the oil will have sufficiently dried and hardened upon IO4 ELECTRO-DEPOSITION OF COPPER. the surface to render the plaster less liable to injury. The medallion thus prepared is next to be provided with a rim or collar of pasteboard or thin sheet tin, which must be tightly secured round its circumference either by means of thin copper wire, jeweller's "binding- wire," or strong twine. The rim should project about half an inch above the highest point on the face of the medallion, and must be on a level with its base ; it is then to be laid upon a perfectly smooth surface until the moulding material is ready. We recommend the student to prac- tise upon small medallions at first ; say about two inches or two inches and a half in diameter. Preparing the Mould. A lump of gutta-percha is now to be taken of sufficient size to cover the medallion, fill the vacant space up to the top of the rim, and project above it. The gutta-percha is to be softened in hot water and rolled up into the form of a ball, as before directed, care being taken to obliterate all seams or cracks by repeatedly soaking in the hot water and rolling in the hands. It must on no account be applied until it is perfectly smooth, and as soft as hot water will make it. To give additional smoothness to the surface of the ball, it may be lightly rolled round and round, with one hand only, for an instant upon a polished table just before being used. Now take the ball in one hand and place it in the centre of the medallion ; then press it firmly from the centre towards the circumference, taking care not to shift it in the least degree. The gutta-percha must be pressed well into the cavity, and when this is done, a piece of flat wood may be placed on the mass and this pressed with both hands with as much force as possible for a few moments, when it may be left until the gutta-percha has set hard. If convenient, a weight may be placed upon the board after having pressed it with the hands. In about half an hour the board may be removed, and the mould allowed to rest until quite cold, when the rim may be removed and the mould sepa- rated by gently pulling it away from the medallion. As a precaution against breaking the plaster medallion, it may be well to suggest that its back should be examined, and if it be otherwise than perfectly flat, it may be advisable to gently rub it upon a sheet of glass-paper, which will readily remove all irregularities from the surface. It is also important that the surface upon which the medallion is laid, when applying the gutta-percha, should be quite level ; and it will be still better if several folds of blotting-paper are placed between the table and the medallion before the necessary pressure is given. These points being attended to, there is little fear of the medallion becoming broken. Plumb agoing. The gutta-percha mould is now to be well plum- bagoed, for which purpose a soft brush, such as jewellers use for brushing plate and jewellery that has been rouged, may be used, and CLEARING THE MOULD. I 05 this being frequently dipped into the plumbago is to be lightly but briskly applied, special care being taken to well plumbago the hollows. "When it is borne in mind that the most delicate line, even if imper- ceptible to the eye, will be reproduced in the metallic copy, the importance of not injuring the face of the mould will become at once apparent. It is also absolutely necessary that the gutta-percha should be of the best quality, and since the same material may be used over and over again, its first cost is of little consideration. Clearing the Mould. The mould being well coated with plum- bago, all excess of this material which has become spread over the outer edges, beyond the impression itself, must be wiped away, and the more completely this is done the less trouble will there be after- wards in clearing away from the electrotype the crystalline deposit which, under any circumstances, forms around the circumference of the electrotype. Indeed, when the student has once or twice experienced the inconvenience of having to remove the superfluous copper from his electrotypes, he will not fail to exert his wits to diminish the labour which this involves as far as practicable, by every possible care before the mould goes into the copper bath. We therefore urge for his guidance, that the removal of the excess of plumbago should be deemed one of the important details of his manipulation, and that it should never be neglected. After wiping away the excess of blacklead, it will be found a good plan to place a piece of dry rag on the forefinger and to rub it on a common tallow candle, so as to make the part slightly greasy ; if now the edge of the mould (carefully avoiding the impres- sion) be rubbed with the rag- covered finger, this will effectually prevent the deposit from taking place upon such part ; before doing this, however, the Conducting wire should be gently heated and im- bedded in the edge of the mould as before, taking care that the point of the wire touches the extreme edge of the impression, and a perfect connection between the wire and the latter must be secured by apply- ing a little plumbago with a camel-hair brush or the tip of the finger. It is sometimes the practice to apply varnish of some kind to the edges of moulds, and also to the conducting wire as far as the joining, but until the student has thoroughly mastered the process of copying simple objects in the way we have indicated, we do not recommend him to employ varnishes ; indeed not until dealing with objects of a larger and more elaborate kind. The mould being now ready, is to be connected to the binding- screw by its wire, and since the material of which it is composed is much lighter than the copper solution, the wire must be sufficiently rigid, when bent at right angles, as in Fig. 54 to keep the mould well down in the bath. Being placed in the solution, it must be allowed to remain undisturbed until the entire surface of the impression is io6 ELECTKO-DEPOSITION OF COPPER. covered. In from two to three days the deposit should be of sufficient thickness to allow of its separation from the mould. For copying small medallions of the size referred to, the single -cell apparatus shown in Fig. 54 may be used, but for larger sizes or for depositing upon several moulds at the same time, the arrangement shown in Fig. 55 will be most suitable. This apparatus consists of a wood box well varnished in the interior, and divided into two cells or compartments by a partition of thin porous wood. The larger cell is nearly filled with a satu- rated solution of sulphate of copper, and the smaller cell with a half -satu- rated solution of sal-ammoniac. A perforated shelf is suspended in the larger compartment to contain a supply of crystals of the sulphate. A plate of pure zinc, connected by a copper conducting wire, is suspended in the smaller cell, and the mould connected to the opposite end of the wire by suitable binding -screws. In this ar- rangement neither acid nor mercury are used, and although the action is not so rapid as in the former arrangements, it is very reliable for obtaining good results. Wax Moulds from Plaster Medallions. Beeswax is a very useful material for preparing moulds from plaster medallions, the following simple method being adopted : The medallion, instead of being oiled as in the previous case, is simply soaked in hot water for a short time or until it has become completely saturated. First put a sufficient quantity of wax into a pipkin and melt it by a slow fire ; when melted, place it on the hob until wanted. Place the medallion face upwards in a plate or large saucer, into which pour boiling water until it reaches nearly half-way up its edge. In a minute or two the face of the plaster will assume a moist appearance, when the excess of water is to be poured out of the plate. A rim of card is now to be fastened round the edge of the medallion, which may be secured either by means of sealing-wax or a piece of twine. As before, the rim should extend about half an inch above the most prominent point of the image. The medallion being returned to the plate, the wax is now to be steadily poured on to the face of the object, the lip of the pipkin being placed near the pasteboard rim and nearly touching it, to prevent the formation of air-bubbles. When the cavity is filled up to 55- WAX MOULDS FROM PLASTER MEDALLIONS. 1 07 the top of the rim, if any air-bubbles appear they must be at once removed with a camel-hair brush kept for this purpose, or the feather end of a quill, or even a strip of paper may be used. The wax must now be allowed to cool as slowly as possible, and in order to favour this gradual cooling, a clean, dry jar may be inverted over the mould and there left until the wax is quite cold. This precaution will tend to prevent the wax from cracking, an event which sometimes, but not very frequently, occurs. When quite cold, the wax mould will generally separate from the plaster by the application of moderate force to pull them asunder. If such is not the case, however, return the medallion to the plate and pour in a little boiling water. After a few seconds' immersion the mould will easily come away. If, however, owing to some irregu- larity in the face of the medallion, the mould still refuses to separate, plunge the whole into cold water, and, if necessary, use the edge of a knife as a lever between the two surfaces and force them asunder. If it be found that small portions of plaster adhere to the mould these may be carefully picked out with a fine-pointed piece of wood, and the mould afterwards very lightly brushed over with a soft plate brush. Should it be found that some particles still obstinately adhere to the wax, apply a little oil of vitriol with a thin strip of wood to the parts and set the mould aside for about twelve hours, by which time the acid, by attracting moisture from the air, will loosen the plaster, which may then be brushed away with a soft brush and water. The mould must then be put away to dry, or may be laid, face downward, upon a pad of blotting-paper or calico. The mould is now to be plumbagoed with a very soft brush, but, owing to the yielding nature of the wax, the greatest care must be taken not to apply the brush too severely, only sufficient friction being used to coat the surface uniformly. It is a good plan to sprinkle a little plumbago over the face of the mould, and then to work the brush about in circles, by which means a well plumbagoed surface may readily be obtained. This operation being complete, the super- fluous plumbago is to be brushed off, and, by blowing upon the face of the mould, any plumbago remaining in the crevices may be re- moved. The conducting wire is to be attached, as in the case of gutta-percha, by gently warming the end of the wire ; but, if the mould be a tolerably large one (say, 3 inches in diameter) it will be well to bend the end of the wire so as to leave a length of about an inch or more to be embedded in the edge of the mould, by which means it will be more effectually supported than if the point of the wire only were attached. The joint must now be well plumbagoed, and the excess of this material which has been brushed over the edges may easily be removed by scraping it away with a pen-knife. IO8 ELECTKO-DEPOSITION OF COPPEK. The same precautions must be observed with regard to wax-moulds as with those made from gutta-percha when immersing them in the bath, otherwise they will, from their exceeding lightness, be disposed to rise out of the solution. In the case of large moulds made from such light materials they require to be weighted in order to keep them beneath the surface of the copper solution, as we shall explain when treating of them. The stearine composition may be employed instead of wax in the preceding operation, but we recommend the student to adopt the latter material for copying small medallions, since, with a little care, it will answer every purpose, and needs no preparation beyond melting it. Moulds from Fusible Metal. There are many ways of making moulds from fusible metal, but, for our present purpose, we will select the most simple. To obtain an impression of a coin or medal, melt a sufficient quantity of the alloy in a small ladle or iron spoon, then, hold- ing the coin face downward between the forefinger and thumb of the right hand, pour the alloy into the rim of an inverted cup or basin, and, bringing the coin within a distance of about 2 inches from the molten alloy, allow it to fall fiat upon the metal and there leave it until cold. If, when the metal is poured out, there is an appearance of dulness on the surface (arising from oxidation of the metals) a piece of card or strip of stiff paper should be drawn over it, which will at once leave the surface bright. As the metal soon cools, how- ever, this may be more conveniently done by an assistant just before the coin is allowed to fall. If no other help is at hand a piece of card should be placed close to the cup, so that the moment the metal is poured out it may be applied as suggested, and the coin promptly dropped upon the cleaned surface of the alloy. A very little practice will render the student expert in obtaining moulds in this way, and, considering how very readily the material is re-melted, a few failures need not trouble him. The fusible alloy may also be employed in the form of a paste, but, in this case, it is advisable to have the assistance of another pair of hands, since, in this condition, it soon becomes solid and therefore un- usable. The coin should first have a temporary handle attached to it, which may readily be done by rolling a small lump of gutta-percha into the form of a ball ; one part of this should now be held in the flame of a candle until the part fuses, when it is to be pressed upon the back of the coin and allowed to remain until cold. This gutta- percha knob will serve as a handle by which the coin may be held when the impression is about to be taken. The requisite quantity of the fusible alloy is now to be poured upon a piece of board and worked up into a stiff paste by means of a flat piece of wood an operation that only occupies a few moments. The instant the alloy MOULDS FBOM FUSIBLE METAL. 1 09 has assumed the pasty condition the coin, being held by its gutta- percha handle, is to be promptly and firmly pressed upon the mass until it is sufficiently imbedded in it. In the course of a minute or so the coin may be withdrawn, when the mould should present a perfect and delicate impression of the original of course in reverse. Should any faults be visible, owing to want of dexterity on the part of the operator, the metal must be re-melted and the operation con- ducted again. A very little practice will enable the student to pro- duce moulds in this alloy with perfect ease. The coin, in each of the above cases, should be perfectly cold before applying it to the alloy. Large medals are moulded by simply dropping them a little side- waysinto the metal when on the point of solidification. Connecting the Mould to the Wire. "Wlien a perfect mould is obtained the conducting wire is to be attached, which is done by first scraping the longer end of the wire so as to render it perfectly clean ; it is then to be held in the flame of a candle, but at a little distance from the clean end. The mould being now held in the left hand, is to be brought near, but not touching, the flame, and, when the wire is sufficiently hot, it is to be pressed against the lack of the mould, when it will at once become imbedded in it, and in a few moments will be firmly set. A small portion of powdered resin applied to the spot will assist the union of the two metals. The back and upper edge of the mould must now be coated with sealing-wax varnish or some other quick-drying varnish, or, if carefully applied, paraffin wax (which melts at a very low heat) may be applied by first gently heating the mould and touching it with a small stick of the paraffin wax. It is well, also, to varnish that portion of the conduct- ing wire above the joint which has to be immersed in the copper bath, in order to prevent it from receiving the copper deposit. CHAPTER IX. ELECTRO-DEPOSITION OF COPPER (continued). Electrotyping by Separate Battery. Arrangement of the Battery. Copying Plaster Busts. Guiding Wires. Moulding in Plaster of Paris. Copy- ing Animal Substances. Electro-coppering Flowers, Insects, &c. Copy- ing Vegetable Substances. Depositing Copper upon Glass, Porcelain, &c. Coppering Cloth. Electrotyping by Separate Battery. In employing the single- cell apparatus, we have seen that it is necessary to keep up the strength of the solution by a constant supply of crystals of sulphate of copper, otherwise the solution would soon, become exhausted of its metal, and therefore useless. If we employ a separate battery, however, this method of sustaining the normal condition of the bath is unneces- sary, as we will now endeavour to show ; but in doing so we must direct the reader's attention for the moment to the principles of electrolysis, explained in a former chapter. The practical application of those principles may be readily expressed in a few words : If, in- stead of making the mould, or object to be copied, the negative element, as in the single-cell apparatus, we take a separate battery composed of two elements say, zinc and copper, as in Daniell's battery, we must then employ a separate copper solution or electrolytic bath, in which case the object to be deposited upon must be connected to the zinc element, as before, but the wire attached to the negative element of the battery (the free end of which is the positive electrode] must have attached to it a plate of sheet copper, which with the mould must be immersed in the solution of sulphate of copper. By this arrangement, while the copper is being deposited upon the mould, the sheet copper becomes dissolved by the sulphuric acid set free, forming sulphate of copper, which continued action re -supplies the bath with metal in the proportion (all things being equal) in which it is exhausted by deposi- tion of copper upon the mould. Arrangement of the Battery. At Eig. 56 is shown a Daniell's battery, A, connected, by its negative conducting wire (proceeding from the zinc), to the mould, B, with its face turned towards the copper plate or anode, c. The depositing vessel, D, which may be of AEBANGEMENT OF THE BATTERY. Ill glass or stoneware, for small operations, is'charged with an acid solu- tion of sulphate of copper, which is composed as follows : Sulphate of Copper i lb. Sulphuric Acid i Water (about) i gallon. The sulphate of copper, as before, is dissolved in a sufficient quantity of hot water, after which cold water is added to make up one gallon ; the sul- phuric acid is then added and the so- lution is set aside until quite cold, when it is to he poured into the depositing bath, which should be quite clean. When first placing the mould to be copied in the bath, a small surface only of the copper plate should be immersed in the solution, and this Fig. 56. may be gradually increased (by lowering the copper plate) as the deposit extends over the surface of the mould. In Fig. 54 is shown an arrangement in which several moulds are suspended by a brass rod laid across the bath B, the rod being con- nected to the zinc element of the battery, A, by the wire, x. Strips of sheet copper are suspended by a brass rod, c, which is connected by a binding-screw to the positive conducting wire, z, of the battery, which Fig- 57- in the woodcut represents a Daniell cell. In this arrangement, the sheet copper, by becoming dissolved in the solution during the electro- lytic action, keeps up the normal strength of the bath, which in the single -cell arrangement is attained by the supply of crystals of sulphate of copper. It may be well to mention that it is always preferable, besides being more economical of time, to deposit upon 112 ELECTRO-DEPOSITION OF COPPER. several moulds at a time in the bath, and this can be effected even with apparatus of small dimensions. The more extensive arrangements for depositing upon large objects by means of powerful battery currents will be considered in another chapter. Copying Flaster Busts. For this purpose, the elastic moulding material is used. Suppose we desire to obtain an electrotype from a small plaster bust, the object must first be well brushed over with boiled linseed. oil, and then set aside for two or three days to allow the surface to harden. In applying the oil, care should be taken not to allow it to touch the lower surface surrounding the orifice at its base, over which a piece of stout paper must be pasted to prevent the elastic material from entering the cavity, but before doing this partly fill the cavity with sand, to increase its weight. The bust is next to be suspended, upside down, by means of twine or thin copper wire, inside a jar sufficiently wide and deep to leave at least half an inch all round and at the bottom. When thus placed in its proper position, the elastic composition (page 97), having been previously melted, is poured in, and if any air-bubbles appear, these must be removed with the feather of a quill, when the vessel is allowed to rest until the composition is quite cold. The vessel is now to be inverted, when the solidified mass and the imbedded bust will gradually slip out. To facilitate this by prevent- ing the composition from sticking to the jar, it is a good plan to slightly oil the interior of the vessel in the first instance. Having removed the mould, it must now be separated from the plaster bust. This is done as follows : First place the mould in an erect position, base downward, then, with a thin knife, make an incision from the top to the base of the mould, at the back of the bust. The mould may now be readily opened where the incision has been made, and while being held open, an assistant should be at hand to gently remove the bust, when the mould, owing to its elasticity, will readily close itself again. It must next be secured in its proper position by being care- fully bound round with a bandage of tape. The mould is then to be inverted, and returned to the jar. A sufficient quantity of wax is now to be melted at the lowest temperature that will liquefy it, other- wise it will injure the mould ; it is then to be poured into the mould and allowed to rest until thoroughly cold. When cold, the elastic mould is to be again removed from the jar, and separated by untying the bandages from the wax-casting. This latter must now be well plumbagoed, a conducting wire attached, and the joint coated with plumbago as before directed. Since it will be difficult, however, to obtain an uniform deposit over such a comparatively large surface, it will be necessary to apply guiding wires, as they are called, and to which we must now direct special attention. COPYING PLASTER BUSTS. 113 Guiding Wires. The application of additional wires, to facilitate the deposition of copper in the cavities, or undercut surfaces, of moulds was first introduced by Dr. Leeson. A sufficient number of lengths of fine brass wire are twisted firmly round the main conduct- ing wire, at a short distance from its junction with the mould, and these, one by one, are bent in such a way that their extreme points may rest, lightly, upon the hollow surfaces of the mould, whereby the current is diverted, to a certain extent, from the main Fig. 58. wire to the cavities or hollows, which are less favourably situated for receiving the metallic deposit than the plane surfaces. The applica- tion of guiding wires is more especially necessary when the object to be copied is of considerable dimensions ; the principle of their arrangement is shown in Fig. 58. The mould, prepared as described, is to be put in connection with 114 ELECTRO-DEPOSITION OF COPPEE. the battery, by suspending it from the negative conducting-rod, and then gently lowered into the coppering bath. In the present case only a moderately stout deposit, or " shell," of copper will be necessary, since, as we shall explain, this deposit will, in the next operation, act the part of a mould, in producing a fac- simile of the original. When a perfect coating is obtained, of sufficient thickness to bear handling, it is to be removed from the bath, rinsed, and allowed to drain. It must then be heated sufficiently to melt the wax, which is allowed to run into any convenient receptacle, and the interior of the electrotype (which now represents a mould) must be cleansed from all adhering wax, by continuing the heat until the last drop ceases to flow. It must then be treated with spirit of turpentine, with the application of moderate heat, to dissolve out the remaining wax, the operation being repeated so as to entirely remove all traces of the wax. The next operation consists in depositing copper upon the interior of the copper mould, which may be readily done in the following way : A small quantity of sweet oil is first to be poured into the mould, which must be moved about so that the oil may spread all over the sur- face ; it must then be tilted over a vessel to allow the oil to run out, and next placed upon several folds of blotting-paper before a fire, for several hours, until the oil ceases to flow. The mould must now be carefully examined, and if any "pin-holes," as they are called, are visible, these must be stopped by melted wax dropped upon each spot upon the outside of the mould. The mould is now to be placed in a jar, in an inverted position, and held in its place by a padding of paper or rag, wedged around its base. The negative electrode (or wire connected to the zinc of the battery) is now to be connected to the mould, which may conveniently be done by soldering. A strip of stout sheet copper, attached to the positive electrode, is then to be suspended in the cavity of the copper mould, but not allowed to touch any part of it, and in this position it must be fixed securely, which may be conveniently done by a piece of wood laid across the orifice of the mould. The mould is now to be filled with the copper solution last mentioned, and the battery is then to be set in action. In order to obtain a good solid electrotype from the copper mould, it will be necessary to renew the copper plate, or anode, from time to time when it becomes worn away, unless it be of sufficient thickness to render such renewal unnecessary. The strength of the battery must also be well kept up by renewing the acid solution in the porous cell. When a deposit of sufficient thickness is obtained, the conducting wires may be disconnected, the copper solution poured out, and the interior rinsed with water. The next operation is to remove the shell of copper constituting the mould, which is done by breaking it away beginning at the base MOULDING IN PLASTEB OF PAKIS. 115 with a pair of pliers. When the first layer of metal has been lifted from the underlying deposit, the remainder may generally be peeled off with but little trouble, when the electrotype proper will be exhibited, and if successfully accomplished it will amply reward the operator for the trouble and care devoted to its production. The student should not, however, undertake the manipulation of the elastic moulding composition until he has acquired a skilful aptness in the simpler processes of electrotyping. It may be well to mention that the elastic composition may be re-used several times, provided it has been kept in a covered vessel, to exclude it from the action of either a moist or a very dry atmosphere. Moulding in Plaster of Paris. This material, especially for copying natural objects, such as leaves, ferns, fishes, &c., is exceed- ingly useful, and we will, as in former instances, first give the more simple method of applying it, so that the student may have no diffi- culty in its manipulation. To obtain a plaster mould from a coin or medal, for example, first oil the face of the object slightly by applying a single drop of oil, with a tuft of cotton wool, and with a fresh piece of wool gently rub the coin all over, so as to leave but a trace of oil on the surface, the most trifling quantity being sufficient to prevent the adhesion of the plaster to the original. A rim of card is now to be fixed round the medal, to form a receptacle for the plaster. A little cold water is then to be poured in a cup, or other convenient vessel, and a small portion of. fine plaster dropped into the water. The excess of water is now to be poured off and the plaster briskly stirred with a spoon. Now fill the spoon with the plaster (which should be about the consistency of cream) and pour it carefully over the face of the medal. If any air-bubbles appear, disperse them with a feather or camel-hair brush, which should be immediately after plunged into cold water, so that the plaster may easily be removed, and the brush thus left ready for future use. In about half -an-hour or so, the coin and mould may be detached, and the latter should then be placed in a moderately warm oven until dry. When perfectly dry, the face of the mould is to be well painted over with boiled linseed oil, repeating the operation several times ; or the mould may be saturated with wax, by pouring a little of this substance, in a melted state, over the face of the mould, and then placing it in the oven until the wax becomes absorbed by the plaster. When cold, the mould must be plumbagoed in the ordinary way, and a copper conducting wire attached by twisting the wire round its circumference, and forming a connection with the plumba- goed surface by means of a drop of melted wax, afterwards brushed over with plumbago. That portion of the wire which surrounds the mould should be coated with varnish to prevent the copper from being deposited upon it. The superfluous plumbago should, as in the Il6 ELECTRO-DEPOSITION OP COPPER. former cases, be removed, by scraping it away with a knife, leaving the connection, of course, untouched. The mould is now ready for the depositing bath, into which it must be gently lowered, so as to avoid breaking the connection between the conducting wire and the plumbagoed surface, a precaution which must in all similar cases be strictly observed. Copying Animal Substances. Suppose we desire to obtain an electrotype of a small fish (the scaly roach being very suitable), for example. The object is first brushed over lightly with a little linseed oil ; we next mix a sufficient quantity of plaster of Paris into a thinnish paste, and pour this in a shallow rim of metal or stout cardboard placed upon a piece of glass or sheet of paper, previously rubbed over with a little oil or grease ; before the plaster has time to set, the fish is to be held by its head and tail, and laid on its side upon the paste, using sufficient pressure to imbed one half of the fish. To assist this, the soft plaster may be worked up or guided to its proper places by means of a knife-blade, care being taken to avoid spreading the plaster beyond that part which is to form the first half of the mould. The plaster is now allowed to set hard, which occupies about half an hour. We next proceed to mould the second half of the fish. A small brush, say a painter's sash tool, is dipped in warm water, and then well rubbed over a lump of soap ; this is to be brushed all over the plaster, but avoiding the fish, and the soap and water applied several times to ensure a perfect coating. A rim of greater depth, say f of an inch deeper, must be fixed round the mould, in place of the former rim, and a second quantity of plaster made into a thinnish paste, as before, which must then be carefully poured over the fish and upper surface of the mould, taking care not to let it flow over the rim. This second batch of plaster should be sufficient to form a thick half mould, as in the former case, otherwise it may break when being separated from the first half mould. When the plaster has set quite hard, the two moulds may be sepa- rated by gently forcing them asunder, the soap and water having the effect of preventing the two plaster surfaces from adhering, while the oil applied to the fish also prevents the moulding material from sticking to it. When the two halves of the mould are separated, the fish is to be carefully removed, and the plaster moulds placed in a warm, but not very hot, oven, and allowed to become perfectly dry. They are then to be placed faced downwards in a plate or other shallow vessel, containing melted bees -wax, and allowed to remain until saturated with the material, especially on the faces of the moulds ; these are now allowed to become quite cold, when they are ready to receive a coating of plumbago, which must be well brushed into every part of the impression, until the entire surfaces present the bright COPYING ANIMAL SUBSTANCES. 117 metallic lustre of a well -polished fire-stove. The conducting wire must now be attached, which may be effected in this way : Bend a piece of stout copper wire in the form shown in Fig. 59, and pass the mould under the hook at a, and beneath the coil of the wire at b ; the shorter end of wire at a should just touch the edge of the im- pression, near the mouth or tail of the fish. The wire thus adjusted must be secured firmly in its place, by being bound to the mould with thin copper wire. Before placing the conducting wire in its position, as above described, it will be advisable to wipe away all superfluous plumbago from the face of the mould, carefully avoiding injury to the impression, and when the conducting wire is adjusted, it is a good plan to coat the wire at all parts but the extreme point at a with varnish, or melted paraffin wax, to prevent the copper from becoming deposited upon it. The end of the wire at a must be put in metallic contact, so to speak, with the plum- bagoed impression, by brushing a little of that substance over the point of junction. Thus prepared, the long end of the conducting wire is to be connected to the negative pole of the battery, and the mould gently immersed in the bath, the copper anode previously being suspended from the positive electrode. The second half mould may now be treated in same way j as the above, and when two perfect electrotypes, or shells, are obtained, the superfluous copper should be removed by aid of a pair of pliers and a file ; when this is done the inner edges of each electrotype may be tinned, by first brushing a little chloride of zinc round the edge, and then passing a soldering iron, charged with pewter solder, over the surface. When the two halves of the fish are thus all prepared, they may be brought together and held in posi- v^ tion by means of thin iron " binding wire." The flame of Fig. 59. a spirit-lamp or a blow-pipe flame may now be applied, which, by melting the solder, will soon complete the union, when a perfect representation of a fish will be obtained. This may after- wards be bronzed, gilt, or silvered by the processes described here- after, and, if desired, mounted upon a suitable stand. The elastic moulding material may also be used for copying animal substances ; in this case, one half of the fish must be imbedded in moulding sand ; a cylinder of thin sheet tin, bound together with fine copper wire, or by soldering, is then placed round the sand, so as to enclose it, and the sand is made as level as possible, by gently pressing it with any convenient instrument. The melted elastic material is now to be poured into the cylinder, which should be about two inches higher than the highest part of the object, until it nearly Il8 ELECTRO-DEPOSITION OP COPPEE. reaches the top ; it is then allowed to rest for at least twelve hours, when the metal rim is to be removed and the mould withdrawn ; the object is next to be liberated from the mould, and the other half moulded in the same way. The wax and stearine composition is to be poured into each half mould, and from the models thus ob- tained plaster moulds may be procured in the same way as from the natural object, but in this case the wax models must be well brushed over with plumbago before being- embedded in the plaster. Since electrotypes of fishes look exceedingly well as wall ornaments, it will be only necessary, for this purpose, to obtain an electrotype of one half of the fish, which may, after trimming and bronzing, be cemented to an oval board, stained black and polished, and, if desired, mounted in a suitable frame. Electro-Coppering Flowers, Insects, &c. Fragile objects, to which the ordinary methods of plumbagoing could not be applied, may be prepared to receive a deposit of copper in the sul- phate bath by either of the following methods : i. The object, say a rose-bud or a beetle, for instance, is first attached to a copper wire ; it is next dipped in a weak solution of nitrate of silver (about forty grains of the nitrate dissolved in one ounce of distilled water), and after being allowed to drain, but before it is dry, it is to be ex- posed to the vapour of phosphorus under a bell-glass. To produce the vapour a small piece of phosphorus is dissolved in a little alcohol ; this is poured into a watch-glass (chemi- cal "watch-glasses" are readily procurable), which is then placed in a plate containing hot sand. The object being (5 fixed by its wire in such a position that it cannot shift, the Fig. 60. bell-glass (an ordinary fern-glass will answer admirably) is to be placed over the whole, and allowed to remain undis- turbed for about half an hour. The sand should not be hot enough to endanger the bell-glass. By this process, the silver of the nitrate^ is reduced to its metallic state, causing the object to become a conductor of electricity ; it is then ready for the coppering bath, in which it must be immersed with great care. Since very light objects will not sink in the solution bath, it is a good plan to form a loop in the conducting wire, as shown in Fig. 60, to which a piece of strong silk thread or twine, having a small leaden weight connected to the opposite end, may be fastened, as in the sketch. By this simple contrivance light objects andjloatififf moulds, as those made of gutta- percha, wax, &c., may be easily sunk into the bath, and retained therein until sufficiently coated. 2. The most effective application of phosphorus for the above pur- pose consists in dipping the object in a solution of phosphorus in ELECTRO-COPPERING FLOWERS, ETC. IJQ bisulphide of carbon. This highly volatile and inflammable substance dissolves phosphorus very freely; the solution, known as "Greek fire," is a most dangerous compound to handle, and if any of it drop upon the skin it may produce sores of a serious nature ; more- over, if it be incautiously allowed to drop upon the clothing, or upon the floor, it may afterwards ignite and do much mischief. In employ- ing the solution of phosphorus, therefore, the greatest possible care must be observed. The object, being attached to a wire, is dipped into the solution, and after being allowed to rest for a few seconds, is next immersed in a weak solution of nitrate of silver, and afterwards allowed to dry in the light. If the object, after being dipped in the phosphorus solution, be allowed to remain in the air for more than a few seconds before being placed in the nitrate solution, it is very liable to become ignited. The solution of phosphorus is prepared by dissolving a small portion of the substance in bisulphide of carbon, about one-twentieth part of the former being sufficient for the purpose. 3. A safer method of producing a conducting surface on these objects is to employ an alcoholic solution of nitrate of silver, made by adding an excess of powdered nitrate of silver to alcohol, and heating the mixture over a hot -water bath. The object is to be dipped in the warm solution for an instant, and then exposed to the air for a short time until the spirit has evaporated. If now submitted to the fumes of phosphorus, as before described, the film of nitrate of silver soon becomes reduced to the metallic state, when the object is ready for the coppering bath. To render non-metallic substances conductive, Mr. Alexander Parkes introduced the subjoined ingenious processes. i. A mixture is made from the following ingredients : Wax or tallow i ounce India-rubber i drachm Asphalte i ounce Spirit of turpentine . . . . . . ij fl. ounce The india -rubber and asphalte are to be dissolved in the turpentine, the wax is then to be melted, and the former added to it and in- corporated by stirring. To this is added one ounce of a solution of phosphorus in bisulphide of carbon, in the proportion of one part of the former to fifteen parts of the latter. The articles, being attached to a wire, are dipped in this mixture ; they are next dipped in a weak solu- tion of nitrate of silver, and when the black appearance of the silver is fully developed, the article is washed in water ; it is afterwards dipped in a weak solution of chloride of gold, and again washed. Being now coated with a film of gold, it is ready for immersion in the copper bath. I2O . ELECTRO-DEPOSITION OF COPPEE. 2. In this process, the solution of phosphorus is introduced into the materials used for making the mould, thus : Wax and deer's fat, of each pound Melt together and then add : Phosphorus TO grains Dissolved in bisulphide of carbon . . . 150 The wax mixture must be allowed to become nearly cool, when the phosphorus solution is to be added very carefully, through a tube dipping under the surface of the mixture ; the whole 'are then to be well incorporated by stirring. Moulds prepared from this composition, are rendered conductive by being first dipped in a solution of nitrate of silver, then rinsed, and afterwards dipped in a weak solution of chloride of gold, and again washed, when they are ready for the coppering solution. Copying Vegetable Substances. The leaves of plants, seaweeds, ferns, &c., may be reproduced in electrotype, and form very pleasing 1 objects of ornament when successfully produced. If we wish to copy a vine-leaf, for example, the leaf should be laid face down- wards upon a level surface, and its back then covered with several layers of thin plaster of Paris until a tolerably stout coating is given ; the leaf is then to be inverted and embedded in a paste of plaster, care being taken not to allow the material to spread over the face of the leaf. When the plaster has become hard, finely powdered plum- bago is to be dusted over the entire surface from a muslin bag. A rim of pasteboard, slightly greased on one side, is now to be fixed round the outer edge of the plaster, and secured by a piece of twine. To render this more easy, the plaster may be pared away with a knife, so as to leave a broad flat edge for the card rim to rest against. Melted wax is now to be poured into the pasteboard cylinder thus formed, in sufficient quantity to make a tolerably stout mould. When thoroughly cold, the rim is to be removed and the mould liberated carefully. It is then to be plumbagoed, connected to the negative electrode of the battery, and immersed in the copper bath. The elastic material may also be employed in making moulds from vege- table objects. Depositing Copper upon Glass, Porcelain, &c. The article should first be brushed over with a tough varnish, such as copal, or with a solution of gutta-percha in benzol; when dry it is to be well plumbagoed. In some cases it may be necessary to render the surface of the glass rough, which is effected by submitting it to the fumes of hydrofluoric acid ; this is only necessary, however, when the vessel is of such a form that the deposited copper might slip away DEPOSITING COPPER UPON GLASS, ETC. 121 from the glass. Porcelain capsules, or evaporating dishes, may receive a coating of copper at the outside, by varnishing this surface, extend- ing the coating to the upper rim of the vessel, then applying the plumbago and depositing a coating of copper of sufficient thickness. Grore says, " The only effectual way of obtaining an adhesive deposit upon glass or porcelain is -to send the article to a glass or porcelain gilder, and have gold burnt into its surface, and then depositing upan the gold coating in the usual manner." MM. Noualhier and Prevost patented a process for producing a conducting surface upon glass or vitreous substances, which consists in first coating the object with var- nish or gold size, and then covering it with leaf copper. By another method they triturated bronze powder with mercury and common salt, and then dissolved out the salt with hot water, leaving the bronze powder to settle. When dry, this powder is to be applied to the varnished object in the same way as plumbago. For this purpose, however, Bessemer bronzes, which are exquisitely impalpable, and produce a very good conducting surface, may be employed with or without being mixed with plumbago. Coppering Cloth. In 1843, Mr. J. Schottlaender obtained a patent for depositing either plain or figured copper upon felted fabrics. The cloth is passed under either a plain or engraved copper roller, immersed horizontally in a sulphate of copper bath, containing but little free acid. The deposit takes place upon the roller as it slowly revolves ; the meshes of the cloth are thus filled with metal, and the design of the roller copied upon it. The coppered cloth is slowly rolled off and passes through a second vessel filled with clean water. The roller is previously prepared for a non-adhesive deposit. CHAPTER X. ELECTRO-DEPOSITION OF COPPER (continued}. Electrotyping Printers' Set-up Type. Plumbagoing the Forme. Prepara- tion of the Mould. Filling the Case. Taking the Impression. The Cloth. Removing the Forme. Building. Plumbagoing 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. Electrotyping Wood Engravings, &c. Tin Powder for Electrotyping. OF all the purposes to which the art of electrotyping is applied, none is of greater importance than its application to letterpress print- ing and the copying of wood engravings to be printed from instead of from the wooden blocks themselves. Although this latter branch of the art is very extensively adopted in this country, in the reproduction of large and small engraved blocks for illustrated works and periodicals, newspaper titles, c., the application of electrotyping as a substitute for stereotyping in letterpress printing has not, as yet, attained the dignity of an art in England. In America, however, the art of re- producing set-up type in electrotype copper has not only acquired a high state of development as a thoroughly practical branch of electro - deposition, but it has almost entirely superseded the process of stereo- typing. There are several reasons why this art has been more fully developed in the States than here. In the first place our transatlantic kindred are more prompt in recognising and adopting real improve- ments ; they are less mindful of cost for machinery when the object to be attained is an important one ; they are not so much tinder the influence of so-called "practical men" as to ignore scientific help ; finally, they do not wait until all their competitors have adopted a process before they run the risk of trying it for themselves. During the past few years we have been much, impressed by the extreme beauty of the American printing, and the exquisite brilliancy of their engravings. Being printed from copper surfaces, the ink delivers more freely than from stereotype metal, while, we believe, a smaller amount of ink is required. Again, the Americans extensively employ wood pulp in the manufacture of their paper, and this material being less absorbant than cotton-pulp, causes the ink to remain on the ELECTROTYPING PRINTERS SET-UP TYPE. 1 23 surface rather than to sink into the substance of the paper a fact which was established by the author's father, the late Mr. Charles Watt (the inventor of the wood-paper process), when it was first exhibited in London in the year 1853,* in the presence of the present Earl of Derby and many scientific men and representatives of the press. With a full belief that the American system of electrotyping, as applied to letterpress printing, will eventually be adopted in this country at first by the more enterprising members of the printing community we propose to explain as concisely as the subject will admit the method which has been practically adopted in the United States, and we have to thank the distinguished firm of R. Hoe and Co., of New York, the well-known manufacturers of printing and electrotyping machinery, for much of the information we desire to convey, as also for their courtesy in furnishing us, at our request, with electrotypes of their machinery for the purposes of illustration. We are also indebted to Mr. Wahl f for additional information on this subject. "As applied to letterpress printing, electrotyping is strictly an American art." This is the claim put forward by the firm referred to, and we freely acknowledge the fact. We gave our cousins the art of electrotyping, and in exchange they show us how we may apply it to one of the most useful of all purposes the production of good printing from a more durable metal than either ordinary type or stereotype metal. Electrotyping Printers' Set-up Type. In pursuing the art of electrotyping, as applied to letterpress printing, the compositor, electro- typer, and mounter must work with one common object, each having a knowledge of what the other requires to perform his part of the work properly. In carrying out the operation on an extensive scale, the depositing room should be on the ground floor, owing to the weight of the vats, and the flooring should be cemented and well drained. The apartment should be well lighted, and provided with an ample supply of water. The depositing vats may be of wood, lined with pitch ; and where a magneto or dynamo -electric machine is employed, this should be fixed at such a distance from the vats as not to be in the way, but at the same time to be as near to them as possible with- out inconvenience. * Manufacturers in this country refused to adopt this process. It was, however, " taken up " in America in the same year, where it has been worked ever since. It is now used in this country to some extent, as also in many other parts of the world. t " Galvanoplastic Manipulations." By W. H. Wahl. 124 ELECTRO-DEPOSITION OP COPPER. Preparing the Formes. "When the formes, or pages of set-up type, have to be electrotyped, it is necessary that great care should be exercised in selecting the types, rules, &c., in. justifying the same, and in locking-up the forme. When the art of electrotyping comes to be a recognised substitute for stereotyping, it is probable that some modi- fications in the structure of printers' type may be made to suit more fully the requirements of the electro typer than the ordinary type. The following suggestions are given relative to the composition of the type for reproduction in electrotype, and these should be well under- stood by those who may hereafter be called upon to produce electro- types from printers' formes. Composition. Every quadrat, space, lead-slug, reglet, or piece of fur- niture should be high. Some leads have one or both edges bevelled ; but even though the bevel is small it is sufficient to cause considerable trouble, and such leads should not be used in moulding, as the wax is sure to be forced into the space of the bevel, to be broken off, and to require extra labour in distributing the type, besides making it neces- sary to scrape the wax from the leads before they can be used again. So far as possible, use thick rules and those having a bevel on each side of the face. Thin rules make so small an opening in the wax that there is great difficulty in blackleading the mould, and in the bath the copper may bridge across a small opening, leaving the face and sides of the rule uncovered, or at most with but a thin, imperfect deposit that is useless. For this reason, type having considerable bevel, is best for electrotyping. English type has more bevel than American. Bevelled rules also make impressions in which the hairs of the blackleading brush can penetrate more deeply. Type-high bearers, or guards, about of an inch thick, should be put around each page, and scattered through blank spaces, to prevent the wax from spreading while the forme is pressed in it, and also to facilitate the operation of "backing." If there are several pages in a forme, separate them by two guards ; one guard does not give sufficient room to saw between the pages and leave enough of the bearer to protect the edges of the plate in " shaving." "When the matter occupies but a portion of a page, or the lines are shorter than the full width of the page, as in poetry, an em dash or a letter should be placed bottom up in each corner of the page, as a guide to the finisher in trimming the the plate. "When the folio is at one corner, that will answer for one of the guides. All large blanks, chapter heads, and lines unprotected by other matter, should have type -high bearers so placed as to guard the exposed parts from injury. Locking-up. The formes must be locked much tighter than for printing, for, in order that the mould shall be perfect, the wax must enter and fill solidly all the interstices of the forme. This requires ELECTROTYPING- PRINTERS SET-UP TYIE. 125 great pressure, and the movement of the wax caused by the entering of the type in taking the impression, or mould, is very likely to dis- place any portions of the forme that may be loose. A proof should always be taken after the forme is locked up for the foundry, and both should be examined to make sure that no part has shifted in driving the quoins. Sometimes the matter is set with high spaces but low leads, or vice versa, or low spaces but no leads ; frequently copper- faced and white-faced type are used in the same forme. None of these combinations should be allowed, but the whole forme should be either high spaces and high leads or low spaces and low leads. In offices having no high quads, &c., low material must be used; but greater care is necessary in preparing the forme, more labour required of the electrotyper, and the plate is much less satisfactory than when high material is used. Woodcuts which are locked up with the type must be perfectly cleaned with naphtha or benzine, and dried thoroughly before the forme is blackleaded, and great care must be taken not to clog the fine lines of the engraving. Moulds should not be taken from electrotype cuts, since much better ones can be obtained direct from the woodcut. Correcting the Matter. When necessary to make alterations in electrotype plates, the matter for corrections should be setup and elec- trotyped, but the compositor should separate each correction by a space about a pica, in order that there may be room to saw between them. If the alteration is but a single letter or short word, it is usual to solder the type to the plate. By setting up corrections in their regular order, the labour and cost of plate alterations may frequently be much reduced. The above technical hints will aid the electrotyper into whose hands a printers' forme may be placed for reproduction in electrotype copper. Plumb agoing the Forme. The forme of type must first be cleansed from printing-ink, if very dirty, either with potash ley or benzine ; or, if not very dirty, with water distributed from a rubber pipe with rose sprinkler, after which it must be dried. The forme is next to be well brushed over with plumbago, to prevent the wax from sticking. This is applied with a soft hand-brush, the plumbago being made to penetrate every crevice. In doing this, great care must be taken not to fill up the fine lines of the forme with the plumbago. Preparation of the Mould. For this purpose a moulding case (Fig. 61) is employed, which is a flat brass pan about three -sixteenths of an inch in depth, with two flanges, which fit into the clamps of the moulding press. This is fitted with an " electric connection gripper." The moulding composition consists of the best pure yellow beeswax, to 126 ELECTEO-DEPOSITION OF COPPEK. which is added from five to twenty per cent, of virgin turpentine, to prevent it from cracking. If the temperature of the apartment is from 90 to 95 Fahr., the wax may not require any addition. The composition should be melted by steam heat.* Filling the Case. The moulding case having been slightly warmed, on the steam- heating table, a, Fig. 62, is placed on the case-filling table, b, truly levelled, and the melted wax, contained in the small jacketed pan, is poured into it with a clean iron or copper ladle, great care being taken to run the wax entirely over the case while it is hot, so that it may not, by cooling too quickly in any part, cause irregularities Fig. 6x.-Mwell plumbagoed, after which the con- necting wire and " guiding wires " are attached ; it is then ready for the depositing bath, where it is allowed to remain until a shell of sufficient thickness is obtained, which will depend upon the size of the mould and the strength of the current employed. Under favour- able conditions, a shell of copper, say, of about one square foot of surface, will be obtained in about eight or ten hours, or even less ; it is commonly the practice to put a series of moulds in the bath towards the evening, and to leave them in the bath all night ; on the following morning the deposit is found to be ready to separate from the mould. In electrotype works where magneto or dynamo machines are em- I>loyed (as in some of our larger printing establishments), a good shell is obtained in from three to five hours,* according to the dimensions of the mould. After removing the mould from the bath, it is rinsed in water, and the shell carefully detached, and the electrotype is next backed-up with solder or a mixture of type metal and tin, the back of the electrotype being first brushed over with a solution of chloride of zinc. The edges of the electrotype are next trimmed with a circular saw, and are afterwards submitted to the planing machine, by which the backing metal is planed perfectly level and flat ; the edges are then bevelled by a bevelling machine, when the plate is ready for mounting on a block of cedar or mahogany, which is effected by * An American electrotypist, on a visit to London, told the author, about five years ago, that, having adopted the Weston dynamo machine in place of voltaic batteries, he could deposit a shell of copper upon fifteen moulds, each having about two square feet of surface, in about two and a half hours ; that is to say, by the time the fifteenth or last mould was put into the bath the one which had first been immersed was sufficiently coated for backing up. 138 ELECTRO-DEPOSITION OF COPPER. means of small iron pins driven into the bevel edges of the backing- metal. When complete, the block, with its mounted electrotype, should be exactly type high. Respecting electrotypes from wood engravings, or " electros," as they are commonly called in the print- ing trade, we may mention that many of our larger illustrations are produced from electrotypes. Engraved steel plates are copied in the same way as above, and their reproduction in copper by the elec- trotype process is extensively practised. Tin Powder for Electrotyping. Grain tin may be reduced to an impalpable powder by either of the following methods : I. Melt the gram tin in an iron crucible or ladle, and pour it into an earthenware mortar, heated a little above its melting point, and triturate briskly as the metal cools. Put the product in a muslin sieve and sift out the finer particles, and repeat the trituration with the coarser par- ticles retained in the sieve. To obtain a still finer product place the fine powder in a vessel of clean water and stir briskly ; after a few seconds' repose, pour off the liquor in which the finer particles are suspended, and allow them to subside, when the water is to be again poured off and a fresh quantity of the powder treated as before. The impalpable powder is finally to be drained and dried, and should be kept in a wide -mouthed stoppered bottle for use. 2. Melt grain tin in a graphite crucible, and when in the act of cooling, stir with a clean rod of iron until the metal is reduced to a powder. The powder should then either be passed through a fine sieve or elutriated as above described, which is by far the best method of obtaining an absolutely impalpable product. In using this powder for electro typing pur- poses in the manner previously described, it must not be forgotten that the tin becomes dissolved in the copper bath ; it should therefore only be employed in a bath kept specially for the purpose, and not be suffered to enter the ordinary electrotyping vat. CHAPTER XI. ELECTRO-DEPOSITION OF COPPER (continued}. Deposition of Copper by Dynamo-electricity. Copying Statues, &c. Le- noir's Process. Deposition of Copper on Iron. Coppering Printing Rollers. Coppering Steel Wire for Telegraphic Purposes. Walenn's Process. Gulensohn's Process. Weil's Coppering Process. Electro- etching. Glyphography. Making Copper Moulds by Electrolysis. Making Electrotype Plates from Drawings. Deposition of Copper by Dynamo -electricity. Within the past few years, owing to the great advance made in the production of powerful and reliable magneto and dynamo -electric machines, the re- duction of copper by electrolysis in the various branches of electro - deposition has assumed proportions of great magnitude ; and while nickel -deposition which fifteen years ago was a comparatively un- developed art has quietly settled down into its legitimate position as an important addition to the great electrolytic industry, the electro - deposition of copper, and its extraction from crude metal, have pro- gressed with marvellous rapidity, both at home and abroad, but more especially so within the past three or four years, and we may safely predict from our knowledge of the vast number of magneto and dynamo machines which are now being constructed, under special contracts, that in a very short time the electrolytic reduction of copper will reach a scale of magnitude which will place it amongst the foremost of our scientific industries in many parts of the world. Before describing the processes of coppering large metallic objects, we must turn our attention to the production of electrotypes of larger dimensions than those previously considered. At a very early period of the electrotype art, Russia, under the guidance of the famous Professor Jacobi, produced colossal statues in electrolytic copper, which at the time created profound astonishment and admiration. About the same period our own countrymen directed their attention to this appli- cation of electrotypy, and at subsequent periods electrotypes of con- siderable dimensions were produced not only in this country but on the Continent. Some exceedingly fine specimens have been produced by Messrs. Elkington & Co., one of the most notable of which is I4O ELECTRO-DEPOSITION OF COPPEE. that of the Earl of Eglinton, 13 J feet high and weighing two tons, while some other equally good specimens of life-size busts and bas- reliefs are to be seen in "Wellington College, the House of Lords, &c. The well-known Paris firm, Messrs. Christofle & Co., have also produced colossal electrotype statues, one of which is 29 feet 6 inches in height, and weighs nearly three tons and a half ; the completion of the deposit occupied about ten weeks. Copying Statues, &c. "When very large objects have to be repro- duced in electrotype, the method adopted is usually as follows : The original, formed of plaster of Paris, produced by the modeller or sculptor, is first brushed all over with boiled linseed oil, until the sur- face is completely saturated with the drying oil. After standing for two or three days, according to the temperature and condition of the atmosphere, the object, which is thus rendered impervious to moisture, and readily receives a coating of plumbago, is thoroughly well brushed over with blacklead until the entire surface is perfectly coated with the conducting material. The model is next connected to conducting wires, assisted by guiding wires, and placed in a sulphate of copper bath, where it receives a deposit of about one -sixteenth of an inch in thick- ness, or a shell sufficiently stout to enable it to retain its form after the inner plaster figure has been removed, which is effected in this way : the electrotype, with its enclosed model, being taken out of the bath, is first thoroughly well rinsed, the copper shell is then cut through with a sharp tool at suitable places, according to the form of the original figure, by which these various parts, with their guiding wires attached, become separated ; the plaster figure is then carefully broken away, and all parts of it removed. After rinsing in hot water, the outer surface of the copper " formes " are well varnished over to prevent them from receiving the copper deposit in the next operation. The formes are next exposed to the fumes of sulphide of hydrogen, or dipped in a weak solution of sulphide of potassium (liver of sulphur), to prevent the adhesion of the copper deposit. These " formes," or parts of the electrotype shell, constitute the moulds upon which the final deposit, or electrotype proper, is to be formed, and these are re- turned to the depositing tank and filled with the solution of sulphate of copper, anodes of pure electrolytic copper being suspended in each portion. Deposition is then allowed to take place until the interior parts or moulds receive a coating of from one-eighth to one-third of an inch in thickness. The various pieces are then removed from the bath, and after well rinsing in water, the outer shell, or mould, is carefully stripped off, and the respective parts of the electrotype figure are afterwards fixed together when the operation is complete. Lenoir's Process. A very ingenious method of electrotyping large figures was devised by M. Lenoir, which consists in first taking im- COPPERING PRINTING ROLLERS. 14! pressions in gutta-percha of the object in several pieces, which may afterwards be put together to form a perfect figure ; the inner sur- faces of these impressions, or parts of the mould, are then well coated with plumbago. A "dummy" of the form of the interior of the mould, but of smaller dimensions, is now formed of platinum wire, to act as an anode, and the several parts of the plumbagoed gutta-percha mould are put together to form a complete mould all round it. The mould, with its platinum wire core (the anode) which is insulated from metallic contact with the mould by a covering of india-rubber thread is then placed vertically in the bath, weights being attached to allow the mould to sink into the solution. The platinum anode and the plumbagoed mould are then put in circuit and deposition allowed to progress. To keep up the strength of the copper solution within the mould, in the absence of a soluble anode, a continual flow of fresh copper solution is allowed to enter the mould, from a hole at the top of the head, which makes its escape through holes in the feet of the mould. When a sufficiently stout deposit is obtained, the flexible wire anode is withdrawn through the aperture in the head, after which the various portions of the gutta-percha mould are re- moved, and the seams at the junctions of the electrotype are cleared away by appropriate tools. Deposition of Copper on Iron. Since iron receives the copper deposit from acid solutions without the aid of a separate current, and the deposit under these conditions is non- adherent, it is the practice to give a preliminary coating of copper to iron objects in an alkaline bath, ordinary cyanide solutions being most generally adopted for this purpose. Many other solutions have, however, been recom- mended, some of which may deserve consideration. In any case, the iron article is first steeped in a hot potash bath, when the presence of greasy matter is suspected, and after rinsing, is immersed in a pickle of dilute sulphuric acid, ^ Ib. of acid to each gallon of water. After well rinsing, the article is scoured with coarse sand and water, applied with a hard brush, and after again rinsing, is immersed in the alkaline bath until perfectly coated with a film of copper. It is then again rinsed, and at once placed in a sulphate of copper bath, where it is allowed to remain until a sufficiently stout coating of copper is obtained. In some cases, where the object is of considerable propor- tions, it is kept in motion while in the solution, by various mechanical contrivances, as in "Wilde's process, to be referred to shortly. Coppering Printing Rollers. Many attempts have been made, during the past thirty years or so, to substitute for the costly solid copper rollers used in calico-printing, iron rollers coated with a layer of copper by electrolysis. The early efforts were conducted with the ordinary voltaic batteries, but the cost of the electricity thus obtained 142 ELECTRO-DEPOSITION OF COPPER. was far too great to admit of the process being practically successful, while at the same time the operation was exceedingly slow. A method which was partially successful consisted in depositing, in the form of a flat plate, an electrotype bearing the design, which was afterwards coiled up in a tubular form, and connected to an iron cylinder or roller by means of solder, the seam being afterwards touched up by the engraver. A far better system, however, is now adopted, which is in every way perfectly successful ; and printing rollers are produced in large quantities by electro -deposition at about one -half the cost of the solid copper article. Before describing the methods by which cast-iron rollers are faced with copper at the present time, it may be instructive to consider briefly some of the means that have been adopted to deposit a sufficient thickness of copper upon a cast-iron core to withstand the cutting action of the engraver's tools. Schlumberger's Process. This consists in depositing copper upon previously well-cleaned cast-iron cylinders by means of the " single- cell " process. The solution bath consists of a mixture of two solu- tions composed of (i) Sulphate of copper, I part; sulphate of soda, 2 parts ; carbonate of soda, 4 parts ; water, 16 parts. (2) Cyanide of potassium, 3 ; water, 12 parts. The interior of the bath is surrounded by porous cells containing amalgamated zinc bars with copper wires attached, and dilute sulphuric acid. The solution is worked at a temperature of from 59 to 65 Fahr., and the iron cylinder, being put in contact with the zinc elements, remains in the bath for twenty - four hours, at the expiration of which time it is removed, well washed, rubbed with pumice -powder, again washed in a solution of sulphate of copper having a specific gravity of I 161, containing ^jth part of its volume of sulphuric acid ; scraps of copper are kept in the bath, to sup- ply the loss of copper, and prevent the liquid becoming too acid. The cylinder is then returned to the bath, or placed in a mixture composed of the folio wing two solutions : (i) Acetate of copper, 2 ; sulphate of soda, 2 ; carbonate of soda, 4 ; water, 16 parts. (2) Cyanide of po- tassium, 3 ; liquid ammonia, 3 ; water, 10 [parts. The cylinders are to be turned round once a day, in order to render the deposit uniform, and the action is continued during three or four weeks, or until the deposit is - 2 \th of an inch thick. Another method consists in first coppering the well- cleaned cast- iron cylinder in an ordinary alkaline coppering bath, and then trans- ferring it to an acid bath of sulphate of copper, the cylinder in each case being surrounded by a hollow cylinder of copper for the anode ; the process is allowed to proceed slowly, in order to obtain a good reguline coating, and when this is obtained of sufficient thickness to bear engraving upon, the surface is rendered smooth by turning at the lathe. COPPERING PRINTING ROLLERS. 143 Producing Printing Boilers by magneto-electricity. Wilde's Process. It is obvious that the electrical power obtained from mag- neto and dynamo -electric machines is more capable of depositing econo- mically the requisite thickness of copper upon cast -iron cylinders to form printing rollers than could be expected from voltaic electricity, which necessarily involves the solution of an equivalent of zinc and the con- sumption of sulphuric acid to deposit a given weight of copper. It is well known that deposition takes place more freely upon the lower surfaces of the cathode, and consequently, when the deposited metal is of any considerable thickness, the irregular surface thus produced is often a source of great trouble to the electro -depositor ; in the case of printing rollers, however, in which a perfectly uniform thickness of the deposit is absolutely indispensable, some means must be adopted to render the deposit as uniform as possible from end to end of the cylinder. To accomplish this, Mr. Henry "Wilde, of Manchester, effected an arrangement for which he obtained a patent in 1875, which consists in ' ' giving to the electrolyte or depositing liquid in which the roller to be coated is immersed, or the [positive and nega- tive electrodes themselves, a rapid motion of rotation, in order that fresh particles of the electrolyte may be brought successively in con- tact with the metallic surfaces. By this, " says the patentee, "powerful currents of electricity may be brought to bear upon small surfaces of metal without detriment to the quality of the copper deposited, while the rate of the deposit is greatly accelerated. " Motion may be communicated to the electrolyte, either by the rotation of the electrodes themselves, or when the latter are stationary, by paddles revolving in an annular space between them. The iron roller to be coated with copper is mounted on an axis, the lower end of which is insulated, to prevent its receiving the deposit of copper at the same time as the roller. The roller, after having received a film deposit of copper from an alkaline solution in a manner well under- stood, is immersed in a vertical position in a sulphate solution of copper, and a motion of rotation is given to the roller or rollers by means of suitable gearing. The positive electrodes are copper rollers or cylinders, of about the same length and diameter as the roller to be coated, and are placed parallel with it in the sulphate solution. The electrical contacts are made near the upper and lower extremities of the electrodes respectively, for the purpose of securing uniformity in the thickness of the deposit. The sulphate solution may be main- tained at an uniform density, from the top to the bottom of the bath, by rotating a small screw propeller, enclosed in a tube communicating with the liquid, and driven by the same gearing that imparts motion to the roller." The electric current employed for depositing copper by the above 144 ELECTRO-DEPOSITION OF COPPER. method may be obtained from Wilde's magneto -electric machine, which has been very extensively adopted for this purpose, or from any dynamo electric machine capable of yielding- an adequate current. Mr. Wilde says, in the specification above quoted, " Although I have only mentioned cast-iron as the metal upon which the copper is deposited, the process is applicable to rollers made of zinc or other metals, and their alloys. The method of accelerating the rate of de- posit, by giving to the electrolyte, or to the electrodes, a motion of rotation, may.be applied to the electrolytic method of refining copper described in Mr. J. B. Elkington's patent." Mr. Wilde's system of coppering cast-iron rollers was established in 1878, but he subse- quently disposed of his patent rights to the Broughton Copper Company, who carry on the process successfully, and have extended it to the coating of hydraulic rams, &c. The coppering of cast-iron rollers is also carried on by the Electro - Metallurgical Company, London, by whom, also, electrotype rollers for impressing leather, &c., are produced, the machine employed being the Hallett-Elmore dynamo. Rollers which have been used, and the engraved design upon which is no longer required, are first submitted to a lathe, in which the design is removed by turning, and the rollers are then placed in the depositing vats until a sufficient coating is obtained, after which they are again prepared for engrav- ing. The arrangement consists of large tanks or vats, 10 by lofeet and 15 feet deep, holding upwards of 60,000 gallons of solution, for depositing copper upon rollers, hydraulic rams, and other large work. Two steam jacketed circular tanks, or cylinders, 3 feet in diameter and 15 feet deep, are used, respectively, for caustic potash ley and cyanide of copper solution, the latter being employed to give a pre- liminary coating of copper upon iron work. Above the large deposit- ing tanks is a system of overhead gearing for giving motion to the objects while in the bath, and for raising or lowering iron rollers and other heavy objects while in the bath. These heavy pieces are sus- pended from hooks, each of which is capable of sustaining a weight of five tons. The copper anodes employed for this class of work consist of ingots of copper about 4 inches square and 12 feet in length, the upper end of each ingot being furnished with a hole to admit a suspending hook. A series of tanks of considerable length are used for coppering the hydraulic rams used in graving docks for raising ships to undergo repair. At a convenient distance from the several baths the dynamo -electric machine is placed, its conducting wires, which are about one inch in thickness, being placed in connection with the various vats by suitable binding -screws or clamps. Resist- ance coils are attached to each vat, by which the power of the cur- rent entering the depositing tanks is regulated. TENSILE STEENGTH OF ELECTROLYTIC COPPER. 145 Respecting the coppering of hydraulic rams by electricity, it may be interesting to state that several years ago a series of extensive trials were made, under the inspection of the Lords of the Admiralty, to cop- per the large rams by voltaic electricity, many hundreds of cells being employed. These trials were carried on for about three years with re- peated failures, owing to the difficulty in keeping the batteries in work- ing order local action and the usual battery troubles being a continued source of hindrance in the prosecution of the work. The desired results are now obtained by means of dynamo -electricity. Tensile strength of Electrolytic Copper. The electrical engin- eers have, during the past few years, devoted special attention to the construction of dynamo -electric machines suitable for the electro - deposition of copper upon the large scale ; and after a long series of practical trials of a very extensive character, have succeeded in pro- ducing machines of extraordinary power, yielding currents of low electromotive force, capable of depositing pure copper in the finest possible condition, and possessing remarkable tensile strength. The coils of these machines are usually wound with pure electrolytic cop- per wire, insulated in the usual manner. As an evidence of the tensile strength of the copper deposited by dynamo -electric machines, we have been furnished with the following data, which prove beyond doubt the unquestionable superiority of pure electrolytic copper, when deposited under the favourable conditions of an exactly suitable current. In Molesworth's Standard Tables of the Strength of Metals, page 16, the following data are given respecting the tensile strength of copper : Tensile Strength. Copper bolts . . . iyo tons per square inch. Cast copper. ... 8-4 Sheet copper . . . 13-4 Copper wire . . . 26*0 ,, Copper wire is always most carefully and thoroughly annealed and drawn through successive holes in the draw-plate a considerable number of times, so as to produce wire possessing the highest degree of tensile strength of which ordinary copper is susceptible. In the above table, the tensile strength of sheet copper, after being subjected to the ordinary operations of annealing and rolling, is given as 13-4 tons per square inch. To show how greatly this strength has been exceeded by the fine quality of copper deposited by electrolysis, we will take the following extract from a certificate of Mr. Kirkaldy, of the Testing "Works, Southwark Street, London, respecting a sample of sheet copper deposited by the Hallett-Elmore machine, which is as follows: Test (absolute) 71830 Ibs. = 32-0 tons per square inch. The extension was given as 38-3 per cent. 146 ELECTRO-DEPOSITION OF COPPER. These figures show how remarkable is the superiority in strength of electrolytic copper, when deposited under proper conditions, as com- pared with ordinary commercial copper, a fact which must, apart from its other important attributes, create an extensive demand for copper deposited by electricity in preference to that obtained by the ordinary refining processes for all purposes, in which the strength of the metal is of the first importance, as in the case of wire, boiler tubing, &c. Amongst the many useful purposes to which some of our large elec- trolytic works are applying the deposition of copper, may be men- tioned the production of copper plates, tubes, and other hollow cylinders up to 30 feet in length, and of any required diameter (up to, say, 36 inches), and of any desired thickness. The tubing is produced at about the cost of ordinary tubing, and the tubes may be obtained in oval or any other form, or corrugated, and of unequal thickness, where it is desired, and also with flanges, in one entire piece. We have lately seen some excellent specimens of electrolytic copper tubing, about half an inch in thickness and some 14 or 15 inches in diameter, to be employed as gas checks for the Palliser gun, which appeared to us the perfection of electro -deposited copper, and when compared with tubing made from rolled and drawn copper, as ordinarily produced, really possesses, as we have seen by the foregoing test, considerably more than double the tensile strength of the latter ; moreover, when placed by the side of cast tubing (usually pitted with sand-holes of greater or less magnitude), the superiority of the electrolytic copper tubing is beyond dispute. Another important feature in the copper deposited in this form is that it is perfectly smooth on both surfaces in many cases a point of considerable im- portance and therefore needs but little turning, or other surfacing process, to render it bright when required to be so. Coppering Steel Wire for Telegraphic Purposes. It had always been held that if iron wire could be successfully and economi- cally coated with copper, it would be of incalculable service in tele- graphy ; and, indeed, many attempts to accomplish this were made at a period when magneto and dynamo -electric machines were unknown. It soon became apparent, however, that, independent of other difficulties, the object could never be practically attained by means of the voltaic battery. Now that we are enabled to obtain electricity simply at the cost of motive power, that which was impossible thirty years ago has been to some extent accomplished, and the coppering of steel wire for telegraph purposes forms an extensive branch of manufacture in con- nection with one of the telegraph systems of America. The manu- facture of " compound wire," as it is called, has been carried out on a very large scale at Ansonia, Connecticut, by the Postal Telegraph COPPEKING SOLUTIONS. 147 Company, who, Professor Silliman, of Yale College, U.S.A., states, have acquired "the largest electro -plating establishment in the world ; yet its capacity is soon to be trebled. The works are em- ployed in coppering steel wire used in the company's system of telegraphy, and now deposit two tons of pure copper per day. The steel core of the wire gives the required -tensile strength, while the copper coating gives extraordinary conducting power, reducing the electrical resistance enormously. The compound wire consists of a steel wire core weighing 200 Ibs. to the mile," n and having a tensile strength of 1650 Ibs., upon which copper is deposited, by dynamo - electricity, of any required thickness. Twenty-five large dynamo machines are employed, which deposit collectively 10,000 Ibs. of copper per day, representing 20 miles of 'compound wire,' carry- ing 500 Ibs. of copper to the mile. When the works are completed, three 300 horse-power engines will drive dynamo machines for sup- plying the current to deposit copper upon 30 miles of wire per day. In the process of deposition the wire is drawn slowly over spiral coils, through the depositing vats, until the desired thickness is obtained." The advantages of coppered steel wire over ordinary galvanised iron wire for telegraph purposes cannot well be over-estimated, and if the process prove as successful as it is stated to be, it will un- doubtedly be a great electrolytic achievement. Coppering Solutions. In preparing alkaline coppering solutions, for depositing a preliminary coating of copper upon iron, and for other purposes of electro -coppering, either of the formulae for brass- ing solutions may be used, by omitting the zinc salt and doubling the quantity of copper salt ; or either of the following formulae may be adopted. As a rule, copper solutions should be worked hot, say at a temperature of about 130 Fahr., with an energetic current, especially for cast-iron work, since even with the best solution deposition is but slow when these solutions are worked cold. It is important to bear in mind in making up copper solutions and the same observation applies with at least equal force to brassing solutions that commer- cial cyanide of potassium is largely adulterated with an excess of car- bonate of potash, and unless a cyanide of known good quality be employed, the solution will be not only a poor conductor of the cur- rent, but the anodes will fail to become freely dissolved, whereby the solution will soon become exhausted of a greater portion of its metal in the process of deposition. The cyanide to be used for making up such solutions should contain at least 75 per cent, of real cyanide. Solution i. Dissolve 8 ounces of sulphate of copper in about i quart of hot water ; when cold, add liquid ammonia of the specific gravity of -880 gradually, stirring with a glass rod or strip of wood after each addition, until the precipitate which at first forms becomes 148 ELECTRO-DEPOSITION OP COPPER. re-dissolved ; dilute the solution by adding I quart of cold water. Now prepare a solution of cyanide of potassium by dissolving about I J Ib. of the salt in 2 quarts of water, and add this gradually to the copper solution, with stirring, until the blue colour of the ammonio- sulphate entirely disappears ; finally add the remainder of the cyanide solution, and allow the mixture to rest for a few hours, when the clear liquor may be decanted into the depositing vessel or tank, and is then ready for use. This solution may be used cold, with a strong current, but it is preferable to work it at about noto 130 Fahr. Solution 2. The acetate or chloride of copper may be used instead of the sulphate in making up a coppering bath, the latter salt being preferable. Solution 3. Gore recommends a solution prepared as follows : Dis- solve cyanide of copper in a solution of cyanide of potassium, con- sisting of 2 pounds of cyanide to I gallon of water, then adding about 4 ounces more of the salt as free cyanide ; the solution is then ready, and should be worked at a temperature of about 150 Fahr. Cyanide of copper is not freely soluble in a solution of cyanide of potassium, and the liquid does not readily dissolve the anodes, nor is it a good conductor. It has also a tendency to evolve hydrogen at the cathode ; this, however, may be lessened or wholly prevented by avoiding the use of free cyanide, employing a weaker current, and adding liquid ammonia and oxide of copper. From our own experience, the addi- tion of liquid ammonia to copper solutions, if not applied in the first instance, becomes a necessity afterwards. Solution 4. Roseleur gives the following formulae for a coppering solution : 20 parts of crystallised acetate of copper are reduced to a powder, and formed into a paste with water ; to this is added 20 parts of soda crystals, dissolved in 200 parts of water, the mixture being well stirred. To the green precipitate thus formed, 20 parts of bisul- phite of sodium, dissolved in 200 parts of water, are added, by which the precipitate assumes a dirty yellow colour. 20 parts of pure cyanide of potassium, dissolved in 600 parts of water, are finally added, and the whole well stirred together. If the solution does not become colourless, an addition of cyanide must be given. It is said that this solution may be worked either hot or cold, with a moderately strong current. Dr. Eisner's Solution. In the preparation of this solution, I part of powdered bitartrate of potassium is boiled in 10 parts of water, and as much recently prepared and wet hydrated carbonate of copper, which has been washed with cold water, stirred with it as the above solution will dissolve. The dark blue liquid thus formed is next fil- tered, and afterwards rendered still more alkaline by adding a small WALENN'S COPPERING SOLUTIONS. 149 quantity of carbonate of potash. This solution is stated to be appli- cable to coating iron, tin, and zinc articles.* Walenn's Coppering Solution. This solution, to be employed for coppering 1 iron, consists in dissolving cyanide of copper in a solu- tion composed of equal parts of cyanide of potassium and tartrate of ammonia. Oxide of copper and ammoniuret of copper are added in sufficient quantity to prevent the evolution of hydrogen at the surface of the work during deposition. The solution is worked at about 180 Fahr. The current from one Smee cell may be used with this solution. It has been found that if- ounce of copper per square foot will pro- tect iron from rust. Another process of Mr. Walenn's is as follows : The first part of this invention "relates to electro -depositing copper upon iron, or upon similar metals, so that the coating may be soft and adherent. This consists in using the solution at a boiling heat, or near thereto, namely, from 150 Fahr. to the boiling point of the solution. The second part is to prevent the evaporation of a solution which is heated during deposition. A cover, with a long condensing worm tube, is used in the depositing bath ; the other end of the tube opens into a box containing materials to condense or appropriate the gases that escape. The liquids flow back down the tube into the tank. The third part of the invention consists in working electro -depositing solutions in a closed vessel under known pressure, being applied by heating the solution or otherwise. The closed vessel may be used for solutions in which there is free ammonia, or where other conditions arise in which it is necessary to enclose the solution, although neither appreciable increase of pressure arises nor is heat applied. If there be much gas coming off, the condensing tube, opening into a box of the second part of the improvements, maybe employed." The fourth part of the invention consists in adding to the charged, and fully made, copper, brassing, or bronzing solution, cupric ammonide in the cold, until the solution is slightly green. Gulensohn's Process. A bath is made by first obtaining a solution of chloride of copper, the metal from which is precipitated in the form of phosphate, by means of pyrophosphate of soda. The precipitate is then thoroughly washed until all traces of the chloride of soda formed have been removed ; the phosphate of copper is next dissolved in a solution of caustic soda, and, if necessary, a small quantity of liquid ammonia is added to assist the solution of the phosphate, and to render the deposit brighter and more solid. The strength of the solution must be regulated according to the strength of the current * The Chemist, vol. vii. p. 124. I5O ELECTRO-DEPOSITION OF COPPER. employed in the deposition. The bath may be used for depositing upon iron or other metals. "Weil's Coppering Processes. (i.) For coating large objects, as cast-iron fountains, lamp-posts, &c. M. Weil's patent gives the fol- lowing process: Dissolve in 1,000 parts of water, 150 of sodio- potassic tartrate (Eochelle salt), 80 of caustic soda, containing from 50 to 60 per cent, of free soda, and 35 of sulphate of copper. Iron and steel, and the metals whose oxides are insoluble in alkalies, are not corroded in this solution. The iron or steel articles are cleaned with dilute sulphuric acid, of specific gravity 1*014, by immersing them in that liquid from five to twenty minutes, then washing with water, and finally with water made alkaline by soda. They are next cleaned with the scratch-brush, again washed, and then immersed in the cupreous bath, in contact with a piece of zinc or lead, or suspended by means of zinc wires ; the latter is the most economical way. The articles must not be in contact with each other. They thus receive a strongly -adherent coating of copper, which increases in thickness (within certain limits) with the dura- tion of immersion. Pure tin does not become coppered by contact with zinc in this solution ; it oxidises, and its oxide decomposes the solution, and precipitates red sub-oxide of copper, and by prolonged action, all the copper is thus removed from the liquid. The iron articles require to be immersed from three to seventy -two hours according to the colour, quality, and thickness of the required deposit. The copper solution is then run out of the vat, and the coated articles washed in water, then cleaned with a scratch-brush, washed, dried in hot sawdust, and lastly in a stove. To keep the bath of uniform strength, the liquid is renewed from below, and flows away in a small stream at the top. After much use, the exhausted liquid is renewed by precipitating the zinc by means of sulphide of sodium (not in excess), and re-charging the solution with cupric sulphate. Weil also supplies to the bath hydrated oxide of copper. (2.) A coppering bath is prepared as follows : 35 parts of crystal- lised sulphate, or an equivalent of any other salt of copper, are precipitated as hydrated oxide by means of caustic soda or potash. The oxide of copper is to be added to a solution of 150 parts of Bochelle salt, and dissolved in 1,000 parts of water. To this, 60 parts of caustic soda, of about 70 per cent., is to be added, when a clear solution of copper will be obtained. Other alkaline tartrates may be substituted for the Rochelle salt above mentioned, or even tartaric acid may be employed ; but in the case of tartaric acid, or acid tartrates, a small additional quantity of caustic alkali must be added, sufficient to saturate the tartaric acid or acid tartrate. Oxide of copper may also be employed, precipitated by means of a hypochlorite, but in all ELECTRO-ETCHING. I 5 1 cases the proportions between the copper and tartaric acid should be maintained as above, and it is advantageous not to increase to any notable extent the proportion of the caustic soda. The object to be coppered is to be cleaned with a scratch-brush and then placed in the bath, when it will become rapidly coated with an adherent film of metallic copper. As the bath gradually loses its copper, oxide of copper as above prepared should be added to main- tain it in a condition of activity, but the quantity of copper introduced should never exceed that above prescribed, as compared with the quantity of tartaric acid the bath may contain. If the copper notably exceeds this proportion, certain metallic iridescences are produced on the surface of the object. These effects may be employed for orna- mental and artistic purposes. According to the time of the immersion, the strength of the current, and the proportion of copper to the tartaric acid, these iridescences may be produced of different shades and tints, which may be varied or intermingled by shielding certain parts of the object by a coating of paraffin or varnish, the iridescent effect being produced on the parts left exposed. All colours, from that of brass to bronze, scarlet, blue, and green, may be thus produced at will. Electro-Etching. When we bear in mind the fact that, with few exceptions, the anodes employed in electrolytic processes become dis- solved in the bath during electro -deposition, it is evident that if certain portions of an anode were protected, by means of a suitable varnish, from the solvent action of the solution, that such parts, after the plate had been subjected to electro -chemical action in the bath, would, on removal of the varnish, appear in relief, owing to the exposed surfaces having been reduced in substance by being partially dissolved in the solution. Suppose a smooth and bright plate of cop- per, for instance, were to have a design sketched upon it with a suitable varnish, and the plate then connected to the positive electrode of a voltaic battery and immersed in a solution of sulphate of copper, a cathode of the same metal being suspended from the negative elec- trode ; if, after a few hours' immersion, the plate be taken from the bath, and the varnish removed, the design will appear in bright re- lief, while the unvarnished parts will have been eaten away, or dissolved, leaving hollows of a comparatively dull appearance ; the design now forms a printing surface, from which copies may be im- pressed upon paper in the usual way. The process of voltaic etching is performed in various ways, but the following will explain the general principle upon which the art is con- ducted. A copper wire is first soldered to the plate, and the back is then coated with a tough varnish ; when this is dry, the face of the plate is coated with engraver's " etching -ground," a composition of beeswax 5 parts, linseed oil I part, melted together ; it is sometimes 152 ELECTRO-DEPOSITION OF COPPER. the practice to smoke the surface, before applying the etching needle, in order to render its tracings more visible. The design is then drawn upon the face of the plate, cutting through to the clean surface of the copper. When the etching is complete, the plate is made the anode in a sulphate of copper bath, while a plate of copper is im- mersed as the cathode. The electric current, passing out of the engraved lines, causes the copper to be dissolved from them, whereby they become etched, much in the same way, and with the same effect, as when acid is used in the ordinary etching process. ' ' The various gradations of light and shade are produced by suspending cathodes of different forms and sizes opposite the plate to be etched, in various positions, and at different distances from it, thus causing the plate to be corroded to unequal depths in different parts, the deepest action being always at those portions of the electrodes which are nearest to- gether." Gore. Instead of using wax, or other etching -ground, as an insulating material, the plate may be coated with a film of some metal which will not be dissolved in the bath. For example, the plate may be first strongly gilt by electro -deposition, and the design then produced by means of a graver, the tool cutting just sufficiently deep to expose the copper ; if now the plate be used as an anode, the copper will become dissolved, as before, leaving the gilt surface unacted upon, since the sulphuric acid set free during the voltaic action has no effect upon gold. Again, the design may be made with lithographic ink or varnish, and the exposed parts of the plate then strongly gilt ; if, thereafter, the varnish, or other insulating material be cleaned off the plate, the voltaic etching will follow the ungilt portions, causing them to be- come hollowed out as before. The baths used for etching by electrolysis should be composed of the same metal as that to be etched ; thus, a sulphate of copper bath is employed for etching copper plates, sulphate of zinc for zinc plates, and gold or silver solutions when their metals are to be treated in the same way. Copper and zinc plates, however, may be etched by means of the voltaic battery, in dilute solutions of nitric, sulphuric, hydrochloric, or acetic acid, a process which is said to be coming very much into practice. Glyptography. This process was invented by Mr. E. Palmer, and consists in first staining copper plate black on one side, over which a very thin layer of a white opaque composition, resembling white wax, is spread. The plate is then drawn upon with various etching needles in the usual way, which remove portions of the white composition, by which the blackened surface becomes exposed, forming a strong con- trast to the surrounding white ground. When the drawing is com- plete, it is carefully inspected, and then passes into a third person's MAKING ELECTROTYPE PLATES FROM DRAWINGS. 153 hands, " by whom it is brought in contact with a substance having- a chemical affinity for the remaining portions of the composition, by whom they are heightened, ad libitum. Thus, by careful manipula- tion, the lights of the drawing become thickened all over the plate equally. . . . The depths of these non -printing parts of the block must be in some degree proportionate to their width ; consequently the larger breadths of lights require to be thickened on the plate to a much greater extent. It is indispensably necessary that the printing surfaces of the block prepared for the press should project in such relief from the block itself as shall prevent the inking roller touch- ing the interstices ; this is accomplished in wood engraving by cutting out these intervening parts, which form the lights of the print, to a sufficient depth ; but in glyphography the depth of these parts is formed by the remaining portions of the white composition on the plate, analogous to the thickness or height of which must be the depth on the block, seeing that the latter is in fact a cast or reverse of the former." The plate, thus prepared, is well plumbagoed all over, and is then placed in a sulphate of copper bath, and a deposit of sufficient thick- ness obtained, which, on being separated, will be found to be a perfect cast of the drawing which formed the cliche. The metallic plate thus obtained is afterwards backed up with solder and mounted in the same way as a stereotype plate, and is then ready for the printing press. Making Copper Moulds by Electrolysis. A drawing is made upon a varnished copper plate, as before described ; the plate is then dipped into a weak * ' quicking ' ' solution, and then laid upon a flat and level surface. The mercury attacks the surfaces exposed by the graver or etching needle, and takes the meniscus, or curved form, that is, the relief is greater as the etching lines are larger ; the drawing, therefore, is reproduced in relief by the mercury. The plate is next covered with a thin paste of plaster of Paris, and when this has set, the two moulds are to be separated. A counter mould may now be taken from this, or it may be prepared in the usual way, and, after being well plumbagoed, receive a deposit of copper. By the following plan a mould is produced, which is at once ready for the bath. A copper plate is varnished and etched as before. A neutral solution of chloride of zinc is then poured upon the plate, and after this a quantity of fusible metal, which melts at from 175 to 212 Fahr. The flowing of the fusible metal over the surface of the plate is aided by the application of a spirit-lamp held beneath the plate, or by spreading the metal over the surface with a hot iron rod. The mould thus obtained may then be reproduced by the ordinary electrotype process. Making Electrotype Plates from Drawings. This invention relates to an improved process of forming matrices of designs for the 154 ELECTRO-DEPOSITION OF COPPER. production of electrotype plates directly by tlie hand of the artist or designer, in which the design is produced by means of a pointed tool upon a thin sheet of soft metal supported upon a peculiar backing of semi-plastic inelastic material of sufficient body or consistence to sup- port the metal without pressure, but sufficiently yielding to give to the slightest touch of the artist, and allow the material to be depressed under the tool for the formation of the lines of design. In carrying out this invention a mixture is made of plaster of Paris I lb., chro- mate of potassa j oz., and common salt, I oz., which forms a com- pound that will give the most delicate touch of the artist, and will allow the finest lines to be produced upon the metal by the tool. These ingredients may be mixed in various proportions, which will depend somewhat upon the boldness or delicacy of the design to be produced. The mixture may be brought to a semi-plastic state by the addition of about I pint of water, or sufficient to bring it to the proper consistence, and the plasticity of the compound may be modi- fied to suit various requirements by using more or less water. The semi-plastic composition is moulded or otherwise formed into a flat tablet of suitable size, and a sheet of soft metal is carefully secured on the upper face of same, projecting edges being left, which are after- wards turned down over the sides of the tablet. The metal is then ready for the artist, who, with a pointed tool or tools, produces the required design by indenting the lines thereon. Wherever touched by the tool the metal will be depressed into the backing, which has just sufficient body to support the untouched parts, but yields to the slightest pressure of the tool. "When the design is finished, the metal is carefully removed from the backing, having the design in relief on one side and in intaglio on the other, and is ready for the production of the electrotype plate in the ordinary way, which may be taken from either side, as circumstances require. Coppering Steel Shot. The electro -deposition of copper is being extensively applied by the Nickel Plating Company, Greek Street, Soho, London, to the coating of large and small steel shot with copper for the Nordenfelt gun. Coppering Notes. I. In preparing cast-iron work for electro- coppering, after the pieces have been pickled and scoured, they should be carefully examined for sand-holes, and if any such cavities appear upon the work, they must be well cleared from black or dirty matter, which may have escaped the brushing, by means of a steel point. It must always be borne in mind that copper, and indeed all other metals, refuse to deposit upon dirt. After having cleared out the objectionable matter from the sand-holes, and again well brushed the article with sand and water, it is a good plan to give the piece a slight coating of copper in the alkaline bath, and then to examine it again, when if COPPERING NOTES. 155 any cavities show signs of being foul, they must be cleared with the steel point as before. The article should then have a final brushing with moist sand, and after well rinsing be placed in the alkaline coppering bath and allowed to remain, with an occasional shifting of position, until sufficiently coated. If the piece of work is required to have a stout coating of copper, it should receive only a moderate deposit in the cyanide bath, and after being well rinsed suspended in the sulphate of copper, or acid bath, as it is sometimes termed, and allowed to remain therein until the desired coating is obtained. To secure an uniform deposit, however, the object should be occasionally shifted while in the bath, except when mechanical motion is applied, as in coppering iron rollers and other similar work. 2. Respecting the working of copper solutions, Gore makes the following observations : "If the current is too great in relation to the amount of receiving surface, the metal is set free as a brown or nearly black metallic powder, and hydrogen gas may even be deposited with it and evolved. In the sulphate solution, if the liquid is too dense, streaks are apt to be formed upon the receiving surface, and the article (especially if a tall one) will receive a thick deposit at its lower part, and a thin one at the upper portion, or even have the deposit on the upper end redissolved. If there is too little water, crystals of sulphate of copper form upon the anode, and sometimes even upon the cathode, at its lower part, and also at the bottom of the vessel. If there is too much acid the anode is corroded whilst the current is not passing. The presence of a trace of bisulphide of carbon in the sulphate solution will make the deposit brittle, and this continues for some time, although the solution is continually deposit- ing copper ; in the presence of this substance the anode becomes black, but if there is also a great excess of acid, it becomes extremely bright. Solutions of cupric sulphate, containing sulphate of potassium, and the bisulphide of carbon applied to them, are sometimes employed for depositing copper in a bright condition. The copper obtained from the usual double cyanide of copper and potassium solution, by a weak current, is of a dull aspect, but with a strong current it is bright." For depositing copper from alkaline solutions, we prefer the Bunsen battery to all others. 3. The anodes used in electrotyping, as also those employed for depo- siting copper generally, should consist of pure electrolytic copper, in preference to the ordinary sheet metal, which invariably contains small traces of arsenic and other metals, which are known to diminish its conductivity considerably. Clippings and other fragments of cop- per from electrotypes may be used up as anodes, either by suspending them in a platinum-wire cradle or in a canvas bag, the fragments being put in connection with the positive electrode of the battery by 156 ELECTRO-DEPOSITION OF COPPER. means of a stout rod or strip of copper. These make-shift anodes, however, should be used for thickening the deposit (if an electrotype) after the mould is completely coated with copper, and not in the earlier stage of the process. 4. When it is desired to obtain an electrotype of considerable thick- ness, this may be hastened in the following way : After the complete shell is obtained, clean copper filings are to be sifted over the surface, and deposition allowed to proceed as usual, when the newly deposited metal will unite with the copper filings and the original shell, and thus increase the thickness of the electrotype. By repeated additions 'of copper filings, followed by further deposition of copper, the back of the electrotype may be strengthened to any desired extent. 5. For coating with copper non-conducting substances, such as china or porcelain, the following process has been adopted in France : Sulphur is dissolved in oil of spike lavender to a sirupy consistence, to which is added-either chloride of gold or chloride of platinum, dissolved in ether, the two liquids being mixed under gentle heat. The com- pound is next evaporated until it is of the consistency of ordinary paint, in which condition it is applied with a brush to such parts of a china or porcelain article as it is desired to coat with copper ; the article is afterwards baked in the usual way, after which it is immersed and coated with copper in the ordinary sulphate bath. CHAPTER XII. DEPOSITION OF GOLD BY SIMPLE IMMERSION. Preparation of Chloride of Gold. Water Gilding. Gilding by Immersion 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. Preparation of the Work for Gilding. Gilding by Contact with Zinc, Steele's Process. Gilding with the Eag. Preparation of Chloride of Gold. Since for all gilding purposes "by the wet way, as we may term it in contradistinction to the process of mercury gilding, this metal requires to be brought to the state of solution, it will be well to explain the method of preparing the salt of gold commonly known as the chloride of gold, but which is, strictly speaking, a terchloride of the metal, since it contains three equivalents of chlorine. The most convenient way of dissolving the precious metal is to carefully place the required quantity in a glass flask, such as is shown in Fig. 70, and to pour upon it a mixture consisting of about 2 parts of hydrochloric acid and I part nitric acid by measure. This mixture of acids was called aqua regia by the ancients because it had the power of dissolving the king of metals gold. To dissolve I ounce of gold (troy weight) about 4 ounces of aqua regia will be required, but this will depend upon the strength of the commercial acids. Soon after the mixed acids have been poured on the gold, gas is evolved, and the chemical action may be accelerated by placing the flask upon a sand-bath moderately heated. It is always advisable, when dissolving this or other metal, in order to avoid excess of acid, Fig. 70. to apply less of the solvent than the maximum quantity in the first instance, and, when the chemical action has ceased, to pour off the dissolved metal and then add a further portion of the solvent to the remainder of the undissolved metal, and so on 158 DEPOSITION OF GOLD BY SIMPLE IMMEESION. until the entire quantity is ;dissolved without any appreciable excess of acid, after which the various solutions are to be mixed together. The solution of chloride of gold is to be carefully poured into a porcelain evaporating dish* (Fig. 71), and this, placed on a sand-bath or otherwise, gently heated until nearly all the acid is expelled, when the solution will assume a reddish hue. At this period the author prefers to move the evaporating dish round and round gently so as to spread the solution over a large surface of the interior of the vessel ; in this way the evaporation of the acid is hastened considerably. When the solution assumes a blood- red colour the dish should be gently, but repeatedly, moved about as before until the semi-fluid mass Fig. 71. which gradually becomes deeper in colour and more dense in substance ceases to flow. Towards the end of the operation the last remaining fluid portion flows torpidly, like molten metal, until it finally ceases altogether, at which moment the dish should be removed from the sand-bath and allowed to cool. It is necessary to mention that if too much heat be applied when the solution has acquired the blood-red colour the gold will quickly become reduced to the metallic state. If such an accident should occur the reduced metal, after dissolving out the chloride with distilled water, must be treated with a little aqua regia, which will again dissolve it. The red mass resulting from the above operation (if properly con- ducted) is next to be dissolved in distilled water, in which it is readily soluble, and should form a perfectly clear and bright solution of a brownish-yellow colour. If, on the other hand, the evaporation has not been carried to an extent sufficient to expel all the acid the solu- tion will be of a pure yellow colour. It invariably happens, after the chloride of gold is dissolved in water, that a white deposit re- mains at the bottom of the evaporating dish this is chloride of silver, resulting from a trace of that metal having been present in the gold. Water- Gilding. Previous to the discovery of the electrotype pro- cess and the kindred arts of electro -gilding and silvering to which it gave rise, a process was patented by Mr. G-. R. Elkington for gilding metals by the process of simple immersion or "dipping," and this process, which acquired the name of water-gilding, was carried on by Messrs. Elkington at Birmingham for a considerable time with success for a certain class of cheap jewellery. The solution was pre- pared as follows : A strong solution of chloride of gold was first obtained, to which acid carbonate of potash was added in the propor- tion of I part of the metal to 31 parts of the acid carbonate ; to this mixture was added 30 parts more of the latter salt previously dis- * Evaporating dishes made from Berlin porcelain are the best for this purpose, since they are not liable to crack when heated. SOLUTION FOR GILDING SILVER. 1 59 solved in 200 parts of water. The mixture was then boiled for two hours, during which period the solution, at first yellow, assumed a green colour, when it was complete. To apply the above solution the metal articles, of brass or copper, are first well cleaned and then immersed in the solution, which must be hot, for about half a minute. Articles of silver or German -silver to be gilt in this solution must be placed in contact with either a copper or zinc wire. Gilding by Immersion, in a Solution of the Chloride of Gold. Articles of steel, silver, copper, and some other of the baser metals, may be gilt by simply immersing them in a weak solution of the chloride of gold ; this is, however, more interesting as a fact than of any practical value. Gilding by Immersion in an Ethereal Solution of Gold. Chloride of gold is soluble in alcohol and in ether. The latter solu- tion may be obtained by agitating a solution of gold with ether, after which the mixture separates into two portions ; the upper stratum, which is of a yellow colour, is an ethereal solution of chloride of gold, while the lower stratum is merely water and a little hydrochloric acid. Steel articles dipped in the ethereal solution become instantly covered with gold, and, at one time, this method of gilding steel was much employed for delicate surgical instruments, as also for the orna- mentation of other articles of steel. After being applied, the ether speedily evaporates, leaving a film of gold upon the object. If the ethereal solution be applied with a camel-hair brush or quill pen, initials or other designs in gold may be traced upon plain steel surfaces. Or, if certain portions of a steel object be protected by wax or varnish, leaving the bare metal in the form of a design, the ethereal solution may then be applied to the exposed surfaces, which will appear in gold when the wax or varnish is dissolved or otherwise cleared away. Various ways of applying this solution for the orna- mentation of steel will naturally occur to those who may be desirous of utilising it. Solution for Gilding Brass and Copper. The following formula has been adopted for " water -gilding " as it is termed : Fine gold 6J dwts. Convert the gold into chloride, as before, and dissolve it in I quart of distilled water, then add Bicarbonate of potassa . . . . i lb. and boil the mixture for two hours. Immerse the articles to be gilt in the warm solution for a few seconds up to one minute according to the activity of the bath. Solution for Gilding Silver. Dissolve equal parts, by weight, of bichloride of mercury (corrosive sublimate) and chloride of ammonium l6o DEPOSITION OP GOLD BY SIMPLE IMMERSION. (sal-ammoniac), in nitric acid ; now add some grain gold to the mixture and evaporate the liquid to half its bulk ; apply it, whilst hot, to the surface of the silver article. Solution for Gilding Bronze, &c. A preparatory film of gold may be given to large bronze articles that are to be fully gilt by either of the processes hereafter described, or small articles of " cheap" work may be gilt by immersing them in the following solution, which must be used at nearly boiling heat : Caustic potash . . . . 180 parts Carbonate of potash ... 20 Cyanide of potassium ... 9 Water 1,000 Rather more than i| part of chloride of gold is to be dissolved in the water, when the other substances are to be added and the whole boiled together. The solution requires to be strengthened from time to time by the addition of chloride of gold, and also, after being worked four or five times, by additions of the other salts in the pro- portions given. This bath is recommended chiefly for gilding, economically, small articles of cheap jewellery, and for giving a pre- liminary coating of gold to large articles, such as bronzes, which are to receive a stronger coating in the pyrophosphate bath described further on, or in cyanide solutions by aid of the battery. In this bath articles readily receive a light coating of gold, and it will con- tinue to work for a very long period by simply adding, from time to time as required, the proper proportions of gold and the other sub- stances comprised in the formula. By keeping the bath in proper order a very large number of small articles may be gilt in it at the expense of a very small proportion of gold. Another method of gilding by simple immersion, applicable to brass and copper articles, is to first dip them in a solution of pro to - nitrate of mercury (made by dissolving quicksilver in nitric acid and diluting with water), and then dipping them into the gilding liquid this plan being sometimes adopted for large articles. It is said that copper may be gilded so perfectly by this method as to resist for several hours the corrosive action' of concentrated acids. The secret of the action is that the film of mercury, being electro- positive to the gold, dissolves in the auriferous solution and deposits a film of gold in its place. Gore. French Gilding for Cheap Jewellery. The bath for gilding by dipping, recommended by Roseleur, is composed of Pyrophosphate of soda or potassa . . 800 grammes. Hydrocyanic acid of J (prussic acid) . 8 Chloride of gold (crystallised) . . . 20 Distilled water , . . . 10 litres. PBENCH GILDING. l6l The pyrophospliate of soda is generally employed, and this may be prepared by melting, at a white heat, ordinary crystallised phosphate of soda in a crucible. The quantity of gold given in the above formula represents the grammes of the pure metal dissolved by aqua regia. In making up the bath, 9 litres of water are put into a por- celain or enamelled-iron vessel, and the pyrophosphate added, with stirring, a little at a time, moderate heat being applied until all the salt is dissolved. The solution is then to be filtered and allowed to cool. The chloride of gold must not be evaporated to dryness, as previously described, but allowed to crystallise ; the crystals are to be dissolved in a little distilled water, and the solution filtered to keep back any chloride of silver that may be present in the dissolving flask, derived from the gold. The filter is next to be washed with the remainder of the distilled (or rain) water. The chloride solution is now to be added to the cold solution of pyrophosphate of soda, and well mixed by stirring with a glass rod. The hydrocyanic acid is then to be added, with stirring, and the whole heated to near the boiling point, when the solution is ready for use. If the pyrophos- phate solution is tepid, or indeed in any case, Eoseleur thinks it best to add the prussic acid before the solution of chloride of gold is poured in. The employment of prussic acid in the above solution is not absolutely necessary, indeed many persons dispense with it, but the solution is apt to deposit the gold too rapidly upon articles immersed in it, a defect which might be overcome by employing a weaker solu- tion. If the solutions are cold when mixed, the liquor is of a yellow- ish colour, but it should become colourless when heated. It sometimes happens that the solution assumes a wine-red colour, which indicates that too little prussic acid has been used ; in this case the acid must be added, drop by drop, until the solution becomes colourless. An excess of prussic acid must be avoided, since it has the effect of retarding the gold deposit upon articles immersed in the solution. The proper con- dition of the bath may be regulated by adding chloride of gold when prussic acid isi n excess, or this acid when chloride of gold predomi- nates. In this way the bath may be rendered capable of gilding without difficulty, and of the proper colour. Eespecting the working of this solution, Eoseleur says, " The bath will produce very fine gilding upon well- cleaned articles, which must also have been passed through a very diluted solution of nitrate of mercury, without which the deposit of gold is red and irregular, and will not cover the soldered portions. The articles to be gilded must be constantly agitated in the bath, and supported by a hook, or placed in a stoneware ladle perforated with holes, or in baskets of brass gauze, according to their shape or size." In gilding by dipping, it is usual to have three separate baths 1 62 DEPOSITION OF GOLD BY SIMPLE IMMERSION. placed in succession, and close to each other, all being heated upon the same furnace by gas or otherwise. The first bath consists of an old and nearly exhausted solution in which the articles are first dipped to free them from any trace of acid which may remain upon them after being dipped in aqua fortis. The second bath, somewhat richer in gold than the former, is used for the next dipping, and the articles then receive their final treatment in the third bath. By thus working the baths in rounds, " the fresh bath of to-day becomes the second of to-morrow, and the second takes the place of the first, and so on. This method of operating allows of much more gilding with a given quantity of gold than with one bath alone," and con- sequently is advantageous both on the score of economy and con- venience. The gilding is effected in a few seconds, when the articles are rinsed in clear water and dried by means of hot sawdust, prefer- ably from white woods ; they are afterwards burnished if necessary. Roseleur does not approve of boxwood sawdust for this purpose, since it is liable to clog the wet pieces of work, besides being less absorbent than the sawdust of poplar, linden, or fir. The sawdust should neither be too fine nor too coarse, and kept in a box with two par- titions, with a lining of zinc at the bottom. The box is supported upon a frame of sheet- iron or brickwork, which admits, at its lower part, of a stove filled with bakers' charcoal, which imparts a gentle and uniform heat, and keeps the sawdust constantly dry. After drying very small articles in sawdust, they are shaken in sieves of various degrees of fineness, or the sawdust may be removed by winnow- ing. The above process of gilding by dipping, or "pot gilding," as it was formerly called, is applied to articles of cheap jewellery, as bracelets, brooches, lockets, &c., made from copper or its alloys, and has been extensively adopted in France for gilding the pretty but spurious articles known as French jewellery. Colouring Gilt Work. In working gold solutions employed in the dipping process, it may sometimes occur that the colour of the de- posit is faulty and patchy instead of being of the desired rich gold colour. To overcome this, certain " colouring salts " are employed, the composition of which is as follows : Nitrate of potash . . -^ Sulphate of zinc . . f Sulphate of iron . . > * 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- FKENCH GILDING. 1.6s 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. Roseleur 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-moultiing 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. Eoseleur. 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, 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- CRUET 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 246 ELECTRO-DEPOSITION OF SILVEE. 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-BKUSHING. 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 ivliitcning 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 Fig. 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 in 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 revolvin g 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 pj 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 DYNAMOELECTKICITY. 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. Koseleur'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. Replatiug 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 manufactured 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 extremo 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 bo 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 desihered, 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 "lead edges," as they are properly called. Some persons remove them alto- gether, and replace them by brass mounts, which are specially sold for 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 ARTICLES. 255 till ; 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. Erom 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 ELECTKO-DEPOSITION OF 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 run out 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 filling 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-stone ; 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 stripped, 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 bimg, 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 258 ELECTRO-DEPOSITION OF 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 neccs- CHARACTERISTICS OF ELECTKO-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 sjrewed 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 4 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 i;-reatly 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 ure then to be potashed, quicked, plated, and finished in the same way ;is 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- diato effect upon nickel, will soon set the mind at rest upon this point. 20O ELECTKO-DEPOSITION OF SIFTER. 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 put* his mark upon the 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 1 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. Koseleur'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 time 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 OF 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 ELECTRO-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." This is quite true, but when electro -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 ELECTKC-DEPOSITION OF SILVER. "When the same articles are required to \>Q fully well plated, the pro- portions should be about as follows : For coffee and teapot, about ij 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 J 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 name, 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 us 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 iu 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 tern - 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 fume.-; 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 bo 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 ichitening. 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. cientiy 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 27O IMITATION ANTIQUE SILVER. being suitable for small surfaces. In applying either of the materials the article should be quite dry, 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 PROCESSES. 27! 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 SILVER. 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 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, OK NIELLED SILVEK. 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 w 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. Koseleur 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 samp 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. Pink 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. if 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 SILVERING 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 the 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. Respecting the improper use of cyanide, &c., by depositors, Gore gives the following amusing experiences of some electro -platers : "One discovered that the operator, by using cyanide of potassium, regardless of its strength, to make cyanide of silver, redissolved 276 IMITATION ANTIQUE SILVER. about sixty ounces of silver, and threw it away in the wash-waters. Another had a similar mishap with eleven ounces of gold. A third had 450 ounces of silver converted into waste residue. A fourth had two large vats of silver solution rendered incurable by addition of too much ' brightening ' liquid, and many electro -platers have had similar mishaps. Others have found that their anodes dissolve with extraordinary rapidity, through the use of too much free cyanide, or by allowing them to remain in contact with the iron vat, and have been surprised to find that a solution which, when made, contained only one ounce of silver per gallon, held in solution more than four times as much. Others, by keeping a record of the silver dissolved and deposited, as well as that found in the liquid by analysis, have missed a considerable quantity, and ultimately found that it had soaked into the sides of the thick wooden vats." 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 . Cleaning 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 Peivter 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. Q. Metal Tanlcs. "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 27^> 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 hath, 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 XXL ELECTEO -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 days 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, and should never be allowed to enter the nickel bath. The 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|-inch 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 n 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 S- 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 1 20 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. loo 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 ' I00 ' between the coppei hook and the anode, the author has found it very advantageous to unite the two by means of pewter scldtr, in the following way,* and which it may be useful to quote here: The holes " Electro-Metallurgy Practically Treated." By Alexander Watt. IEEPAEATION OF NICKEL SOLUTIONS. 2 03 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. 101. A pair of carbon plates are united by a clamp, with binding screw attached, as shown in Fig. i. A plate TWIN-CARBON BATTERY. 285 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 ceU is Fig. 101. 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 2 86 ELECTRO-DEPOSITION OF 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 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, OR 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 haa 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 2 88 ELECTKO-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 from the dipping acid. 290 ELECTRO-DEPOSITION OP 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) . . . . } Ib. 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 folio whig 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. ELECTEO-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, with 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, which runs as follows : 292 ELECTRO-DEPOSITION OP 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 1 , 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 as 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 acM 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^ 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 i -05 2 (water rooo), 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 evaporated to dryness ; it should be rendered as anhydrous as possible. The salt is then place 1 in a retort, and heated to a bright red heat. The salt sublimes, and is collected in a suitable receiver, the earthy 294 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-ioo." 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. TJnwin'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 i'4OO), one part of strong sulphuric acid (sp. gr. about I '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 gram 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 small 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 not UNWIN S PROCESS. 2Q5 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 u 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 . . . . . 2 J 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 ammonium 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 ii Water 200 3. Phosphate of nickel 10 parts. Citrate of nickel 6 Pyrophosphate of sodium ioj Bisulphite of sodium ij 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 1880, 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 PBOCESS. 297 with ' ' the addition of sufficient free acetic acid to render the solution distinctly acid." The formula is given below : Acetate of nickel 2f 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. i'O47. Mr. Potts first precipitates the carbonate of nickel from a boiling aqueous solution of the sulphate, by the addition of bicarbonate of soda, then filters 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 3 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 w 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 unf requently occurs that a nickel-plater receives a sword and sheath with instruction to nickel tlia latter only. When such is the case, the sword should be with- 316 ELECTBO-DEFOSITION 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 HAENESS FUENITUEE, 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. pound of ELECTRO-DEPOSITION OF NICKEL. sulphuric acid to each gallon of water used to make up the bath. ]ja 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, I1 5- are cut while 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 RE-NICKELING OLD WORK. 319 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. Be -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 great 32O ELECTRO-DEPOSITION OF 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 in 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 tune 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 more durable. The rollers are first Y 322 ELECTRO-DEPOSITION OF 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 the finish 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 used 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. 322 ELECTRO-DEPOSITION OF 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 maybe 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 the finish 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 Ar ticks. 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 used 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 ELECTKO-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. Un win'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 Alexan der 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. 11. 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 ringers 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-marks 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 in 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 contrivances by which articles have been supported in the bath have been used many times, they en I 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 Hath. 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 p. 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 f orated 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. Hotted 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 2 50 -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 rolled 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 ELECTRO-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 objectionable 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. THEEE 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) ... 2jfe 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 OP TIN. The chloride of tin (which may be obtained at the drysalters) is readily made by dissolving 1 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 1 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, 375; alumina, H'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 ROSELEURS 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 being 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. Roseleur 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 OF 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. Hillier'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. He er en'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 OP 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. 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 Fig. 118. * Electro-Metallurgy." Eighth edition, p. 241. 336 DEPOSITION AND ELECTKO-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 as 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 is 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 placed 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 E-oseleur, " 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 silver, which may be rendered bright either by scratch -brushing or by burnishing. An intense current is necessary in working this solution. Fearrfs 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 no 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- 3$8 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 RECOVERY OF TIN FROM TIN SCRAP BY ELECTROLYSIS. 339 1 2 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 J 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 Germany, 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. Jacobi 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. Electrolytic Zinc as a Printing Surface. 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. Although iron metal may be readily deposited from a solution of its most common salt, the sulphate, or green copperas, there are other solutions from which a deposit of a more reguline character may be obtained. Gore says that he has deposited iron in the state of regu- line white metal "by passing a current of considerable intensity (from fifteen to twenty Smee's cells) for one hour, through an anode KLEIN'S PKOCESS FOB DEPOSITING IRON UPON COPPER. 341 of iron immersed in a saturated aqueous solution of sal-ammoniac ; its appearance when deposited from this liquid is rather white, very similar to that of freshly -broken cast-iron. By similar means it may also be deposited, using a saturated solution, either of carbonate of ammonium, acetate of ammonium, or acetate of potassium. Good metal may also be deposited from a saturated aqueous solution of a mixture of two parts of protosulphate of iron and one of sal-ammo- niac. I have deposited it from an aqueous solution of ferrate of potassium, formed either by igniting peroxide of iron very strongly for some minutes with caustic potash and saltpetre, and dissolving the product in water ; or by making a very strong solution of caustic potash, immersing in it a large iron or steel anode, and a small copper or platinum cathode, and passing a strong current from fifteen or twenty Smee's cells through it until it acquires a deep amethystine or purple colour ; by that time the cathode will have obtained a coating of iron, which will be in the state of a dark powder if the power has been too great, or it will have the appearance of white cast iron (or intermediate between that and the appearance of reguline deposited zinc) if the power has been sufficiently weak." This solution, how- ever, rapidly decomposes, and would not, therefore, be of any practical use. 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 the 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 Solution. Dissolve a fragment of phosphorus half -an - inch 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. 4 ' Silver Solution. 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 of 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 me^al 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 : Amxnonio -sulphate 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 ttirbid, 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 (shange 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 34 6 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 readily 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 solutions of the acetate or tartrate of zinc. Gore says that "a solution of one -part of the sulphate in five to ten of water, with a large zinc anode, may be made to yield a good deposit by a current from two small Smee's cells feebly charged." Person and Sire's Solution. This consists of a mixture of I 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. Electrolytic Zinc as a Printing Surface. The Electro -Metal- lurgical Company have deposited zinc and tin, or a mixture of both ELECTROLYTIC ZINC AS A PRINTING SURFACE. 347 metals, upon thin sheet steel for making " tin " canisters or boxes, by which a printing surface is produced which receives the ink with per- fect facility, the object of which is to save the cost of separate labels and the trouble of pasting them on the boxes, while at the same time the printing is more lasting than in ordinary printed labels, which are liable to be torn off. After the sheet steel has been coated with zinc, and printed upon in the flat, the metal is formed into shape as usual, and a final coating of lacquer renders the surface brilliant and effective. Hermann's Zinc Process. By this process, which was patented in Germany 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. THERE 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. ELECTBO-DEPOSITION 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 may be 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 VAEIOUS 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 maybe 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 Eahr. 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. 351 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 352 ELECTRO-DEPOSITION OF VARIOUS METALS. any desired quantity from this firm at the following rates : Rolled and cast cobalt anodes, i6s. 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, kupftrnickel, or ' false 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, the 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 hydra ted chloride of cobalt, from which various cobalt baths may be prepared according to the directions given below. Secquercfs 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. A A 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 reffia 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 current from two or three Smee cells. M. Bertrand advises a neutral solution 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 that 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 1-490. It is highly caustic. Gore says: "A similar solution may be prepared by the battery method. This consists in passing an electric current from several cells through pure and strong hydrochloric acid, by means of a large anode of antimony, until a good deposit is obtained upon a cathode of pla- tinum of equal surface. This solution is nearly colourless, almost free 356 ELECTRO-DEPOSITION OP VAEIOUS METALS. from iron, and much more pure than the former. A very good solution may also be easily made by saturating 10 ounces, by measure, of strong hydrochloric acid, with freshly precipitated teroxide of anti- mony (N.B., not that made by oxidising antimony by nitric acid, nor that which has been long exposed to the air), then add about 5 ounces more of the acid to the clear portion and stir the mixture." 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 ia 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. "An excellent solution," Gore further observes, "may also be made by dissolving an avoirdupois ounce of oxychloride of antimony in 5 ounces of pure hydrochloric acid of specific gravity 1-12. The acid chloride of antimony is an excellent conductor of electricity ; it dissolves the anode freely, yields plenty of bright reguline metal if the battery power is not too strong and its depositing power does not deteriorate by exposure to light or air. It is decomposed more or less readily by zinc, tin, lead, iron, brass, copper, and German silver, each of which coat themselves, with antimony in it, by simple immer- sion. Articles immersed in it require to be washed with hydrochloric acid before washing them with water, otherwise the latter decomposes the adhering film of liquid, and covers the article with a white in- soluble powder." 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 (potassic 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. " This mixture forms an excellent one for depositing anti- mony ; it is a good conductor of electricity ; it is not injured by long- DEPOSITION OP LEAD. 357 continued working, or exposure to light or the atmosphere. (I have deposited antimony from it constantly during many months.) It will bear a very strong current without the deposit being caused to pass into the state of a black powder ; it yields reguline metal rapidly, and in coatings of any desired thickness. (I have obtained deposits from it a quarter of an inch thick.) Deposits of about TJ of an inch in thickness may be obtained in about three days and three nights ; articles which are wet with this solution may be washed clean in water alone, with- out requiring to be previously washed with hydrochloric acid." Gore. 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 broivning 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. ELECTKO-DEPOSITION OF 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 metallo- chromy, as will be seen below. Metallo-Chromes. 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. 120. 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-CHROMES. 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. BecqmreVs 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 metallo- chromes is to place over the steel plate a piece of card, cut into some regular device, as shown in the illustration, and over this 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 metallo -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 ELECTKO-DEPOSITION OF VARIOUS METALS. Metallo- chromes 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. Believing that metallo-chromy may advantageously be applied to many useful purposes in the metal arts when applied to nickel-plated articles, the author deemed it advisable to patent the improvement. Deposition of Aluminum 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 [F] 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 f acility 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, 1855. 362 ELECTEO-DEPOSITION OF VAEIOUS METALS. mixed in a porcelain crucible, heated to about 392 Fahr. The com- bination is effected with disengagement of heat, and a liquid i>? 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). Thomas and Tillers 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. Jeancoii's Process (American) consists in depositing aluminium from a solution of a double salt of aluminium and potassium, of the specific gravity 1*161, 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, potassa, &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 Woolricli'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 VAEIOUS METALS. at a temperature of about 80 or 100 Eahr., 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 causes 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. G-oze reduced the metal silicium from a solution of monosilicate of potash, prepared by fusing one part of silica with *\ 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 Formula? 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 volatilisalle 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 ouly 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 maybe termed the direct tc ay ; 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. J. Take of Good sheet brass i ounce. Nitric acid (by measure) about . . .4 ounces. Water ... . 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 shall, 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 BRASSING 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, the 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 filtration as before should be again resorted to. Solution III. Acetate of copper 5 ounces. Sulphate of zinc 10 Caustic potash ' 4i lbs ' 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. It 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 dissolved in separate vessels : 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 i2 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, tho 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 PROCESSES. 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 uny 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 pound. 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 .1 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 be worked at a temperature of 150 Fahr., with a large brass anode, and a strong current. DE. HEEKEN'S PEOCESS. 373 Dr. Heeren's Process. According to tliis 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 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\ 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 1-036. 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 500 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 with 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^surf ace of the solution next the zinc or other dissolving plate is at a greater elevation than that of the external ior 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/livided 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 Napier) 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, * JSotryoidal, resembling a bunch of grapes ; referring to the nodular or knotty form which copper assumes at the back of electrotypes. ELECTKO-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 -01 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. Bacco'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, is next prepared, and this is added to the solution of BEASS SOLUTION FOR EOUGH 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 7 ounces. Cyanide of potassium 17 Carbonate of soda 34 ,,j 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 is 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 yj 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. zinc 2 soda ...... 4 37^ ELECTRO-DEPOSITION OF ALLOYS. Bisulphite of soda 4 ounces. Cyanide of potassium (pure) . . . . 4 Arsenious acid 2 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 good solu- tion," G-ore says, " for brassing by means of a separate current, with an anode of brass, may be made by dissolving 9 or 10 ounces of the strongest aqueous ammonia, 1 6 to 20 ounces of cyanide of potassium (with or without the addition of 20 of the strongest aqueous hydro- cyanic acid, ' Scheele's strength,') in 160 (i.e. i gallon) of water, and saturating the hot liquid with brass by means of an electric current ; it must be used at 212 Fahr." 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 XXVIII. 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-iron work 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 ELECTKODEPOSITION 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 : ELECTRO-BRASSING ZINC WORK. 381 Sulphuric acid i ounce. Hydrochloric acid 2 ounces. Water i 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 be 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 32 ELECTKO-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 Electro-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 OBSERVATIONS ON ELECTRO-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. If 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 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. Slack 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 is 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 J 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 : c c 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-eight 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-hairbrush, 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. Blorris 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 39 ELECTRO-DEPOSITION OF ALLOYS. liquid ammonia, 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 Fahr., 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 35,000 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, 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 is warm ; the object is now finished. NOTES ON ELECTKO-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 that 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 JBath. To keep up the strength of brassing baths, the plan suggested by the author 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 other of cast iron were placed in the bath simultaneously the former would at once become coated with brass, while the cast-iron article would 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 parts 394 ELECTRO-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 motion. CHAPTER XXIX. ELECTRO-METALLURGY. Application of the Term. Dechaud and Gaultier's Process. Electrolytic Eefining 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 Observati ons on the Electrolytic Refining of Copper. Gramme's Experiments with Sulphate of Copper Baths. Application of the Term. The term Electro-metallurgy, which, was applied by the late Alfred Smee 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 39 6 ELECTKO-METALLUKGY. the means of obtaining electric power. In the same year Mr. J. B. ElMngton 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 " 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, which we abridge from Mr. Williams 's able work, is as follows : Dechaud and Gaultier 'B 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 GAULTIER S PEOCESS. 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 G-aultier 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 39 8 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. Respecting 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 experiences 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 ELECTKOLYTIC 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.JF.) 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 at 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. 4OO ELECTRO-METALLURGY. 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 the amount of capital required for copper in stock. It must also be borne in mind that with the larger anode surface tanks of greater capacity 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. EUtington'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 --ffnd 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 12 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 whole series, the positive plates being at one end of the series DE. 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 |- 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. TV. 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. Mr. 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 rei'erring to page 26. 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 Daniell cell, having an E.M.F. of I Volt., resistance of -5 ohm., and connect with the same electrolysing cell. The current will be iVeber. 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 three 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 REFINING 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 : Galvanic Cell. Smee . Daniell . Bunsen . ro ro ro ro 2'0 2'0 2"O 2'0 9'5 0-5 g I! 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 s I I "00 I '00 roo I '00 roo I'OO i -oo i -oo I'OO I'OO I -00 I'OO I '00 9-23 9-23 9-23 18-46 18-46 18-46 18-46 36-92 36-92 36-92 36-92 9-01 9-01 9*01 9-01 9-01 18-03 18-03 18-03 18-03 36-06 36-06 36-06 36-06 II '1 9-01 18-03 27-04 36-06 90-15 18-03 36-06 72-12 180-30 36-06 72-12 144-24 360-60 0-5 ro ro ro 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. THENARD'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 2IO 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 15-588 II 2 00 7-995 332 14-652 IO 2 2O 9'535 362 13-620 9 2 40 "155 '394 12-546 8 3 00 I2'775 419 II-352 7 3 20 I4'535 '453 10-171 6 3 40 16-270 4 80 8-880 5 4 oo 18-040 500 7-500 4 4 20 19-990 '540 6-160 3 4 40 22'OOO 570 4-710 2 5 oo 24-140 "610 3-280 I 5 20 26*290 "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 ELECTKOMETALLUKGY. (in proportion of 1-210 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 same 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 3 2 -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." Dr. Kiliani's Observations on Electrolytic Refining of Cop- per. Dr. Martin Kiliani, of Munich, recently published a long paper DR. KILIANI ON THE ELECTKOLYTIC REFINING OF COPPER. 407 in the German Berg-und Huttenmdnnische 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 (erzeugf) 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 ELECTRO-METALLURGY. motive force) ; and that the metal will be first deposited from the 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 copper. If, therefore, but a small amount of sulphides is contained in the copper anode, the current will act only on the copper DE. KILIANI 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 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 net 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 remain 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 4IO ELECTRO- METALLUKGY. 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 vary 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 of 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 7-1 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 the first series of experiments the weight of the deposited copper did not 412 ELECTRO-METALLURGY. lapmrnnaj jmoq aad ptre .moq Jtad pins q;Bq jaj jnoq ja "N ' b M N CO '* b I ' 00 rOUIt^-w O >nvOlOrj-TJ-00 O in t^ in ro TJ-VO -" co >n o in w oo w Vj- t^ O 01 CO CO V~> M N CO CO HI 8OO NVO OVO O O rj-vO O ^ O HI O lO gococooocoooooovo O COOO OVOCOt>OCTiNOt^ w COM in 8OOOOOOOOOOQCO O O >n 5 O O O p l>vp p J> 'HI COOO in 'rf CTlOO '<-< N "m O> CO t> wvo Minovo O>HI t^ N cooo m cooo vo N o\co m co o o> t~oo rt in in cooo < in V invb t>.vb invb vb m co dob b b b b b b b b I I notjOB in pnibt| aq^ jo" aoiqj p o\oo vp oo vp oo ri-vp w vp : w b^i b "c\ b^i "N N w Vo rh Vo i P CTiOO p p p C< 00 OO 00 O CO t^ o\ 'o\ o\ o\ o\ N N b 'M Vo Vo V V in ino omo ininom b b 'vTioo do i>- t^vb vb vb in V w M N o rf n nvb r>oo oo oo W covo cy> N oo s^uaomad N ro TJ- mo j>oo cr> o 12 and due to n ad bee achine xperiments N temerat se experiment stance of the etres long. in he r No. he ft r- M ^TJ 3*8 ^.ng fjftrtl C--H> S a> fl Sg S | ll~ll :al|a s A". B lAi nTb >> . 6 s'S'S * gSfc ssIsS !^ s t 5.2 b o M ^ o a .;siii 5l^ 2 |iis! ^ fr" 5 1 8 2 2 a ^ -lit I^ifli ^JS'g. H .sS'i T a.!-" 3 c ills* IS31J5 gflsl k o ^ rt 5^5 Big-SB ss- 5|| I GRAMME S EXPEEIMENTS. 413 japuiBiuaj ' aq^jo aj inoq auo m I'B^oj, '"too b Tt- s. in o rf co o ci oo en co vp in in in in in jo SUISTJ aq^ ^q paqjosqy uojiouj: ^q paqao'sqy -jno aq^ TBUIJ uorpt? UT pmbn saxjarat^uao a-renbs m q;^ qo^ajo in o> M O O^ t> w b b "t ro O\ N O>VO VO vo O\ b b b w in r> co oo M VO CO M OO t^- OOO VO t^ CO Tf in W -rf o-) rr M M n b b b b b CO co TJ- m so -aj aq^ jo VO VO Tj-VO W p >p VO M in V>. in Jnoq 9UO Ul IB10J, jo Suisu aq^ Iq paqjcosqy ^q pa'qjosqy anp asrjj m spinbij " ' laqumjsj s^uarauad CO O p co p vp l> in rf run CJ rf w CO VO O IH 00 b b "w b ^- co co * in Tj- o v> W O Tj- M o moo vo vo t^do o> m N N b b "o b in M vo o^ CO N M VO VO 00 00 N vb b> N en M mi> m o o MOO do in M 414 ELECTRO-METALLURGY. exceed i'g6 gramme. The practical fact to be deduced from these experiments is that when dynamo -electric machines are employed considerable economy is effected by joining the baths in series. Third Series. In this series of experiments Gramme determined to maintain constant the intensity of the current in a series of compara- tive trials, which induced him to increase the surface of the anodes and cathodes, as also the number of baths united in series, so as to maintain constant the total resistance of the circuit. In Table 2 it will be seen that the quantity of copper deposited in a bath is about the same in all the experiments. The speed of the machine and electro -motive force did not vary, and the work expended remained practically invariable. "These experiments," says M. Fontaine, "are in perfect accord- ance with all the known theoretical notions except on one point ; it will be at once observed that M. Gramme was driven to increase the sections of the liquid in a greater ratio than the number of baths joined in tension. However this may be, various circuits are seen here, with uniform resistance and invariable electro -motive force and intensity of current ; it is therefore not surprising to see that in each part of these various circuits the quantity of deposited copper practi- cally remains constant. But it will be observed that the total quantity of copper deposited in the complete circuit is proportional to the number of baths ; from which it might be concluded that with a fixed expenditure of work it is possible by means of suitable arrange- ments to almost indefinitely increase the total deposition." Fourth Series. In these experiments M. Gramme substituted in- soluble lead anodes for the copper anodes in the sulphate of copper baths, and found, as was to be expected, that the polarisation was considerable, while the deposition of copper was much less than before, owing, of course, to the lead anodes not keeping up the strength of the bath. M. Gramme thus sums up the results of his experiments : " I have placed myself in conditions which I believe to be favourable for the measurement of the work expended in each experiment ; the constancy of the work was nearly perfect during the three hours which each experiment lasted ; I constantly verified it by galvano- metric observations. At the termination of the experiment I opened the circuit and placed a Prony. brake on one of the fly-wheels of the gas-engine, bringing it back to the speed at which it ran during the electrolytic operation, and I concluded from it what had been the expenditure of work. I could easily afterwards, by disconnecting the gas-engine from the dynamo, ascertain what proportion of the motive-power was absorbed by the passive resistances of the latter. This quantity is given in the above three tables. I wished to go further and ascertain the loss of work corresponding to the heat- GBAMME S EXPERIMENTS. 415 ing of the baths, and have arrived at the results by the following means : ' ' In every experiment I took both the initial and final temperature of the baths ; an inactive bath placed near at hand served as a means of comparison. The difference between the final temperature of the active baths and of the inactive one represented the rise of tempera- ture due to the current. Taking into account this difference, as also the quantity of the liquid operated upon, and the specific heat of the liquor, which I have found equal to o - 8o, I obtained the number of calorics supplied to the baths by the passage of the current ; multi- plying them by the mechanical equivalent of heat, I obtained the quantity of work represented by this apparent heat. It will be understood that it is only the apparent and sensible heat of which I have thus been able to calculate the value ; and that the results which I have obtained are inferior to the real figures. Deducting from the total work performed by the motor in each experiment the work corresponding to the friction of the electric machine and to the heat- ing of the liquids, I obtained the quantity which I call remainder in the columns of my tables. In the experiments of the third series (Table No. 2), we have the irrefutable proof of the fact that the expenditure of work with soluble anodes in electrolysis can be taken as nil ; for the deposition is seen to pass from 15 to 60 grammes, without giving rise to an increase of work which could be measured. If the experiments of Table No. i show everywhere a remainder of work, the use of which cannot be precisely determined, it must be observed that this remainder grows smaller as I realise some better conditions, and becomes as low as '868 kilogrammetres, and so less than one -sixth of the total work. It is explained by calorific work in the other parts of the circuit." The foregoing exhaustive experiments, conducted as they un- doubtedly were with the utmost precision and care, not only confirm accepted theories, but also support the view that with a definite amount of current the deposit of copper may be increased almost ad infinitum by increasing the number of the baths in series an impor- tant consideration in districts where fuel is dear and the cost of elec- tricity proportionately high. CHAPTER XXX. ELECTED -METALLURGY (continued) . Progress of Electrolytic Copper Refining. Copper Refining at Hamburg Copper Refining at Biache. Copper Refining at Marseilles. Electro- lytic Refining at Oker. Electrolytic Refining at Birmingham. Electro- lytic Refining in America. Electrolytic Treatment of Copper in Genoa. Cost of Electrolytic Refining. Arrangement of the Baths for Elec- trolytic Refining. Progress of Electrolytic Copper Refining. It is now about twenty years since the first practical development of the electrolytic method of refining- copper was established by Mr. J. B. Elkington, with the aid of Mr. Henry Wilde's magneto -electric machines, and for many years the procese was exclusively practised by this firm. Since that period, however, the method has been very extensively adopted, not only in this country, but on the Continent, more especially in Germany, Saxony, and France. The North German Refining Works at Hamburg have adopted the electrolytic method for upwards of ten years, the machines of M. Gramme being used. More recently it has been practised at the Oker Foundry, near the mines of Mansf eldt, Germany, with Siemens' large machines ; by MM. Oeschger and Mesdach, at Biache (Gramme machines) ; by M. Hilarion Boux, at Marseilles, (Gramme) ; by MM. Lyon-Allemand, at Paris, and by M. Andre, at Frankfort (Gramme) ; by the Mansfeldt Mining Company, at Eisleben, and by Messrs. Sterne & Co., at Oker (Wilde's machines). Besides Messrs. Elkington's extensive works at Pembrey, South Wales, where Wilde's large machines are employed, the electrolytic refining process is carried on by Sir Hussey Vivian at Swansea (Elmore's machines) ; by Mr. W. A. Hills at Chester (Wilde's machines) ; by Messrs. Wil- liams, Foster, & Co. at Swansea (Elmore's machines) ; Messrs. Charles Lambert & Co. (Gulcher machine) ; and by the Elliott Metal Refining Company at Selly Oak, near Birmingham, where Wilde's machines are employed. It will thus be seen that the electrolytic method of copper refining is gradually but surely making considerable progress ; indeed, the important improvements which have been made in dynamo - electric machines during the past three or four years have greatly influenced this result. From information which has been conveyed to us, we have no doubt that in a very short period the art of electro- metallurgy will attain a far greater extent of development, both at PROGKESS OF ELECTROLYTIC COPPER REFINING. 417 home and abroad ; and to this end manufacturers of dynamo -electric machines are devoting much attention to the construction of machines specially suited to electrolytic copper refining 1 . As we have before remarked, there is much difficulty in obtaining information as to the precise methods adopted at the various electro- lytic refining works, nevertheless certain points of detail concerning the general system adopted at the respective establishments gradually find their way to the public by some occult means, as is usually the fate of all secret processes sooner or later. The following particulars concerning the principal refineries will give the reader a general idea of the special features of each system of working, and guide his judg- ment as to which is the most effective and economical. It must not be forgotten, however, that where water-power is not available for driving dynamo machines, the cost of fuel in the various districts is greatly different, often in the proportion of one to four. Besides this, the coppers refined at the various works differ considerably in the nature and proportions of their impurities, by which their conducting- power as anodes is greatly influenced, and the cost of electricity increased or lessened accordingly. Copper Refining at Hamburg. The North German Refinery is under the control of Dr. Wohlwill, who has made the electro-metal- lurgy of copper his special study. To carry out his system at the above works, six large No. I Gramme machines are employed, besides which a still more powerful machine, constructed under his own direction, is used. The principal features of Dr. WohlwilPs method consist in keeping the various baths at a uniform strength, and always at the same temperature ; the machines are made to revolve at regular speeds, and are kept in perfect order ; all the coppers to be treated are subjected to analysis both before and after the electrolysis. It is by thus keeping all things equal that he is enabled to produce copper of very fine quality. The first Gramme machine constructed for Dr. Wohlwill for the chief electrolytic installation at the North German Hennery is pro- vided with two collectors and four brushes ; each collector has twenty sections. The spirals of the bobbins are each composed of seven strips of copper 10 millimetres (0-4 inch) wide and 3 millimetres (or about % inch) in thickness. Forty groups of copper ribbon correspond to the forty sections of the two collectors, so that each spiral is composed of two identical half spires juxtaposed, and soldered at their extremities to a radiating piece which connects them to one of the sections of the double collector. The inducted ring is therefore composed of forty partial bobbins, of which twenty are connected to the right-hand side, and a corresponding number to the left-hand side collector. The total resistance of the induced bobbin is -0004 ohm ; when the two parts E E 418 ELECTRO-METALLURGY. are joined in parallel this resistance is reduced to -oooi ohm. The E.M.F., with a speed of 500 revolutions per minute ; is equal to 8 volts for the coupling in series, and to 4 volts for the coupling in parallel. The eight electro-magnets of this machine have iron cores 1 20 millimetres (or 4f inches) in diameter, and 410 millimetres (16*5 inches) in length. On these cores are wound thirty -two turns of sheet copper, corre- sponding in width to the length of the electro, and I I millimetre in thickness. The resistance of the eight conductors in one single circuit is '00142 ohm ; when the electros are joined in two series their resist- ance becomes '00038 ohm. The total resistance of the machine is therefore -00038 ohm in quantity and '00182 ohm in tension. The total weight of copper is 1,620 pounds, and that of the entire machine about 49 cwt. The normal output of current of this machine is said to be 3,000 amperes for 4 volts, and 1,500 amperes for 8 volts electro- motive force. At the North German works there are forty baths arranged in two series of twenty ; the anode surface in each bath is nearly 325 square feet, giving a total of 13,000 square feet of surface for the whole of the baths. The anodes and cathodes, or receiving plates, are arranged at about 2 inches apart. The copper is deposited on the cathodes to the thickness of about % inch, and at the rate of about 64 pounds per hour, in all the baths, or 1,760 pounds per day of twenty-four hours. The motive power absorbed is about 16 horse-power, giving a produc- tion of I pound of pure copper with the consumption of 0-4 horse- power per hour. At the same works two other series of baths are employed, the number of which is 120, and these are connected in succession. Each bath is furnished with anodes exposing about 160 square feet of surface, and the entire series of 120 baths has a resistance of O'l ohm. The current for these baths is obtained from two No. I Gramme machines, connected together in series of 300 amperes, with an electro -motive force of 27 volts. The amount of copper deposited per day of twenty-four hours is 2,000 pounds, at an expenditure of 12 horse-power, or say - horse-power per pound of copper per hour. The nature of the electrolyte employed at these works appears to be a secret. It has been affirmed that nitrates are used. The cost of fuel being an important consideration at Hamburg, Dr. Wohlwill has specially designed his baths to economise motive power as far as possible. After an extensive series of practical trials, he found that considerable advantage was obtained by working with large cathode surfaces, and allowing only thin deposits to take place upon them. In his first installation the rate of deposit is only about 0-005 pound per square foot per hour, or only 0-00012 inch per hour in thickness ; in the other installations referred to, the deposit is still further reduced, with, as will be seen, a considerable reduction in the COPPER REFINING AT MARSEILLES. 419 expenditure of motive power. The value of copper under treatment in one of the installations at Hamburg is said to be equal to about ,8,000. Copper Refining at Biache. Messrs. CEschger, Mesdach, & Co., of Biache-Saint-Waast, near the English Channel, have an installation in which a large Gramme machine, similar to that constructed for Dr. "Wohlwill for the Hamburg works, is employed. Twenty baths are used, from which the daily production of copper is about 800 pounds. The baths are each about 10 feet long, 2 feet 6 inches wide, and 3 feet deep, and are constructed of wood nearly 3 inches thick, and lined with lead. These vats are coupled in series, and are charged with a solution of sulphate of copper maintained at a density of 19 Baume. Each bath is furnished with 88 anodes and 69 cathodes of equal total surfaces ; the anodes, which are 28 inches long, 6 inches wide, and |- inch thick, are arranged in 22 rows of 4. The cathodes, which are 34 inches long, 7 inches wide, and about -fa inch thick, are placed in 23 rows of 3. The total surface under action represents, therefore, about 10,800 square feet. The copper is deposited upon the cathodes of sufficient thickness to be taken directly to the rolling-mill. The production of copper at these works is about 1,540 pounds per day of twenty-four hours, the thickness of the deposit being equal to about 00012 inch per hour. The silver and gold (if any) are deposited in the " mud " at the bottom of the baths, and this is removed from time to time and washed, and after being dried is fused with litharge or with a reducing agent, the product in the former case being treated as argentiferous lead. "When the electrolyte becomes heavily charged with iron and other impurities, it is evaporated and allowed to crys- tallise. Copper Refining at Marseilles. M. Hilarion Roux has an instal- lation at his refinery in Marseilles, in which a No. I Gramme machine is employed. There are 40 baths, having a total anode surface of about 10,000 square feet, or about 250 square feet for each bath. There are 115 plates in each vat, each being 2 feet 3 inches long, 6 inches wide, and ^ - inch in thickness. Each plate weighs about 26 pounds. The plates are immersed about five-sixths of their length, the anodes and cathodes being placed at a distance of about 2 inches from each other. The total weight of copper under treatment is 54 tons, of which 23 pounds are refined per hour, or about 550 pounds per day, with an expenditure of 530 pounds of coal per day for driving the Gramme machine, which revolves at a speed of 850 revolutions, and absorbs about 5 horse -power. The bath is worked at a density of 16 to 18 Baume,* and is maintained at a temperature of 25 C. (77 * Or about 18-267 per cent, of sulphate of copper. 42 O ELECTRO-METALLURGY. Fahr.), the deposit being at the rate of 70,002 pounds per square foot of cathode. Electrolytic Refining at Oker. At these works, five large Ci dynamo -electric machines furnished by Messrs. Siemens and Halske, of Berlin, are employed, one of which has been at work for upwards of four years. The machines have been constructed to give low internal resistance and great power in amperes, which has been effected by surrounding the soft iron and the bars of the electro- magnets with copper bars of rectangular section, instead of winding them with wire as in electric -light machines. The induced bobbin is provided with a series of bars with the Hefner -Alteneck system of winding; the corresponding bars are joined together by means of large spiral bands, placed on the face of the bobbin, opposite the collector. On the anterior face of the bobbin, on the collector side, the bars are connected to the latter by means of strong copper angle pieces. The inductor also consists of a single layer of copper bands coiled by series of seven on each branch, or twenty -eight in all. The bars are insulated by means of asbestos, which being a non-con- ductor, allows the machine to become heated without doing harm. Each machine works twelve large vats, and is driven, we understand, by water-power of from four to five horse-power, and deposits I kilo- gramme (2-2 Ibs.) of copper per hour, or about 300 kilogrammes (6 cwt.) per day. Electrolytic Refining at Birmingham. The Elliott Metal Eefin- ing Company, of Selly Oak, near Birmingham, employ five large "Wilde machines, which refine about ten tons of copper per week. The vats are arranged in five series of forty- eight in each, one Wilde machine being employed for each group of forty-eight baths. The vats are 2 feet 9 inches long, by the same width, and are 4 feet deep ; each vat contains 16 anodes, which are each 2 feet long by 6 inches wide, and J inch thick, and weigh 26 pounds. There are only ten cathodes in each vat, each cathode being i foot 4 inches long, 22 inches wide, and '03 inch in thickness, and weighing 2-86 pounds. The total weight of copper per bath is about 450 pounds, and in a series of forty-eight baths about ten tons. The anodes and cathodes are arranged at about 3^ inches apart. The anodes are immersed only to the extent of 20 inches of their length, so that the surface under action, including both surfaces of the anode, is only if square feet, or 30 square feet in each bath. The yield of copper for the forty-eight baths approximates 30 pounds per hour, or about '65 pound per bath per hour, which corresponds to a current of 235 amperes. The anodes are replaced every five weeks, and the operation progresses for 156 consecutive hours per week. The temperature of the electrolytic department is uniformly maintained at 68 F.), and the density of the ELECTROLYTIC TREATMENT OF COPPEE IN GENOA. 421 "bath kept up to 16 B. The particulars concerning the improved Wilde machine adopted at these works are given in Chapter II. Electrolytic Refining in America. It is stated that the Balbach Kenning Works in Newark, N.J., are probably the largest in the world, the daily production of copper being about sir tons. The current is obtained from four dynamos, furnished by the Excelsior Electric Company, of Brooklyn, New York. Each of the dynamos is driven by an independent Westinghouse engine. The three larger dynamos produce a current of 30,000 watts each, while the fourth is a smaller machine of 15,000 watts capacity, which was put down for the firm about two years and a half ago, to enable them to ascertain whether the electrolytic method of refining was remunerative before embarking in the business upon a large scale. The work goes on day and night, with a short intermission each day for cleaning and oiling the engines and dynamos. The foundry for casting the anodes, the mechanical appliances for handling and transporting them and the finished plates, are all designed with the object of saving manual labour as far as possible. There is another large establishment in the States for the production of electrolytic copper and the separation of the precious metals, namely the St. Louis (Mo.) Smelting and Refining Company. Besides the two principal works above referred to, there are some other less important works, and the great interest taken in the results obtained shows that electro-metallurgy is making rapid strides on the other side of the Atlantic, where, of all places in the world, a successful process is sure to command attention, and when once taken in hand, pushed forward until it acquires the highest state of development that enterprise and a due appreciation of the advantages of labour-saving machinery can bestow upon it. Electrolytic Treatment of Copper in Genoa. A somewhat recent addition to the list of firms adopting the electrolytic treatment of copper is the Italian Mining and Electro -metallurgical Company of Genoa, whose works are at Casarza, but the system adopted differs considerably from that pursued by most other firms. The process may be thus briefly described : A portion of the ore is melted to a crude metal, or matte, consisting of copper, 34-7 ; iron, 38-6 ; sul- phur, 25 '3, as given by a representative analysis. Another portion of the ore is roasted and lixiviated, to obtain a solution containing as much sulphate of copper as is required to render the ferrous sulphate of the anode available for the electrolysis of the copper salt. The anodes are formed of the matte obtained after the fusion of the mineral, being cast in iron moulds into plates 32 inches square by i^ inch thick. The melting is effected in a small furnace fed by a fan, 15 tons of ore being operated upon in twenty-four hours, yielding 50 plates weighing 176 pounds each ; bands of copper are cast into the plates 422 ELECTRO-METALLURGY. for connecting with the source of electricity. To prevent these bands from being acted upon by the solution, the liquid is kept about f inch below the upper edge of the plates. The residues from the anodes, after the extraction of the sulphur, are returned to the furnace. The cathodes consist of thin plates of red copper, 28 inches square by -% inch in thickness, supported by a wooden frame. Upon these plates the copper is allowed to deposit to the thickness of \ inch. Dr. Higgs, from whose paper in the Engineer we obtained the above extract, says that, "by employing anodes of iron, copper, sulphur, such as ordinarily result from the first melting, the copper may be removed from the solution with an electrical efficiency comprised between 50 per cent, when there is no copper in the anodes, and of loo per cent, where, on the contrary, there is no iron. With the use of metallic sulphides in the anodes, all the sulphur contained in the mattes may be regained in a metalloidal state. The deposit is of good quality as long as the baths contain in solution about o-i per cent, of copper. After exhaustion of the copper, the solution contains basic persulphate of iron, protosulphate of iron, and sulphuric acid." The electrolyte, or sulphate of copper, bath is obtained by roasting very rich ores and mattes in a reverberatory furnace, the roasting being so conducted as to yield more oxides than sulphides ; oxide of iron not being soluble in dilute sulphuric acid very little sulphate forms in the solution. The electrolyte is kept up to a normal strength of copper (about 4 per cent.) by circulation over roasted minerals. When the bath from excess of iron yields a pulverulent deposit of copper, with evolution of hydrogen, it is renewed. The baths are 6 feet 9 inches long, 3 feet wide, and 40 inches deep, made from wood and lined with lead. About twelve of these baths are required to yield 2 cwt. of copper per day, for which twenty dynamo machines, arranged in two groups of ten each, are employed, and each machine is connected with twelve baths arranged in chain. The dynamos yield a current of 250 amperes at 15 volts, and each bath is furnished with fifteen anodes and sixteen cathodes arranged two inches apart. The motive power is obtained from turbines. Cost of Electrolytic Copper Refining. When it is borne in mind that the electrolytic method of refining copper is pursued at the various works under totally different conditions, and that it is evidently not to the advantage of the respective competitors to make publicly known the special means by which they secure economy in the cost of their production, it will be at once seen that any published data in this connection must be received with caution. It is true that the capabilities of the leading dynamo -electric machines are well known, and that a given current will do a certain amount of work ; the coppers operated upon at different refineries, however, vary consider- COST OF ELECTROLYTIC COPPER REFINING. 423 ably in the nature and extent of their impurities, -which of course influences their conductivity ; again, the systems of working- are different, some employing larger anode and cathode surface than others, while, again, the condition and strength of the electrolytic is varied according to the judgment and experience of each electro- metallurgist, according to the particular metal which he has to treat. That electrolytic copper refining has proved to be a profitable method of obtaining pure copper in large quantities at several large works may be considered as proved, by the fact that the process has been carried on without intermission for a great number of years. To arrive at an approximation of the cost of electrolytic refining of copper, it will be necessary to refer to Mr. Sprague's experiments on the deposition of copper which were conducted with a bath composed of saturated solution of sulphate of copper, 3 parts ; sulphuric acid, 10 parts, diluted with ten times its volume of water. The source of electricity employed was a Daniell cell, and the current was varied by varying the resistances, so that a given thickness (-0035 inch) was obtained in thirty hours as the slowest, and forty-five minutes as the quickest rate. Between a thickness of -00012 inch determined by repeated weighings and -00144 inch deposit per hour, the deposits were good, up to the limit of the last ; beyond this all quicker rates yielded defective deposits. Mr. Sprague concluded from these results, that the limit of current of I ampere to 33 centimetres, or about 5 square inches, could not be exceeded with advantage. This rate, from one to twelve, corresponds to 300 amperes per square metre, or nearly 30 amperes per square foot of anode. These results, however, would not be obtained in practice from the causes previously indi- cated (impure anodes, &c.) ; indeed, even under the most favourable conditions and with pure anodes, the deposit of copper in elec- trotyping seldom exceeds one-third of this rate. The following table shows the thickness of deposit obtained in a working week of 156 hours, including the results obtained by Mr. Sprague and M. Gramme. Inches. Maximum deposit (chemically pure anodes) . -067 Sprague's results (good deposits) ... -02 to -24 Gramme's results -0036 to -025 Hamburg Works l' 2 (.'006 Biache Refinery -02 Marseilles Works -007 Selly Oak Works, Birmingham . . . -06 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 baths 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 COPPEK 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. frs. 388-80 196-05 36r45 Hilarion Roux, Mar- seilles frs. 78-80 64-65 35'95 frs. 112*00 39'50 180-06 frs. 18 12 30 frs. 72-00 40- o 57'75 frs. I08'OO 40-00 5775 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 (53.) per ton at the works, we find that the motive power still costs i'2O 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 ELECTIKXMETALLUKGY, of Keith and others clearly indicate that in this direction is to be found the chief element of economy in electrolytic refining 1 , 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. Wohlwill's 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, 5s. 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 6| 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 AERANGEMENT OF BATHS FOE ELECTROLYTIC REFINING. 427 practical electrotypists will readily acknowledge. In telegraphy, pure electrolytic copper presents advantages from its nigh 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 1 2 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 scries 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 E resistance in ohms, the expression for weight of lead deposited per hour, applicable under the assumption above mentioned, is Pb= =* Ibs. per hour. 117 R x 117 CHAPTER XXXI. ELECTED -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. Letrange's Process. Luckow's Zinc Process. Electrolytic Treatment of Sulphides. MM. Bias and Meist's Process. Werdermann's Process. Electrolytic Refining of Lead. Keith's Process. Professor Keith, of New York, in 1878, devised a process for the electrolytic refining of impure lead, with the object of extracting the silver and at the same time separating the lead in a pure metallic state. The process, so far as the arrangements of the baths and the disposition of the anodes and cathodes, is the same as in Elkington's copper-refining process. In base bullion the chief constituent is lead, which forms at least 90 per cent, of the mass. To separate this from the silver, anti- mony, arsenic, &c., by electricity, many electrolytes were tried, in- cluding nitrate of lead ; but since the nitric acid set free would also dissolve the silver from the bullion anodes, this was not found to be a suitable electrolyte ; sulphuric acid, which dissolves lead in small quantity, but the sulphate of lead formed became precipitated in the solution, while no metallic lead was deposited upon the cathode. After having tried all the known salts of lead in varying combinations, Professor Keith finally obtained several solutions which would serve as more or less perfect electrolytes for lead, and it was to his success in this direction that the apparent practicability of his processes was due.* The electrolyte which he found most successful, and which was accepted as the best for the electrolytic treatment of lead, consisted of acetate of soda, about ij pounds to the gallon, in which 2^to 3 ounces of sulphate of lead were dissolved. The bullion-plates or anodes were thinner than those used in electrolytic copper refining, being only from th to i^ths of an inch in thickness. A plate of bullion 15 by 24 inches of this thickness weighs about 20 pounds. Before being put into the vats a muslin bag is drawn over each bullion -plate, the object being to prevent the residues (silver, &c.) from falling to the bottom * This process was carried on by the Electro Metal Refining Company, New York, but has since been discontinued. ELECTROLYTIC REFINING OF LEAD. 429 of the vat. The lead is intended to accumulate on the bottom of the vats, and by the above arrangements the impurities are prevented from mixing with the deposited metal. The muslin employed to enclose the anodes is fine enough to prevent the fine particles of residue from being washed through by agitation of the solution, while the liquid is freely diffused between the inside and outside of the bags, and the resistance not perceptibly increased. The diffusion of the liquid by agitation is absolutely necessary, since the lead becomes dissolved as sulphate by electrolysis, and this sulphate must diffuse itself in the liquid to replace the sulphate decomposed at the cathode to deposit metallic lead. If the diffusion were to take place too slowly, in a short time the amount of lead present in the solution outside the bags would be too little to satisfy the depositing power of the current, and hydrogen would be evolved, followed by polarisation. If the solution be constantly agitated, therefore, a much stronger current may be employed without danger of polarisation. Heating the solution also favours the diffusion, while at the same time it materially reduces the resistance ; it is, therefore, usually heated to about 1 00 Fahr. On working the solution it is maintained in a neutral state ; if allowed to become alkaline, the alkali (in this case soda) becomes decomposed, furnishing oxygen to the anode and per- oxidising the lead thereon, while hydrogen is evolved at the cathode and produces polarisation, irrespective of the diffusion of the solution. In working the above solution there is no polarisation, provided the liquid is kept in a normal condition ; the lead is dissolved from the anodes, and an exact equivalent of metal is deposited on the cathodes, and gathers as a crystalline coherent layer. In some cases, after the layer becomes sufficiently thick, it rolls off the surface of the cathodes and falls to the bottom of the vat ; sometimes, however, the cathodes require to be gently scraped to remove the deposited metal. When the lead is all electrolysed from the bullion-plates (anodes), the impurities alone remain in the bags, and these usually constitute about 5 per cent, of the whole mass . If the bag containing the anode be carefully removed, it will be found that the anode has changed but little in appearance ; it has a bright metallic aspect with a display of iridescent colour, and appears as if it had undergone no action ; if the plate be touched, however, it yields to the finger like blue clay, to which it bears some resemblance. This is the residuum, in which may be seen here and there small fragments of lead which had become detached from the anode as it grew thinner. The residuum is immersed in water, when the scraps are washed from the "mud," which then deposits in a clayey mass, leaving the water perfectly clear ; the scraps are after- wards remelted and recast into plates. The lead is drawn out from the vats at convenient intervals, and after washing to free it from the 430 ELECTRO-METALLURGY. solution which, attaches to it, it is dried quickly, and either pressed into "slugs," or otherwise melted at a low heat and cast into pigs. The residue, which contains the silver and gold besides the impurities, as arsenic, antimony, &c., is treated by a special process, which is thus described by Professor Keith : " In laying out our plan of procedure, we must first consider the conditions and liabilities. These may be formulated thus : "I. It is a wet powder, and must be dried. "2. The oxidisable constituents must be oxidised. "3. It must be mixed with fluxes and fused. "4. Antimony and arsenic are volatile, and carry off in vaporising, mechanically or otherwise, silver, and perhaps gold. It is absolutely necessary to get all the gold and silver, and as pure as possible, though they may be alloyed together. It is obvious that drying the powder and roasting it in a reverberatory furnace will cause a great loss in silver from volatilisation with arsenic and antimony, besides loss of powder carried off by the draught. Its roasting needs most careful treatment, as from the easy fusibility of antimony, masses of alloy may be formed which cannot be practically oxidised. Recognising these conditions and difficulties, the plan of proceeding is this : After having removed the powder from the filters while it is still wet, it is mixed with the proper quantity of nitrate of soda, when it may be dried without loss of dust, as the nitrate cements the whole together. When sufficiently dry it is placed in crucibles for fusion. These are cautiously heated : the nitrate decomposing gives oxygen to the anti- mony, arsenic, copper, iron, &c., thus forming teroxide of antimony, arsenious acid, and oxides of copper, iron, &c. The soda combines with the teroxide of antimony and the arsenious acids, forming anti- moniate of soda and arsenite of soda, which are fusible ; a little borax added makes the slag more liquid when the oxides of iron and copper are present. A button of pure gold and silver collects at the bottom of the crucible. Now, though antimony, arsenic, and arsenious acid are volatile, antimoniate of soda and arsenite of soda are not, so there can be no loss from their volatilisation. Nitrate of potash may be substituted for the soda salt with the same effect. This slag of anti- moniates and arsenites can be utilised in the following manner : When treated with hot water the arsenite of soda or potash is dissolved, and the antimoniate remains undissolved, together with the oxides of copper and iron. The arsenite of soda or potash is obtained by crys- tallisation, and finds its use in dyeing, colour -making, &c. ; or metallic arsenic may be obtained from it by sublimation. Antimony may be obtained from the residue by mixing it with charcoal and melting in a crucible. No copper or iron need be reduced with the antimony with proper care, but if they are, they may be removed by subsequent KEITHS LEAD IROCESS. 43! fusion with some teroxide of antimony. Perhaps it will not be found profitable to carry the utilisation farther than to save the antimony and arsenic." In this process the anode plates are cast thin, because the speed at which the electrolysis can be pushed is limited by the rate of diffusion of the sulphate of lead through the bags, as before explained. In practice it was found that with plates 15 by 24 inches, the rate of the electrolytic transfer of lead was from ij to 2 ounces of lead per hour, and a plate of this size, weighing 20 pounds, would therefore require from six to eight days. "With plates twice as thick, or of an inch, it would last twice as long, and to make a given return per day, the amount under treatment would require to be greater. Larger and thinner plates would be electrolysed more rapidly. The electrolyte does not become changed by continued use. Iron and zinc, if present in the bullion, become dissolved and remain in solution, but this does not impair its efficiency. A small quantity of sulphate of lead added to the bath will correct any defect from this cause ; moreover, the sul- phate of iron becomes gradually oxidised, and sesquioxide of iron rises to the surface, which may be skimmed off. The chief object in the treatment of lead base bullion is the separa- tion of the silver from the lead, which by the old or dry method is not only costly but imperfect, while the presence of antimony and other impurities greatly influences the facility of such treatment. In- deed, some varieties of bullion, containing antimony in large propor- tions, are so refractory that in many cases they cannot be separated with profit. By this process, however, the silver and lead are directly separated, whether antimony be present in the bullion in large or small quantities, while at the same time this metal is also saved, and can be sold at the market value. All the lead is recovered with the exception of a trifling percentage lost by vaporisation, oxidisation, &c., because the bullion is only heated sufficiently to be melted and cast into plates, instead of being repeatedly heated, as in the old pro- cess. Again, all the gold and silver are saved, while the lead is obtained in an almost perfectly pure state an important advantage in the electrolytic method of treatment. A sample of Keith's electrolytic lead was found on analysis to contain only -000068 per cent, of silver, or -02 ounce per ton, while only traces of antimony and arsenic could be detected, though a large quantity was used for analysis ; there was no copper, though there had been some in the bullion. The presence of the small quantity of silver was believed to be due to carelessly handling the bags covering the anodes, by which small particles of the residue washed out into the bath, and finally deposited with the lead at the bottom of the vat. The bullion from which this lead was elec- trolysed was also submitted to analysis, with the following result : 43- 9635 Of zLKJBli i~-:: i-il.-ss ::*-: iofceftlong.2 eoraedvi&p : -J-: n* a fr:~ lorn We wnds. Alt tibeiBteaf of wafkmif.i :.- :.^;.-;-5 ;: :_r V ZZITH'5 I-T-A~ FEC-rZ:::. 433 deposit was 360 pounds per day of twenty-four hours. It win be readily understood that the machine can be worked by night as wen asbyday. At this rate a plate would be exhausted in somewhat less than nine days. In practice the plates are not an erhannted, how, ever; there always remain small pieces which become detached from the rest of the plate. The weight of these scraps would average about I pound, though in this case many of the plates were cracked to begin with, and did not hold out wefl for tins reason. Borne, New York, which is tins described : " The works are in a one- storey building, 150 feet by 50 feet, of which the working capacity (three tons per day) requires only one- third the space. The castiag of tbabuffion-platesia done by means of a of mechanical moulds rotating sively under the spout of tho moulds, each holding at its upper part two thin strips of copper per- f orated with holes. Then the lead is poured into the mould it fills thesametime. At the side of the revolving system opposite from furnace, the plates are taken away by a boy, 1 strips and doses the mould again for; boy wffl make 180 plates per hour. Each plate is 24 by finch, and weighs 8 pounds. The plates are h and carried by an overhead railway to the vats. circular vats, made of a kind of concrete mixture. Each vat is 6 feet in diameter, 40 inches high, and has a central core or pfllar 2 feet in diameter, and equal in height to the vat. "The cathodes consist of thirteen circular hoops or bands of sheet brass, two feet high, and arranged concentrically two inches apart. The plates of bullion are lowered between these circular cathode*. The anode frame or bullion carrier has twelve consecutive rings of brass, 2 inches wide and inch thick, also arranged two inches apart. Bivet heads of copper project from these rings, and the buffion-plates are suspended to these by the eye-holes in the sus- pension hags. Each frame wffl receive 270 buUkm-plates, making- a total weight of bullion about 2,100 pounds per vat, or soghfly over one ton. The carrying power of the overhead railway is 3,000 pounds. The solution is allowed to overflow from the vats by a small gutter to tiie floor, which is of concrete, and grooved with gutters that lead to cisterns at the end of the building, which have a capacity off 3,000 gallons, whence it is pumped by a centrifugal pump to an overhead tank, where it is heated by a system of steam pipea to iooFahr., automatic electrical regulation of the temperature being secured bj a special device. Rom this tank the solution is distributed to the V* 434 ELECTRO-METALLURGY. vats by a system of pipes. An Edison dynamo -electric machine, constructed specially for this purpose, is used to furnish the cur- rent. This machine has an electromotive force of ten volts, and an internal resistance of '005 ohm, and produces the enormous volume of current of 2,000 amperes. This current will nevertheless be en- tirely safe to the employes on. account of its very low electromotive force. ' ' The vats are connected in series, and the power used by the machine does not exceed 10 horse-power for 30 vats. The vats are charged in rotation, three per day, and on the tenth day the first three are renewed, after which the renewal is kept up in the same order. In this way three tons are put under treatment every day, and three tons refined and returned. The anode carriers can be rotated around the core of the vat as a centre, and they carry mechanical fingers which scrape the surface of the cathodes by the motion. By remov- ing a plug, each vat may be rapidly emptied, and the crystalline lead shovelled out. This lead is washed in water and placed in a centri- fugal dryer, after which it is melted under oil or other reducing material, to expel the remaining traces of moisture without oxidation, and it is then ready for the market. In this establishment there are ovens and muffles, &c., for assay purposes and for reducing residues. These residues are washed in water, and the water run through a sieve to take out the scraps of bullion; they are then allowed to settle, after which the water is decanted and the residuum dried." Electrolytic Treatment of Ores. During the past forty years many attempts have been made to extract metals from their ores by elec- trolysis, and many ingenious processes have been devised, but few of these, so far as we are aware, have proved successful. Some of the earlier investigations of Bunsen, Sainte-Claire Deville, and Becquerel are of special importance as indicating the general principles upon which such electrolytic operations may be conducted ; there is little doubt, however, that much has yet to be done before the separation of metals from their ores will attain the position of a really practical branch of electro-chemistry. We have noticed in the case of copper refining by the wet way, that many attempts were made in this direc- tion long before a commercially successful application of the electro- lytic method was arrived at, and we still hope and believe that elec- tricity will yet be practically employed in extracting metals from their ores ; indeed some trials which we have recently made in this connection are at least of a very hopeful character. Becquerel's Process for Treating Gold, Silver, and Copper Ores. This process, discovered by the famous French chemist up- wards of thirty years ago, is based on the property possessed by BECQUEBEL'S PROCESS FOB TREATING GOLD OBES, ETC. 435 chloride of silver and sulphate of lead to dissolve in a saturated aqueous solution of chloride of sodium (common salt) and sulphate of copper. The chlorination of the silver by the wet way is applicable to ores in which the silver occurs either in the metallic state or as a simple sulphide ; when in the form of double sulphide, the dry method must be adopted. To chlorinate a silver ore, it is first reduced to an impalpable powder, upon which much of the success of the process depends. The substances employed for the chlorination are chlo- ride of sodium, sulphate of copper, or sulphate of peroxide of iron, the proportions depending on the composition of the ore and the percentage of silver present, ten per cent, of the chloride and twenty per cent, of sulphate being mixed with the pulverised ore. Copper exists in the ores either in the metallic state, in the form of oxide, or chloride, or as carbonate (malachite), sulphide (copper pyrites), &c. The sulphide is usually associated with sulphide of iron. When copper occurs in the metallic state, it is separated from the gangue, or earthy matter, by washing ; if in the state of oxide or carbonate, it is treated with sulphuric acid ; and when in the state of simple or double sulphide or a combination of sulphides, it is cautiously roasted, care being taken not to convert any portion of it into oxide. The copper pyrites being roasted by a sustained but not too high a heat, the sulphide of iron, which becomes reduced at a lower tempera- ture, is converted into peroxide, while the sulphide of copper changes into soluble and hydrous sulphate. The importance of careful roast- ing will therefore be at once apparent. Lead occurs chiefly in the form of sulphide, as galena, ; it is also found associated with silver (argentiferous galena), in which ores it is generally combined with sulphide of antimony, arsenic, &c. Galena is sulphated, as it is termed, by the dry method, by careful roasting, when sulphurous acid is liberated, the lead becoming oxidised and sulphate of lead formed. By the wet process, the sulphatation of galena is effected by causing a solution of sulphate of copper to react upon the plumbic sulphide by the aid of a solution of common salt. Having chlorinated or sulphated the silver, copper, and lead ores, solutions of the metallic compounds are made, salt water being used for silver and lead, and water for the copper salt. From these solu- tions, Becquerel deposited the respective metals by voltaic electricity, employing couples of zinc, iron, or lead connected by copper strips to tin plates or to fragments of carbon immersed in the solution bath. The oxidisable metals, however, were placed in porous cells filled with salt water. When adopting this " single cell " arrangement, he found that by grouping six baths together the chloride decomposed more ELECTRO-METALLURGY. rapidly without increasing the cost. In the first few hours three parts of the silver became extracted, but the remainder required a much longer period, owing to the conductivity of the bath being diminished, and consequently offering greater resistance to the current, which also decreased in strength. With dynamo -electricity, however, these difficulties of the process would be more readily overcome. In another arrangement, Becquerel employed a wooden case lined with lead, covered with wax, to hold the solution of sulphate of iron ; in this case there were two openings, one at the top for receiving the normal liquor, and another at the bottom through which the denser liquor escaped by a siphon. In the interior of the wooden case, leaded sheet-iron boxes were immersed, the end walls and bottom of which were of metal, and the lateral walls of open work lined with sheets of cardboard. Concentrated solution of sulphate of copper was allowed to enter at the bottom of these boxes, by means of siphons, while the weaker liquid was allowed to pour from the opening at the top. In one of these boxes the metal which was to receive the copper deposit was placed, and between each were cast-iron plates for generating the current. By this ingenious arrangement, a quantity of concentrated copper solution and weak iron liquor entered the boxes exactly propor- tionate to the weak copper liquor and strong iron liquor run out, which, occurring automatically, necessitated no personal attention, the only labour required being for the removal of the copper sheets when sufficiently thick, and replacing the iron plates when worn out. Becquerel thus sums up the advantages of his process: "From the facts set forth it evidently results that silver ores can be treated with- out difficulty by the electro -chemical process when sea salt is at a low price and there is enough wood in the locality for roasting the ore, if the chloridising cannot be done by the wet method ; that this process is particularly applicable to very complex ores, that is to say sul- phuretted ores ; and that although it is simpler than the Mexican or Freybergan amalgamation, there are, nevertheless, instances in which it will be preferred to this last method, which would not be suitable for the treatment of argentiferous galena and argentiferous copper pyrites. It is most probable that the electro -chemical method, by means of which silver, copper, and lead ores can be treated, will be adopted in practice when the principles upon which it rests shall have become familiar. It will more particularly be adopted in countries where mercury is only found with difficulty, and where wood is too scarce for treating the ore by melting, and where common salt is abundant." The above process was carried on by Becquerel for a considerable time at his works at Grevelle, many years before the introduction of dynamo -electric machines ; and although the process was not a com- LAMBERT'S PROCESS FOR TREATING GOLD AND SILVER ORES. 437 mercial success at that time there is much reason to believe that if practised in districts where fuel is cheaper than in France, and by the aid of dynamo -currents, far more satisfactory results could be obtained than were possible when /the great scientist pursued his ingenious method. Electrolytic Extraction of Copper from Ores Marcliese's Process. This process relates to the electrolytic treatment of copper ores, by which the inventor is " enabled to prevent the precipitation of iron or its compounds, and to obtain a very pure copper." For this purpose a portion of the ore to be treated is smelted into the con- dition of a matt, or regulus, consisting generally of copper, iron, and sulphur, which is cast into anodes. Another portion of the ore is roasted and lixiviated, sulphuric acid being added to dissolve out the oxides. The resulting liquid, chiefly sulphate of copper, with sulphate of iron, is transferred to the electrolytic baths, where it is decomposed by the current, metallic copper being deposited on the cathodes, while the sulphides of the anodes are dissolved, producing sulphuric acid and iron sulphates, so that none of the iron is deposited on the cathodes. To keep the liquor at the proper strength a consider- able portion of it is caused, by pumping or otherwise, to circulate from the baths to the lixiviating tanks, and after becoming enriched therein, to return to the baths. " A large part of the electric power necessary to decompose the sulphate of copper being generated by the oxidation of the iron in the anodes, very little extraneous electric power is required for the operation. The exhausted anodes are used for the production of sulphur and sulphuric acid, and the sulphate of iron contained in the spent liquor may be crystallised in the usual way. In cases where the liquor contains excess of iron a little granu- lated matt of copper is added to it. This is acted upon by the sul- phuric acid present, causing evolution of sulphuretted hydrogen and production of sulphate of copper ready for depositing." This reaction may be promoted by applying moderate heat. Lambert's Process for Treating Gold and , Silver Ores. The ore is dissolved by nascent chlorine, obtained by the decomposition of a soluble chloride by means of the current, by which the metals of the ore are converted into chlorides which become dissolved in the bath either as a consequence of their own solubility, or owing to the salts which enter into the composition of the bath. These chlorides are afterwards decomposed by electric action, and the metals deposited upon the cathodes. The three principal conditions necessary to the success of this process are : I. Polarisation at the anodes and cathodes must be avoided ; this is counteracted by keeping the mass of ore in motion, whereby the adhering gas is liberated. 2. The continuous col- lection of the deposits at the cathode prevents polarisation. 3. To ELECTRO-METALLURGY. secure a complete attack of the ore, all its parts must be subjected to the action of the nascent chlorine, which result is obtained by keep- ing the mass in constant motion, by which all its points are put in contact with the conductors of the current. The apparatus used by Mr. Lambert in his experiments consisted of a box divided into two compartments by a porous diaphragm. In one of these compartments was put the solution for receiving the cathode, which consisted of a strip of copper, which was cleaned and replaced at regular intervals. In the other compartment the ore was placed with a plate of carbon facing the cathode ; other plates of carbon were also placed in this compartment, so that the ore was surrounded by this conducting material. The stirring was effected by means of a current of water specially adapted for the purpose. Electro-chlorination of Gold Ores Cassel's Process. This process, which at the present time is being practically developed in London, possesses some features of interest, several of which are novel and ingenious ; it was devised and patented by Mr. H. R. Cassel, of America. In one trial of the process several tons of antimonial gold concentrates, which had been obtained from Queensland, were treated, and, according to the assay of Messrs. Johnson, Matthey, and Co., it showed that by this process 91 per cent, of the gold was extracted. The process, which is purely one of chlorination, is based upon the readiness with which chlorine in the nascent state that is, at the moment of its elimination from a compound attacks gold, in which state it has a far greater combining capacity than when generated by the ordinary chemical methods. The apparatus which has been most successfully employed consists of a large drum, within which are arranged a number of dense carbon rods ; these rods form the anodes, or positive electrodes, and are metallically connected with the positive pole of the dynamo, while the negative pole of the dynamo is con- nected with the hollow iron shaft of the drum, which serves both as axis to the drum and also a negative electrode of the apparatus. The shaft referred to terminates through stuffing-boxes in hollow standards or tanks, where finally the gold accumulates. In working the appa- ratus, which, as will be seen, is of an exceedingly simple nature, the drum is charged with about 2\ tons of ore, and salt and water added thereto ; it is then set in motion by suitable gearing, at a speed of about eight revolutions a minute. The current is then passed through, which decomposes the salt solution, and nascent chlorine and oxygen are evolved at the anode. As the drum revolves the ores are constantly brought in contact with the carbons, where both these elements are set free, and the metals become readily dissolved. Since the most refractory gold ores generally contain iron, which would naturally enter into solution with the gold, Mr. Cassel hit upon the idea of ELECTKO-METALLURGY OF ZINC. 439 adding caustic lime to the mixture of crushed ore and salt, which earth, by reason of its alkaline properties, at once combines with any hydrochloric acid as fast as it is formed, and effectually neutralises it, so that no iron can be taken up by the gold solution. At the same time a hypochlorite of lime is formed, which again, being decomposed by the water present, affords additional nascent chlorine for the gold ; the ultimate products of the reaction being chloride of sodium in excess, chloride of calcium, .terchloride of gold, and undecomposed gangue at the anode, and chloride of sodium and caustic soda at the cathode. In the iron shaft are bored a number of holes, and the shaft itself is covered with asbestos cloth, which, while preventing the gangue from entering the shaft, allows the dissolved gold to penetrate through the cloth. After the addition of the lime which precipitates all other dissolved metals present except the gold the latter metal is rapidly dissolved, and deposited by the electrical action in the interior of the pipe in a finely divided metallic state, and is carried thence into the hollow standards by means of an Archimedean screw fixed in the pipe. The standards are provided with movable doors, from which the gold "slime" is from time to time withdrawn, when, after drying, it is ready for melting. In the above process it will be seen that the presence of the lime not only checks the formation of iron salts, but instantly precipitates them when formed, as also all other metals which may be present in the auriferous pyrites. Electro-metallurgy of Zinc. Many attempts have been made to apply electricity to the extraction of zinc from its ores, and although these have not yet resulted in a commercial success, we believe that further perseverance in this direction will ultimately lead up to this. The enormous expense attending the ordinary methods of obtaining metallic zinc from its ores would render a successful electrolytic pro- cess specially valuable if the metal could be obtained pure by this means. The two principal ores from which zinc is at present obtained by the ordinary metallurgical processes are calamine, or native car- bonate of zinc, and blende (sulphide of zinc). These ores being in- soluble, they must be subjected to some process which will convert them into soluble salts before the electrolytic method of separation could be applied. For this purpose hydrochloric and nitric acids have been tried, but the process introduced by Letrange is, in the opinion of M. Hospitalier,* "the most practical, because it is the least expensive." Letrange's Process. The process is thus described: " Letrange transforms the insoluble blend into a soluble sulphate by a very simple * " Modern Applications of Electricity," by E. Hospitalier. Translated by Julius Maier, Ph.D. 44 ELECTRO-METALLURGY. process, in which the sulphuric acid necessary for the formation of the sulphate is supplied by the ore itself. It is well known that by the roasting 1 of the sulphur ores part of the sulphur forms a sulphate, whilst the remainder is given off in the form of sulphurous acid. This latter can be converted into sulphuric acid in the usual way, and the acid thus obtained can be used as a solvent for the ore. " The ore, consisting of a mixture of blende and calamine, is roasted at a moderately high temperature, so as to obtain the largest possible quantity of zinc sulphate. The sulphurous vapours, converted into sulphuric acid, are used either for the solution of the calamine or of the roasted ore. After the ore has been converted into sulphate it is placed in large tanks, and treated with water. The solution of zinc sulphate passes slowly into another series of tanks, when it is exposed to the action of the electric current. The liquid sulphate sinks slowly to the bottom of the tank, and the sulphuric acid liberated at the positive electrode gradually rises to the top, from whence it flows into another tank containing roasted calamine. A continuous reaction is thus established ; the liquid current first passes through the dissolving tanks, where the acid dissolves the zinc contained in the ore to exhaustion, then passes into the precipitating tanks, where it deposits the zinc, and changes back into acid, only to be again employed as a solvent. The same liquid, however, cannot be used ad infinitum, because the ores contain oxides lime, for instance which do not part with their acids by electrolysis. "The electrodes employed in this method are not identical, the negative electrode consisting of a thin plate of zinc, the positive electrode being formed of a leaden plate. On this latter the iron con- tained in the liquid is deposited in the form of oxide, which detaches itself and sinks to the bottom of the tank. As regards the lead, the silver, and the other metals insoluble in sulphuric acid, they remain in the residue, from which they can be extracted. The electric current necessary for these operations is supplied by the dynamo -electric machine, and Letrange uses, as much as possible, natural forces for driving them. In this latter case the operations are reduced to placing the roasted ore in the dissolving tanks, removing the residue, and re- placing the electrodes charged with deposited zinc by fresh plates. When a steam motor is required, the quantity of coal used for the production of 2 cwt. of zinc is the same as for I cwt. by the ordinary method. There is an enormous saving, too, in the original outlay, which for the ordinary method amounts to ,40,000 for the production of 20,000 tons of zine. The new process only requires, for the same production, from 200 to 300 horse-power, a corresponding number of dynamo -electric machines, and a certain number of dissolving tanks. The outlay in this would not exceed ,20,000." ELECTROLYTIC TREATMENT OF NATURAL SULPHIDES. 441 To simplify his process, Letrange causes the sulphurous acid to act directly upon the oxidised ore and the carbonate without previously converting it into sulphuric acid, by which he obtains sulphite of zinc instead of sulphate ; this salt, however, is as readily decomposed by the current, and, moreover, becomes gradually transformed into sulphate by the action of the air. This exceedingly ingenious and well-devised process certainly deserves the fullest attention, and if placed in the hands of experienced persons, possessing a thorough practical knowledge of electrolytic operations, there can be little doubt, we should think, as to its success. Much, however, will depend upon the arrangement of the baths, and the amount of anode and cathode surface employed, so as to diminish the resistance of the baths to the fullest extent attainable. The chief difficulty in the way, however, is in the electromotive force required for the decomposition of sulphate of zinc, which, if it exceeds 1-5 volt, involves the decom- position of water, and consequent loss of power. Iiuckow's Zinc Process. In this process zinc ore mixed with coke is used as the anode, and a zinc plate forms the cathode. A large rectangular bath is used for the operation. The mixture of ore and coke is placed in an openwork case, and a wooden frame weighted with lead and covered with a thick cloth is placed under the cathode to collect the precipitated zinc. During the electrolytic action froth is formed, which must be skimmed off as it occurs. When a solution of sulphate of zinc is employed, care must be taken to keep the solu- tion neutral ; although this is not so necessary when chloride of zinc is used, this latter solution has the disadvantage of disengaging chlorine at the anode, the fumes of which are exceedingly irritating to the lungs. Luckow recommends for the direct separation of zinc from blende a solution of sea salt slightly acidulated. Electrolytic Treatment of Natural Sulphides. There have been several attempts to treat native sulphides electrolytically, and indeed the subject is being followed up at the present moment in more than one quarter. It appears from the following communication* that M. Deligny turned his attention to the sulphides in 1881, for he then wrote to the journal mentioned below : " I started from this fact, that the various natural cupric sulphides, and their compounds or mixtures with iron pyrites, are tolerably good conductors of electri- city, and are more or less rapidly attacked by an acid in the presence of nascent oxygen. It was therefore to be expected that one of these compounds, taken as the positive electrode in any electrolytic action, should throw off, at least slowly, a certain portion of its metal to the solution, from which the electrical action would afterwards withdraw * La Lumiere Electrique, 1881. 44 2 ELECTRO-METALLUKGY. it. In order to realise these conditions, I have placed in a rectangular vessel either a weak solution of sulphate of copper, or some ordinary acidulated water, such as is used in voltameters. I then place in the solution a copper plate as a negative electrode, and for a positive elec- trode a piece of carbon surrounded by pulverised ores and contained either in a linen bag or in a porous cell, or even at the bottom of the electrolytic cell, and without any diaphragm. "With the electro- motive force of one or two Bunsen cells, the reaction takes place rapidly enough, and especially when the ores are not separated by a resisting diaphragm ; in the case of the linen bag, the action is imme- diate. I have successively operated on two qualities of ores. The first one was cupriferous iron pyrites containing 4-60 per cent, of copper, and in which the yellow copper pyrites with the iron pyrites forms a homogeneous mass. In the second ore the cupreous pyrites formed little agglomerations or spots disseminated in the mass ; the percentage was 3-60 per cent, of copper. After a few days' action of the battery, a notable proportion of the two ores was attacked, and the copper resulting from it was partially deposited on the negative electrode. But the attack, as I had anticipated, was attended with different results on the two ores. The first one, of homogeneous composition, had all its elements parallelly dissolved, so that the resi- due still gave 4/57 per cent, of copper after the action. The combi- nation of cupreous pyrites with the iron pyrites had, therefore, been dissolved in greater proportion than the martial pyrites." MRI. Bias and racist's Process. This process, which is too evidently based on the foregoing, was made known in the following year, namely in 1882. It is based on the following facts : I. The natural sulphides are, in certain degrees, conductors of the voltaic current. 2. The sulphuretted ores (mixtures of sulphides and gangues) are conductors of the current, even when the proportion of gangue is large. 3. If a solution of a salt, the acid of which attacks the natural sulphides, is electrolysed by using the latter as anodes, the metal of the sulphide is dissolved, whereas the sulphur remains deposited on the anode. It is with the nitrates that this operation is more easily conducted, and in this case without the formation of sulphate. The inventors describe the reactions which occur in a bath of nitrate of lead, in which a galena anode and insoluble metal cathode were used. The lead under the action of the current passes to the cathode, and the acid is liberated at the anode, where it attacks the galena, and regenerates the nitrate of lead, the bath remaining neutral and per- manent in action. The sulphur being separated can be readily re- moved. In carrying out their process, MM. Bias and Meist first agglomerate the ores by heat and compression. The ore being crushed into small grains, is introduced into copper moulds, and submitted to ELECTEIO SMELTING. 443 a pressure of 100 atmospheres, the mould is then closed and heated in a furnace to about 600 0. ; it is again pressed on removal from the furnace, and afterwards rapidly cooled to facilitate the removal of the ore plates. Thus prepared, the ore plates are attached to iron bars, which are connected by means of iron conductors to the positive pole of a dynamo -electric machine, and suspended in the bath, which con- sists of a solution of a neutral metallic salt suitable to the nature of the ore under treatment : nitrate of lead being used for galena ; nitrate, sulphide or chloride of zinc being used for zinc blende. In treating a compound ore, the bath is formed in accordance with the various metals of which it is composed. The cathodes employed consist of plates of metal insoluble in the bath, and connected by iron conductors to the negative pole of the dynamo -electric machine. The baths may be joined for tension or quantity, but preferably the former, whereby the fullest metallic deposit is obtained with a minimum of current. It must be borne in mind that in treating ores by either of the above processes, the bath must of necessity become impregnated with soluble earthy matter, which in time must seriously affect its conduc- tivity, to overcome which a great expenditure of electricity would be necessary. It has yet to be seen whether this insuperable objection to the direct treatment of metallic ores by electrolysis can be overcome. It will naturally suggest itself that a preliminary roasting would be advantageous. In the case of copper, there can be little doubt that the combined processes of smelting and electrolytic refining are by far the most certain and practical, if not the most economical, method of treatment, more especially as the gold and silver are by this method entirely recovered, while the copper itself is obtained in a chemically pure state when the process is properly conducted. Werdermann's Process. This process, which was submitted to trial in America some years ago, consisted in passing a powerful current into the furnace while the ores were in a state of fusion ; the process, however, was not successful, and the inventor subsequently devised the following process. The ores containing some precious metals associated with antimony, arsenic, sulphur, and other sub- stances, were first subjected to oxidation by means of ozone ; after oxidation and lixiviation, the silver was deposited from the solution by electrolysis ; the gold and silver remaining in the deposit were recovered by amalgamation, which was facilitated by moistening the ore with a solution of caustic alkali, and by connecting the agitating apparatus of the amalgamating vessel to the negative pole of a battery, the positive pole being connected to the vessel itself. Electric Smelting. The great success which has attended the electrolytic method of refining metals, but more especially copper, 444 ELECTRO-METALLURGY. is believed by many to be but the forerunner of a still wider application of the electric current, namely, the reduction of metals from their ores, in the "dry" way, by means of electricity. The fact that sulphides are known to be conductors of electricity, and, moreover (as lately shown by Mr. Bid well), are capable of accumu- lating or storing up the current, lead some persons to believe that the reduction of ores by electricity may at some future period supplant the ordinary processes of furnace smelting. Be this as it may and which time alone will determine a very interesting result in this direction has lately been achieved in the United States, which is likely to prove of great importance in the production of one or two refractory but important substances aluminium and its alloys, and silicon bronze. Cowles' Process. The following account of the methods adopted by the Cowles Electric Smelting and Aluminium Company, of Cleve- land, Ohio, was given in the New York Engineering and Mining Journal,* and will be read with considerable interest. The Company referred to is, it appears, carrying on electric smelting commercially, but at present are chiefly devoting themselves to the production of aluminium and silicon bronze. The system, however, may hereafter be extended to other metals, and the operations be conducted upon a more extended scale. The Messrs. Cowles have succeeded in greatly reducing the market value of aluminium and its alloys, and thereby vastly extending its uses ; they are said to be the largest pro- ducers in the world of these important products. As described in their patents, the Cowles process consists essentially in the use, for metallurgical purposes, of a body of granular material of high resist- ance or low conductivity, interposed within the circuit in such a manner as to form a continuous and unbroken part of the same, which granular body, by reason of its resistance, is made incandescent, and generates all the heat required. The ore or light material to be reduced as, for example, the hydrated oxide of aluminium, alum, chloride of sodium, oxide of calcium, or sulphate of strontium is usually mixed with the body of granular resistance material, and is thus brought directly in contact with the heat at the points of genera- tion. At the same time the heat is distributed through the mass of granular material, being generated by the resistance of all the granules, and is not localised at one point or along a single line. The material best adapted for this purpose is electric light carbon, as it possesses the necessary amount of electrical resistance, and is capable of endur- ing any known degree of heat, when protected from oxygen, without disintegrating or fusing ; but crystalline silicon or other equivalent of * Engineering and Mining Journal. New York. August 8th, 1885. COWLES PROCESS. 445 carbon can be employed for the same purpose. This is pulverised or granulated, the degree of granulation depending upon the size of the furnace. Coarse granulated carbon works better than finely pulverised carbon, and gives more even results. The electrical energy is more evenly distributed, and the current cannot so readily form a path of highest temperature, and consequently of least resistance, through the mass along which the entire current or the bulk of the current can pass. The operation must necessarily be conducted within an air- tight chamber or in a non- oxidising atmosphere, or otherwise the carbon will be consumed and act as fuel. The carbon acts as a deoxidising agent for the ore or metalliferous material treated, and to this extent it is consumed, but otherwise than from this cause it remains unimpaired. Fig. 122. Fig. 122 of the accompanying drawings is a vertical longitudinal section through a retort designed for the reduction of zinc ore by this process, and Fig. 123 is a front elevation of the same. Fig. 124 (ia a perspective view of a furnace adapted to withstand a very high tem- perature, and Figs. 125 and 126 are re- spectively longitudinal and transverse sections of the same. This retort consists of a cylinder, A, made of silica or other non-conducting material, suitably im- bedded in a body, B, of powdered char- coal, mineral wood, or of some other material which is not a good conductor p. of heat. The rear end of the retort cylinder is closed by means of a carbon plate, 0, which plate forms the ELECTRO-METALLURGY. 446 positive electrode, and with this plate the positive wire of the electric circuit is connected. The outer end of the retort is closed by means Fig. 124. of an inverted graphite crucible, D, to which the negative wire of the electric circuit is attached. The graphite crucible serves as a "^ (c Fig. 125. plug for closing the end of the retort. It also forms a condensing chamber for the zinc fumes, and it also constitutes the negative electrode. The term " electrode " is used in this case as designating the terminals of the circuit proper, or that portion of it which acts simply as an electrical conductor, and not with the intention of indicating the tig. 120. ends Q a j^ Between w hich there is no circuit connection. The circuit between the " electrodes," so called, is continuous, being established by means of, and through the body of, broken carbon contained in the retort A. There is no deposit made on either plate of the decomposed constituents of the material reduced. The mouth of the crucible is closed with a luting of clay or otherwise, and the opening d made in the upper side of the crucible, near its extremity, comes entirely within the retort, and forms a passage for the zinc fumes from the retort chamber into the condensing chamber. The pipe E serves as a vent for the condensing chamber. The zinc ore is mixed with pulverised or granular carbon, and the retort charged nearly full through COWLES' PROCESS. 447 the front end with the mixture, the plug 1 D being removed for this purpose. A small space is left at the top, as shown. After the plug has been inserted and the joint properly luted, the electric circuit is closed, and the current allowed to pass through the retort, traversing its entire length through the body of mixed ore and carbon. The carbon constituents of the mass become incandescent, generating a very high degree of heat, and being in direct contact with the ore the latter is rapidly and effectually reduced and distilled. The heat evolved reduces the ore and distils the zinc, and the zinc fumes are condensed in the condensing chamber, precisely as in the present method of zinc -making, with this important exception, that, aside from the reaction produced by heating carbon in the presence of zinc oxide, the electric current, in passing through the zinc oxide, has a decomposing and disintegrating action upon it, not unlike the effect produced by an electric current in a solution. This action accelerates the reduction and promotes economy in the process. Another form of furnace is illustrated by Fig. 124, which is a perspective view of a furnace adapted for the reduction of ores and salts of non- volatile metals and similar chemical compounds. Tigs. 125 and 1 26 are longitu- dinal and transverse sections respectively, through the same, illustrat- ing the manner of packing and charging the furnace. The walls and floor, L i/, of the furnace are made of fire-bricks, and do not necessarily have to be very thick or strong, the heat to which they are subjected not being excessive. The carbon plates are smaller than the cross- section of the box, as shown, and the spaces between them and the end walls are packed with fine charcoal. The furnace is covered with a removable slab of fire-clay, N, which is provided with one or more vents, n, for the escaping gases. The space between the carbon plates constitutes the working part of the furnace ; this is lined on the bottom and sides with a packing of fine charcoal, o, or such other material as is both a poor conductor of heat and electricity as, for example, in some cases silica or pulverised corundum or well-burned lime and the charge, P, of ore and broken, granular, or pulverised carbon occupies the centre of the box, extending between the carbon plates. A layer of granular charcoal, o, also covers the charge on top. The protection afforded by the charcoal jacket, as regards the heat, is so complete that, with the covering slab removed, the hand can be held within a few inches of the exposed charcoal jacket ; but with the top covering of charcoal also removed, and the core exposed, the hand cannot be held within several feet. The charcoal packing behind the carbon plates is required to confine the heat, and to protect them from combustion. With this furnace aluminium can be reduced directly from its ores, and chemical compounds from corundum, cry so - lite, clay, c., and silicon, boron, calcium, manganese, magnesium, ELECTKO-METALLURGY. and other metals are in like manner obtained from their ores and com- pounds. The reduction of ores, according to this process, can be practised, if circumstances require it, without any built furnace. At present the Cowles Company is engaged mostly in the producing of aluminium bronze, and aluminium silver and silicon bronze. The plant, were it run to its full capacity, is capable of turning out 80 Ibs. of aluminium bronze, containing 10 percent, of aluminium, daily ; or, if run upon silicon bronze, could turn out 120 Ibs. of that per day, or, it is said, more aluminium bronze daily than can be produced by all other plants in the world combined. This production, however, is but that of the experimental laboratory, and arrangements are making to turn out a ton of bronze daily, and the works have an ultimate capacity of from 8,000 to 10,000 horse-power. The energy consumed by the reduction of the ore is almost entirely electrical, only enough carbon being used to unite with the oxygen of the ore to carry it out of the furnace in the form of the carbon monoxide, the aluminium remaining behind. Consequently, the plant necessary to produce aluminium on a large scale involves a large number of the most powerful dynamos. The retail price of standard IO per cent, aluminium bronze is one dollar per pound avoirdupois, which means less than nine dollars per pound for aluminium, the lowest price at which it has ever been sold ; yet the Cowles Company has laid a proposition before the Government to furnish this same bronze in large quantities at very much lower prices than this. The Hercules alloy, castings of which will stand over 100,000 Ibs. to the square inch tensile strain, sells at seventy-five cents, a pound, and is also offered the Government or other large consumers at a heavy discount. The alloys are guaranteed to contain exactly what is advertised ; they are standardised into 10 per cent., 7*5 percent., 5 per cent., and 25 percent, aluminium bronze before shipment. The current available at the Cowles Com- pany's works was, until recently, 330 amperes, driven by an electro- motive force of no volts and supplied by two Edison dynamos ; but the Company has now added a large Brush machine that has a cur- rent of 560 amperes and 52 volts electromotive force. Since the above results were obtained, Messrs. Cowles have made considerable advance in the working of their process, in which they have been aided by the chemical skill of Professor C. F. Mabery, who is associated with them in some of their patents. In a paper read before the American Institute of Mining Engineers at Halifax,* Dr. T. Sterry Hunt, who had devoted two entire days at the experimental works at Cleveland, furnished some additional particulars concerning this interesting and valuable process, from which we make a few * American Engineering and Mining Journal, September igth, 1885. COWLES* PEOCESS. 449 extracts, feeling confident that this important application of elec- tricity will receive the fullest attention on this side of the Atlantic. Dr. Hunt says, " If alumina, in the form of granulated corundum,* is mingled with the carbons in the electric path, aluminium is rapidly liberated, being in part carried off with the escaping gas, and in part condensed in the upper layer of charcoal. In this way are obtained con- siderable t masses of nearly pure fused aluminium and others of a crystal- line compound of the metal with carbon. When, however, a portion of granulated copper is placed with the corundum, an alloy of the two metals is obtained, which is probably formed in the overlying stratum, but at the close of the operation is found in fused masses below. In this way there is got, after the current is passed for an hour and a half through the furnace, from 4 to 5 Ibs. of an alloy containing from 15 to 20 per cent, of aluminium, and free from iron. On substituting this alloy for copper in a second operation, a com- pound with over 30 per cent, is obtained The reduction of silicon is even more easy than that of aluminium. "When silicious sand, mixed with carbon, is placed in the path of the electric current, a part of it is fused into a clear glass, and a part reduced, with the production of considerable masses of crystallised silicon, a portion of this being volatilised and reconverted into silica. By the addition of granulated copper, there is readily formed a hard brittle alloy holding 6 or 7 per cent, of silicon, from which silicon bronzes can be cheaply made. " The direct reduction of clay gives an alloy of silicon and alumi- nium, and with copper, a silico- aluminium bronze that appears to possess properties not less valuable than the compound already men- tioned. Even boric oxide is rapidly reduced, with evolutions of copious brown fumes, and the formation, in presence of copper, of a boron bronze that promises to be of value, while, under certain conditions, crystals of what appear to be the so-called adamantoid boron are formed. In some cases also crystalline graphite has been produced, apparently through the solvent action of aluminium upon carbon." Dr. Hunt states that remarkable results are obtained by alloying small quantities of aluminium with an admixture of copper and nickel, one of these compounds having broken with a strain of m,ooo Ibs. to the square inch, with an extension of iiroths, while a 10 per cent, aluminium bronze broke with 109,000 Ibs. He further * Corundum is a very hard genus of aluminous minerals, to which the gems sapphire, ruby, salamstein, and adamantine spar belong. Emery is an impure, compact, amorphous, and opaque variety of corundum, and consists, according to Tennant, of alumina, 80 ; silica, 3 ; iron, 4 parts. G G 450 ELECTRO-METALLURGY. states that an addition of from two to three per cent, of aluminium to brass greatly increases its tensile strength, while rendering it less susceptible to oxidation. Fig. 127. By a recent improvement in the Cowles furnace, the copper or other metal used for the alloy is in the form of rods running across the furnace, it having been found that where grains of copper were used, they sometimes fused together in such a manner as to short circuit the current. The new electric smelting furnance is shown in Tigs. 127, 128. CHAPTER XXXII. MECHANICAL OPERATIONS CONNECTED WITH ELECTRO-DEPOSITION. Metal Polishing. 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. Metal Polishing. All articles which are required to be bright when finished are submitted to the process of polishing before they undergo the preliminary operations of cleaning, dipping, quicking, &c., to prepare them for the depositing vat. If the articles were not to be rendered perfectly smooth before being coated with other metal, it would be exceedingly difficult, if not impossible, either to polish or burnish them after being plated to such a degree of perfection as is necessary for bright work. This preliminary polishing is more especially necessary in the case of nickel-plated work, for unless the work is rendered bright and absolutely free from scratches or markings of any kind, these defects will inevitably show when the articles are finished. The extreme hardness of nickel renders the operation of polishing and finishing nickel-plated work at all times laborious, but more especially so if the work has been badly polished before it enters the nickel bath. It is also the fact that every scratch, however minute, which a careless polisher leaves upon brass, copper, or steel work, becomes plainly visible after it has been finished by the nickel- polisher. In large work, such as mullers, sausage- warmers, &c., the preparatory polishing should be of the most faultless character, since any attempt to remedy defects after nickel-plating would be fruitless, and probably result in cutting through the nickel, necessitating the replating of the article, which should under all circumstances be rigidly avoided. It should be the nickel-plater's./?^ duty to examine every piece of work, to see if it has been properly polished, before placing it in the potash bath ; if badly polished, it must be sent back to the polisher again. Brass Polishing. These operations are performed at a lathe set in motion by steam-power. It is usually the practice for metal polishers 45 2 MECHANICAL OPERATIONS, ETC. to fix their lathes in workshops supplied with steam-power from adjacent premises, the cost of power per lathe being generally moderate. The Polishing Lathe. This machine ordinarily consists of a stout wooden bench set firmly in the floor. In the centre of the bench is a solid cast-iron standard secured in its position by screwed bolts in which runs a long double spindle, working on brass or gun-metal bearings. In the centre of the spindle are two pulleys, one fast and the other loose, by means of which it may be set in motion or stopped at will. The spindle revolves at a very high speed. A leather belt, connected to a revolving shaft, by preference below the lathe, passes over these pulleys, and either workman, by means of a stick kept for the purpose, can, by pushing the belt to left or right, set the spindle in motion or stop it as occasion may require. This arrangement is not only convenient, but absolutely necessary, since the spindle is gene- rally worked by two men one at each end ; and when either of them requires to change one circular buff, or "bob," for another, which very frequently happens, he takes up the short stick and pushes the belt from the fast pulley, which is attached to the spindle, to the loose pulley, which runs over it. An improved polishing lathe, with shaft- carrier and standard combined, introduced and manufactured by Carlyle, of Birmingham, is shown in Fig. 129. This useful arrange- ment obviates the necessity of fixing a wooden bench. The polishing tools, or "bobs," as they are usually called, con- sist of discs of various kinds of hard leather, the stoutest of which are about three -fourths of an inch thick, and are made from walrus or hippopotamus hide ; other bobs are made from bull-neck leather, felt, &c. The materials used for brass polishing are glass-cutters' sand and Trent sand ; the former, having a sharper cut than the latter, is generally used for very rough work, such as comes direct from the founders, with the file marks extensively visible upon its surfaces. Before commencing his work, the polisher, after removing his coat and hat, envelops himself in ' a long, loose garment, made fof brown holland, which buttons at the neck from behind, and its sleeves are secured at the wrists in the same way. Previous to setting the lathe in motion, each polisher spreads a square piece of calico upon the bench, immediately under the point of each spindle, upon which each workman places a quantity of the sand he intends to use. The first operation, called roughing, or rough sanding, is generally performed by the workman standing at the right-hand end of the spindle, and the work is then passed to his mate on the left, who treats it with a finer quality of sand, or " old sand," that which has been repeatedly used, by which a much smoother surface is produced. In the process of sanding, as it is called, THE POLISHING LATHE. 453 the workman, holding a piece of work in his right hand, takes up a handful of sand with his left, and holding the work up to the lower part of the revolving bob, presses it against it, while he dexterously allows the sand in his left hand to continually escape, by which it passes on to the bob while the work is being pressed against it ; the moment the handful of sand is paid out, he takes up another handful, Fig. 129. almost involuntarily, and keeps up this movement, at intervals of a few seconds only, with mechanical regularity. The operation of rough sanding is sometimes very laborious, as the workmen have to press with all their force upon the work, in order to obliterate deep file marks and other irregularities. 454 MECHANICAL OPERATIONS, ETC. Brass Finishing. After the work has been rough and fine sanded, it is transferred to the finisher, in whose hands it receives the highest degree of polish of which the metal is susceptible. As in all other branches of trade, there is much difference in the skill and judgment of those who follow the art of brass finishing. While some workmen take great delight in turning their work out of hand in the most creditable condition, others are exceedingly careless and indifferent as to whether the work be good or bad, having, perhaps, a preference for the latter. The material generally used for finishing brass work is quicklime reduced to a fine powder, and sifted through a muslin sieve. The lime preferred for this purpose is obtained from the neighbour- hood of Sheffield, and is well known in the polishing trade as "Sheffield lime." This material is selected at the lime-kilns by persons who well know what the trade require, and is packed in casks and sent to the polishers in London or elsewhere, who preserve it in olive jars, or large tin chests, carefully covered with cloths to exclude the air ; if the lime be allowed to extract carbonic acid from the atmosphere it soon becomes converted into carbonate of lime, which is useless for polishing purposes. When the lime is required for use, a boy takes a lump or two from the jar, and removes all dirt and impurities by first scraping the lime all over, after which he breaks the lime up into small fragments, a few of which he puts into an iron mortar, and with a pestle of the same metal reduces it to a powder. He next passes the powdered lime through the sieve and hands the fine powder to the first workman who requires it. Only a small quantity of lime is thus prepared at one time, since it loses its cutting property if exposed to the air even for a short time, especially when in the state of powder. Lime Finishing is generally entrusted to workmen of superior ability, since much of the beauty of the work depends upon the care and skill bestowed upon this stage of the polishing process. The lime is applied to the bobs in the same way as the sand, but a little oil is also used ; by being used over and over again, the lime becomes im- pregnated with particles of metal, which increases its polishing power. Indeed, we may say that the bright polish which metals acquire when rubbed with an impalpable powder, such as jewellers' rouge, lime, or other material, is only due to the polishing medium indirectly ; it is the metal which becomes removed from the surface of the work which produces the brilliant effect termed finish, or high polish. When the workman has carefully gone over every part of the work, changing the bobs from time to time to suit the various surfaces plane or hol- low, as the case may be he removes the lime-bob from the spindle, and fixes a "dolly" in its place. The dolly for this purpose com- monly consists of a large disc, composed of many layers of unbleached POLISHING SILVER OR PLATED WORK. 455 calico the whole being about half to three-quarters of an inch in thickness. The folds of calico are first cut into a circular form by means of a chisel and mallet, and these are braced together by two discs of leather or metal, secured by copper rivets. A hole is formed in the centre to admit the screwed point of the spindle. The dolly is worked with dry lime, which is applied by frequently holding a lump of fresh lime against the revolving calico disc, by which it becomes sufficiently charged for the time. The high speed at which the dolly revolves causes the frayed edges of the cloth, when charged with dry lime, to produce an exceedingly brilliant surface in a very short time, but much judgment on the part of the finisher is needed to produce the highest finish attainable, a point which good workmen never fail to reach. Nickel Polishing, or Finishing, is performed by aid of Sheffield lime, a little oil being applied to the bobs occasionally. Rouge and crocus compositions are used by preference by some polishers. If the work has been properly polished before plating, the nickel-finisher's task, although requiring much skill and care, is tolerably straightfor- ward. The dull nickel deposit readily yields to the pressure upon the lime -bob, presenting to the eye of the workman that degree of bright- ness which he knows full well will come up to the highest possible brilliancy under the operation of the dolly. He takes good care, how- ever, not to trust too much to the latter tool, but gives the work a brilliant surface before it is submitted to the dolly. It is his special care, moreover, by using small and thin bobs, specially reserved for such purposes, to well polish every interstice or hollow that can be reached by the smallest of his bobs, some of which are about the size of a crown piece. Steel Polishing. The articles are first ground upon a grindstone or emery wheel, and are afterwards glazed, as it is termed, which con- sists in submitting the steel articles to the action of round discs of wood covered with leather or metal a mixture of lead and tin applied with emery powder of various degrees of fineness, moistened with a little oil. By this means the work is rendered as smooth as possible, and afterwards receives a bright finish with leather-faced buffs charged with finely powdered crocus (peroxide of iron), which imparts to the surface the brilliant lustre for which good steel, as a metal, is so justly famed. Cow-hair or bristle brushes charged with crocus and oil are also used for steel polishing. Polishing Silver or Plated Work. The preliminary stages of the process are performed at a lathe set in motion by steam-power, or by a suitable foot-lathe ; the ordinary form of the latter machine is shown in Fig. 130. The tools used are a series of circular buffs or bobs con- sisting of discs of wood, faced with hard and soft leathers to suit the 456 MECHANICAL OPEEATIONS, ETC. several stages of the process, the softer buffs being- applied after the articles have received a preliminary treatment with the harder and more active tools. Circular brushes, formed of bristles set in discs of wood, are also employed, and for some purposes bobs made from bull- neck leather, &c., of various sizes and degrees of thickness, are used. The polisher is generally provided with the various kinds of leather required in his work, from which he cuts out his bobs to suit the particular work he may have in hand. The polishing is Fig. 130. effected with the material known as rotten- stone, or tripoli, moistened with oil ; the former is usually kept in a shallow tray, and the latter in a conical tin can with small tubular opening at the top ; by gently pressing upon the bottom of the can with the thumb, the oil escapes slowly, so that a single drop may be applied if necessary. Having set the lathe in motion, the workman applies a little rotten- stone and oil, in the form of a paste, to the revolving bob, and then presses the article with moderate force against it, shifting the article continu- ally, until the entire surface has been buffed. The work is carefully examined from time to time, and when sufficiently smooth for finish- POLISHING SILVER OR PLATED WORK. 457 ing, it is sent to the finishing room, where it is first cleaned by well washing with warm soap and water, with the addition of a little soda. Finishing, or Colouring, is performed either by lathe or by hand, according to the nature of the work. When the lathe is employed, a a mop or " dolly," made from the fabric called swansdown, is used, in which several layers of this material, cut into a circular form, are united by discs of wood or metal held together by screws or rivets. In the centre of these discs a hole is punched, to receive the screwed point of the spindle. The material used for finishing is the finest quality of jewellers' rouge (peroxide of iron), which is made into a paste with water, and applied, in small quantities at a time, to the face of the dolly-mop, which, by revolving at a very high speed, quickly pro- duces a remarkably brilliant lustre. The rouge "compo" before referred to is also used for silver polishing. Hand -Finishing, or Colouring. This operation is best conducted by men or women whose hands are of a soft texture, or have a ' ' velvet- hand," as it is sometimes termed in the trade. The colourer is pro- vided with a shallow porcelain vessel, in which he puts a quantity of rouge, and pours upon it sufficient water to form a pasty mass ; after having thoroughly cleaned the articles, and wiped them dry with a soft piece of diaper, he dips the tip of his finger in the rouge-paste, and smears it over a part of the work, and rubs the article briskly with the side of the hand below the little finger, or the large muscle below the thumb, according to the surface he has to treat, using moderate pressure at first, and this he diminishes as the work approaches the finish. As soon as the silver surface has acquired the black lustre for which this metal, when highly polished, is so remark- able, it is examined to ascertain if there are any scratches or other imperfections visible ; if an appearance of greyness is noticeable upon any part of the work, such portions are again gone over until the uni- form black lustre has been produced. It is of the highest importance that neither dust nor grit should get into the rouge or upon the work while being coloured, otherwise scratches difficult to obliterate will be produced. When the work is finished, the rouge is washed out of the crevices, or ornamental parts of the work by means of soap and water and a very soft long-haired brush kept specially for this purpose. The articles are then wiped dry with a soft piece of old diaper or linen, and afterwards with a soft chamois leather. Articles which have been electro -plated should only be submitted to the process of polishing when they have received a stout coating of silver, for if but a moderate deposit has been put upon the work, the severe operation of buffing with rotten -stone will most probably cut through the silver and expose the metal beneath, more especially at the edges. 458 MECHANICAL OPERATIONS, ETC. Burnishing. Although many stoutly plated articles of electro- plate especially spoons and forks are rendered bright by polishing, by far the greater proportion of this class of work is burnished. Burnishers are an important class of female operatives, who have regularly served an apprenticeship to the trade from an early age, and many of whom perform their allotted tasks with exquisite care and finish. The tools employed in burnishing silver and plated work are very numerous, and are made of steel for the preliminary operations of grounding as it is termed, and blood-stone, a hard compact variety of haematite (native oxide of iron) for finishing. A few examples of burnishing tools are shown in the accom- panying engravings (Fig. 131), the cuts being about half the actual size of the tools they represent. The steel tools, which are made in various forms to suit the different surfaces to which they have to be applied, are of various degrees of thick- ness, the thinner or keener implements being first used to ground the work, as it is termed, before the stouter tools are applied. The blades of the steel burnishers are fixed into wooden hafts or handles provided with a brass or iron ferrule, to pre- vent the wood from split- ting. The blood -stones are fitted into iron tubes, and secured by means of pewter solder, a wooden handle being inserted in the other end of the tube. Blood-stone burnishers are of several qualities, the finest material being used for finishing. These imple- ments are also of different sizes, so as to be suitable for large or small surfaces. Preparing the Tools for Burnishing. To impart a perfectly smooth and bright surface to the steel and blood -stone burnishers, each work- woman provides herself with two flat buffs, one for the steel tools and the other for the blood- stones. The steel buff consists of a piece of buff (Fig. 132) or belt leather, such as soldiers' belts are made Fig. 131. BURNISHING. 459 from, about 10 inches long and 2\ inches wide. The leather is first boiled for some time in water, after which it is dried as speedily as possible, by which means it becomes excessively hard ; the leather is next glued to a flat piece of wood, about three -fourths of an inch larger than itself each way, and about three-quarters of an inch in thickness. To secure the leather in its position until the glue has become hardened, a heavy weight or clamps are used. "When ready for use, the burnisher forms a groove from end to end, by rubbing one of the stouter tools upon the surface of the leather, leaning with all her weight upon it, so as to form as deep a hollow or groove as possible. Having done this she places a little jewellers' rouge in the groove, Pig_ 2. and passes the tool up and down the hollow with all her force, until its face has acquired a bright black lustre. It is usually the practice to form about three such grooves in the leather with tools of various thicknesses, these being applied to stout or thin burnishers, as the case may be. The buffs for polishing the blood- stone tools are prepared in the same way as the former, a single groove or channel only being formed as evenly as possible in the centre of the leather. The material employed in polishing the face of the blood- stone is putty-powder (oxide of tin), which is used in the same way as the rouge for the steel tools. Preparation of the Work for Burnishing. The plated articles, after being scratch -brushed, rinsed, and dried, are transferred to the bur- nisher, who first scours them all over with fine silver-sand and warm soap and water, applied with a piece of soft flannel ; the work is then thoroughly well rinsed in warm water, then wiped dry with soft diaper or old linen rag. "When thus prepared, the article is ready for burnishing. Burnishing Silver or Plated Work. After scouring the work the burnisher makes a small quantity of warm soap-suds, in a gallipot or other small vessel, by putting a few thin sli ces of yellow soap in the vessel, and pouring hot water over them, stirring for a few moments with one of the steel tools, until the " suds" are in a condition for use. She next selects the tool she intends to commence with, and rubs it upon the buff until the requisite surface is obtained. Having wiped the tool, she dips it in the suds, and holding it in her right hand, with the handle resting on her little finger, near the knuckle, the other three fingers being above the handle, while the thumb presses upon the top of the handle, by which means the tool is held firmly, and can be applied with the necessary pressure. The first tool employed for a large flat surface is one of the larger and thinner burnishers, whose face is of an elliptic form ; this is held in a slanting 460 MECHANICAL OPERATIONS, ETC. direction, and passed to and fro over the work with sufficient pres- sure to produce a certain degree of brightness, and every now and then the tool is wiped dry, re-buffed, and again applied, until the whole surface of the article has been gone over. A stouter steel tool is next applied, which has the effect of considerably erasing the marks left by the first implement. After going over the surface several times with steel tools of increasing thickness, the first blood- stone is next applied, and which, having a broad and highly polished surface, nearly removes all traces of the marks produced by the steel tools. The work is afterwards gone over with a, finishing stone, which is of the finest quality of blood -stone that can be procured. Electro-gilt Work is burnished in the same way as the preceding, but some burnishers prefer using vinegar instead of soap-suds for moistening their tools. "We suggested the employment of weak ale for this purpose, and the workwomen having tried it, used it con- stantly with much satisfaction at our own works for many years. CHAPTER XXXIII. RECOVERY OF GOLD AND SILVER FROM WASTE SOLUTIONS, ETC. Recovery of Gold from Old Cyanide Solutions. Recovery of Silver from Old Cyanide Solutions. Extraction of Silver by the Wet Method. Recovery of Gold and Silver from Scratch-brush Waste. Recovery of Gold and Silver from Old Stripping Solutions. Recovery of Gold from Old Cyanide Solutions. Since the precipitation of gold (and silver) from cyanide solutions, which is effected by means of mineral acids, involves the liberation of hydro- cyanic acid (prussic acid) the operations must always be conducted with the Titmost caution, and should always be carried on in the open air. It is well to remark here that when acid is added to a cyanide solution, not only hydrocyanic acid but also carbonic acid is liberated ; and since this heavy gas cannot escape through the flue of an. ordinary chimney, owing to its gravity, but flows over the vessel in. a dense white vapour, the operator should be careful not to disturb these fumes, so as to cause them to rise upward, but to allow them to. flow over the sides of the vessel and escape into the open air, where they will be dispersed by the wind. The reduction of the gold by the dry iv ay is, however, less hazardous, not so offensive, and fully as economical. To precipitate gold from cyanide solutions, hydrochloric acid is to be gradually added, until no further precipitation takes place ; the solution should then be boiled and the vessel set aside to cool. The precipitate (cyanide of gold), which is of a yellowish, colour, must then be separated from the supernatant liquor by decantation, and then filtered. Since a small portion of gold, however, still remains in the liquor, it must not be thrown away, but should be heated, and zinc filings added, which, will throw down the remainder of the gold ; the clear liquor is now to be poured off, and the residue boiled with dilute hydrochloric acid, to remove excess of zinc, and after washing, the deposit is to be added to the other portions. Ignite and fuse the mixture in a platinum or ordinary crucible, with an equal weight of sulphate of potassium. Dissolve the saline residue in boiling sul- 462 RECOVERY OF GOLD AND SILVER FROM WASTE SOLUTIONS. phuric acid, then wash it with water, when perfectly pure gold will remain. (R. Huber.)* Bottger recommends the following method for recovering gold from old solutions : The solution should be evaporated to dryness, the residue then finely powdered, and intimately mixed with an equal weight of litharge (oxide of lead) and fused at a strong heat ; the lead is extracted from the resulting button of gold and lead alloy by warm nitric acid, when the gold will remain as a loose brown spongy mass. The same author says, " If we pour hydrochloric acid into a pure solution of gold in cyanide of potassium, there is slowly formed at ordinary temperatures, and immediately on the application of heat, a yellow precipitate, which is cyanide of gold ; the filtered liquid which has given this precipitate still contains a little gold in solution. On evaporating the liquid to dryness, fusing, dissolving, and filtering afresh, there remains upon the filter the remainder of the gold. Crystallised double cyanide of gold and potassium fuses and effer- vesces by heat, and is resolved into cyanogen gas, ammonia, and cyanide of potassium, if air be present ; its complete decomposition requires a strong heat. When it is strongly ignited, mixed with an equal weight of carbonate of potash, a button of metallic gold is obtained." Cyanide gilding solutions, when mixed with sulphuric, nitric, or hydrochloric acid, slowly deposit cyanide of gold ; and when boiled with hydrochloric acid, it is completely resolved into cyanide of gold and chloride of potassium. The same result is obtained with nitric and sulphuric acid, and even with oxalic, tartaric, and acetic acids. When heated with sulphuric acid, it gives off hydrocyanic acid gas, and after ignition, leaves a mixture of gold and sulphate of potassium. Iodine sets free cyanogen gas, forms iodide of potassium, and throws down the cyanide of gold. (Bottger.} Gold may be precipitated from washing waters containing traces of the precious metal by adding a solution of protosulphate of iron, when a brown deposit of pure gold is obtained ; the subsidence of the metal may be hastened by heating the liquid. Recovery of Silver from Old Cyanide Solutions. Eisner made a series of important researches upon the extraction of gold and silver from cyanide solutions, the results of which he communicated in a valuable paper, from which the following extracts are taken. He pre- faced his description of the practical methods recommended, by men- tioning the results of some of his experiments upon which they were based. I. " If we add hydrochloric acid to a solution of silver in cyanide of * Chemical News, vol. viii. p. 31. RECOVERY OP SILVER FROM OLD CYANIDE SOLUTIONS. 463 potassium until the liquid exhibits an acid reaction, we obtain a white precipitate of chloride of silver, which, when submitted to heat, melts into a yellow mass. If this was cyanide of silver, the application of a red heat would have left a regulus of silver. The addition of the hydrochloric acid precipitates all the silver present in the liquid in the form of chloride of silver. "If we evaporate a solution of silver in cyanide of potassium to dryness, and heat the residue to redness, until the mass is in a state of quiet fusion, and has assumed a brown colour, there remains, when we wash the mass with water, metallic and porous silver. The wash waters, when filtered, still contain a little silver in solution, because, if hydrochloric acid is added to them, it produces a precipitate of chloride of silver. In evaporating and calcining a solution of gold in cyanide of potassium, the result is similar, i.e. we obtain metallic gold. The wash waters, acidulated with hydrochloric acid, give, when treated with sulphuretted hydrogen, a brown precipitate of sul- phide of gold ; and with the salt of tin a violet precipitate (purple of Cassius), a proof that these liquids still contain a little gold in solution. "Extraction of Silver by the Wet Method Add hydrochloric acid until the liquid exhibits a strongly acid reaction. The precipitate of chloride of silver which is thus obtained, will be, as we have already said, of a reddish- white colour, because of the cyanide of cop- per which is precipitated with it when the solution has been used a long time for silvering objects containing copper. In this precipita- tion by hydrochloric acid, there is hydrocyanic acid gas set free, there- fore the operation should only be performed in the open air, or in a place where there is good ventilation ; if the precipitate is very red, it must be treated with hot hydrochloric acid, which will dissolve the cyanide of copper. The chloride of silver, having been washed with water, must be dried and then fused with pearlash in a Hessian crucible coated with borax, in the ordinary manner for obtaining metallic silver. " This method is very simple in its application, and very economi- cal, considering that by the aid of the hydrochloric acid all the silver contained in the solution of cyanide of potassium is precipitated, and there remains no trace of it in the liquid. But the quantity of hydro- cyanic gas which is disengaged is a circumstance which must betaken into serious consideration when operating on large quantities of silver solution, the vapour of which is most deleterious, and nothing but the most perfect ventilation, combined with arrangements for the escape of the poisonous gases, will admit of the process being carried on with- out danger to the workmen ; when, however, we have taken the pre- cautions dictated by prudence, the method in question may be con- 46*4 BECOVERY OF GOLD AND SILVER FROM WASTE SOLUTIONS. sidered as perfectly practical. The liquid should be poured into very capacious vessels, because the addition of the acid produces a large amount of froth. " Extraction of Silver by the Dry Method. The solution of cyanide of silver and potassium is evaporated to dryness, the residue fused at a red heat, and the resulting- mass, when cold, is washed with water. The remainder is the silver in a porous metallic condi- tion. There still remains in the wash waters a little silver, which may be precipitated by the addition of hydrochloric acid." Recovery of Gold and Silver from Scratch-brush Waste. The sludge or sediment which accumulates in the scratch -brush box fre- quently contains a considerable quantity of gold and silver, removed by the brushes from articles which have stripped in parts owing to de- fective cleaning of the work. This waste, with other valuable refuse of a similar description, should be collected every few months, and after being dried, should be mixed with a little dried carbonate of potash and fused. The resulting button, being an alloy of gold, silver, copper, &c., may be treated as follows to separate the gold and silver : Remelt the alloy, and granulate it by pouring the molten metal into cold water. Place the grains in a flask and pour on them a mixture of 2 parts nitric acid to I part water, and apply moderate heat, when all but the gold will be dissolved, the latter remaining as a brown powder at the bottom of the flask. The liquid must then be care- fully poured into another vessel, and strips of clean copper immersed in it, which will cause any silver present to be thrown down in the metallic state. The gold and silver deposits must afterwards be well washed with warm water, and after drying, be mixed with dried carbonate of potash or soda, and fused as before. In fusing these fine deposits, after they have been intimately mixed with the dried alkali, which is to act as a flux, the mixture should be compressed as much as possible when placed in the crucible, or melting pot, by means of an iron pestle or other suitable tool, and the heat allowed to progress slowly at first, and after a short time this may be increased until the contents of the crucible assume a semi-fluid condition ; when in this state, the heat should be moderated, to allow the metal to ''gather," as it is termed, by which the molten globules will gradually subside and unite in the form of a liquid mass at the bottom of the pot. It is very important at this stage to keep the fused mass in as liquid a state as possible, taking care also not to apply too great heat, or the contents may rise up and overflow. Should this be likely to occur, a pinch of dried com- mon salt may be thrown into the pot, which will cause the fused mass to subside. When the operation is complete, the pot is to be with- drawn from the fire and placed aside to cool ; the pot is afterwards broken at its lower part, by a blow from a hammer, and the button EECOVEBY OF GOLD AND SILVER. 465 extracted. This may then be plunged into a dilute sulphuric acid pickle to remove any flux that may attach to it. Recovery of Gold and Silver from Old Stripping Solutions. The gold may be recovered from exhausted stripping baths by evaporating them to dryness and fusing the residue with a little carbonate of potash or soda. There are several methods of treating old silver stripping solutions, of which the following are the simplest : i . Dilute the liquid with three or four times its bulk of water ; now place in the liquid several stout plates of clean zinc, which will rapidly become covered with a spongy layer of reduced silver ; the plates should be occasionally shaken in the liquid to remove the deposited metal, which will fall to the bottom of the vessel. When the zinc plates, after having been immersed for a few hours, cease to become coated with silver, the liquid may be decanted into another vessel, and a few drops of hydrochloric acid added, when, if a white cloudiness is produced, more acid should be added (or a solution of common salt) until it produces no further effect. The white pre- cipitate, which is chloride of silver, may afterwards be collected and treated separately. The reduced silver in the first vessel should be well washed, to free it from sulphate of zinc, and afterwards dried and fused as before. 2. The silver stripping solution may be treated with a strong solution of common salt, which will throw down the metal in the form of chloride, and this, after being well washed, may be employed for making up a silver bath, or the chloride may be decom- posed and the silver reduced to the metallic state, with or without the aid of heat, by immersing in the deposit several stout pieces of clean zinc, which after awhile will convert the deposit into metallic silver in the form of a grey powder. To facilitate the action, a few drops of sulphuric acid should be added. After well washing with hot water, this powder may be dissolved in nitric acid, to form nitrate of silver, which can then be used for making up silver baths. Or the grey powder may be dried and mixed with dried carbonate of potash and fused as before directed. After putting the mixture of reduced silver and carbonate of potash into the crucible, it should be compressed as much as possible, by pressing it with an iron pestle, which will greatly facilitate the "gathering" of the globules of fused silver; indeed it is a good plan, when the crucible has become fully heated, to gently press the crust of unfused matter with an iron rod, so as to force it to the lower part of the vessel where the heat is greatest. When the gathering of the metal is complete, a small quantity of nitre may be occasionally dropped into the crucible, which will remove any traces of iron or copper that may be present, and thus render the silver button more pure. 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. " Stripping" Metals from each other. Old articles which have been gilt, silvered, or nickel-plated, or new work which has been unsuccessfully coated with these metals by electro-deposition, gene- rally require to be deprived of the exterior coating before a proper deposit can be obtained by electrolysis. The operation of removing the exterior layer of metal is technically termed stripping, and the various solutions applied for the purpose are termed stripping solutions. It may be well to remark here that metals of a like character do not adhere firmly to each other; thus electro-deposited gold will not adhere to a gilt surface, silver to a silver-plated surface ; nor will nickel attach itself to a nickel-plated article ; this fact is most con- spicuously observable when an attempt is made to re-nickel a nickel- plated article without previously removing the old layer of this metal, when the second coating will generally rise up from the under- lying coat, even without subjecting it to any provocation by me- chanical means, such as buffing. Indeed, so persistent is this metal in refusing to accept a second coating that we have known a brass rod (placed in the bath as a " stop," to check the force of the current when first filling the bath) which had remained in the bath for many weeks, to become coated with countless layers of nickel, which had partially separated from each other, giving the lower end of the rod the appearance of a metallic mop. The author's impression was that every time the circuit was broken, by the stoppage of the dynamo machine, that the layer next deposited, when the machine was again in motion, did not adhere to its predecessor, but became a distinct and separate layer. Although this refusal to attach itself to a metal of its own kind is not so marked in the case of silver and gold as with nickel (and we might say copper also), it is unquestionably the case STRIPPING SOLUTION. 467 that the latter metals will more firmly adhere, when electro -deposited, to copper, brass, or German silver, than they will to articles composed of or coated with the same metals. The solutions employed for removing or stripping the precious metals and nickel from articles which have been coated with them will be given under separate head- ings, since the materials employed differ in each case. Stripping Solution for Silver. A quantity of strong oil of vitriol is put into a stone jar or enamelled saucepan, heated on a sand- bath or in any convenient way, and to this is added a small quantity of saltpetre (nitrate of potash). Sometimes nitrate of soda, called Chili saltpetre, is used in place of the other salt. "When the saltpetre has become dissolved, which may be accelerated by stirring the mix- ture with a stout glass rod, the articles to be stripped, attached to a copper wire, are dipped into the hot liquid, and allowed to remain, with occasional motion up and down, until the whole of the silver has become dissolved off. If the operation be carefully watched, it will be observed that the silver quickly disappears from the parts where it was thinnest, and gradually appears to fade away until not a trace is left upon the article. The chemical action of the solution upon the German silver, brass or copper, of which the article may be com- posed, is very slight if the articles are withdrawn directly the silver has been removed. It is very important that no water should be allowed to enter the stripping bath ; therefore the articles should be perfectly dry before being immersed. In stripping spoons and forks, it will generally be noticed that the last portions of silver to leave the articles are at the points of the prongs and upper part of the handle of forks, and the lower portion of the bowls and extremity of the handle of spoons, which establishes the well-known fact that these parts receive a greater thickness of deposit than other por- tions of the article. The same observation applies to all projecting parts, and in order to remove the last traces of silver from such por- tions, when the silver has been dissolved from the main body of the work, the article should be raised out of the bath, and the projections or points dipped in separately, which will save the bulk of the article from being severely acted upon by the acid mixture. When the solution begins to work tardily, after a certain number of articles have been dipped in it, more saltpetre must be added from time to time, and the liquid kept well heated. Since oil of vitriol attracts moisture from the air. every time the bath is done with the vessel should be covered with a stout plate of glass. When a stripping bath has been much used, it works slowly, and the addition of saltpetre fails to invigorate it. When in this condi- tion a mass of crystals will deposit at the bottom of the vessel as the liquid cools. The bath must now be put aside and replaced by a fresh 468 OPEKATIONS CONNECTED WITH ELECTRO-DEPOSITION. mixture. The process for recovering the silver _from old stripping solutions is described at page 465. Cold Stripping Solution for Silver. A large quantity of strong sulphuric acid is poured into a sound and deep stoneware vessel ; to every two parts of the acid by measure one part of strong nitric acid (also by measure) is added, and the mixture is employed in its cold state. The process of stripping in this solution is much slower than in the former bath, and therefore requires less attention ; since, how- ever, the thickness of silver upon plated work varies considerably, from a mere film to a good stout coating, the progress of the work must be carefully watched from time to time, and the operator's judgment will soon guide him as to the quality of the plated work under treatment. The articles to be stripped are suspended from stout copper wires, or preferably by means of glass hooks, which may readily be formed from stout glass rods by simply bending them to the required form over an ordinary gas jet or Bunsen burner. It is very important that no water should be allowed to enter the stripping bath, otherwise the metal of which the articles may be com- posed, as brass, copper, German silver, &c., will be acted upon by the acid mixture. When the liquid begins to act tardily, after being worked for some time, a small quantity of strong nitric acid must be added, and this addition must be made whenever the liquid shows signs of weakness. When stripping silver from articles which have been plated, it is necessary to remove all the silver, otherwise, when the work is re- plated, the second coating may strip or peel off such parts as may have small portions of the old coating adhering to them. After the articles have been stripped, rinsed, and dried, they should be polished, or buffed, to render them uniformly smooth for replating, after which they are treated in the same way as new work preparatory to being placed in the depositing vat. Stripping Silver from Iron, Steel, Zinc, &c. Articles made from these metals, as also lead, Britannia, and pewter, must not be stripped in the acid stripping solutions, but the silver upon their surface may be removed by making them the anode in a cyanide of silver bath, and, as we have before suggested, it is better to keep a small bath for this special purpose than to risk injuring the usual plating bath by the introduction of other metals, which will surely occur when the silver is partially removed from the plated article by the solvent action of the cyanide. Stripping Silver by Battery. Make a strong solution of cyanide of potassium, say about one pound to the gallon of water. Attach the article to be deprived of its silver to the positive electrode of the battery or dynamo -electric machine, and suspend a strip of platinum STRIPPING NICKEL-PLATED ARTICLES. 469 foil to the negative electrode. When the bath has acquired a certain amount of silver (dissolved from the plated articles) the platinum will become coated, and if the current be powerful, the silver may become deposited in a granular state, and be liable to fall from the cathode in minute grains. To prevent these from falling to the bottom of the bath, the platinum cathode may be enclosed in a muslin bag, which by retaining the particles will enable them to be readily collected. A plate of gas carbon, German silver, or brass may be employed as a cathode instead of platinum, if desired. Stripping Gold from Silver Work. If done with great care, the gold may be readily dissolved from the surface of solid silver articles (not electro -plated) by means of warm aqua regia, composed of 4 parts of hydrochloric acid and I part nitric acid. The article may be either dipped in the aqua regia, or the acid may be applied to the article by pouring it over a part at a time, from a small porcelain ladle, and allowing the liquid to flow into the vessel containing the bulk of the acid. When this method is adopted, a vessel of clean water should stand by the side of the acid bath, in which the articles should be rinsed occasionally, and then allowed to drain before again applying the acid. The operation should be conducted over a sand bath, above which is a hood to conduct the fumes given off to the flue of the chimney. As we have hinted, the operation requires care, but if properly conducted it is expeditious. It may be as well to state that silver articles which have been mercury gilt probably more than once cannot be wholly deprived of their gold without injury to the article, for the reason that a considerable portion of the precious metal, in the primary stages of the amalgam process, becomes alloyed with the silver base. Electro -gilt silver articles, on the other hand, may readily be de- gilded, or stripped, by the above plan, or by making the articles an anode in a strong cyanide bath such as we have recommended for stripping silver, and employing an active current. To remove gold from silver articles by another method, they are first brought to a cherry-red heat, and then thrown into a weak solution of sulphuric acid, by which the gold scales off in spangles, and falls to the bottom of the vessel. The process of heating and plunging into the acid pickle is repeated until all the gold is removed ; after removing from the pickle each time, the article should be rubbed with a hard brush to remove any loosened particles of gold, and rinsed before being again heated. Stripping Nickel-plated Articles. Bearing in mind what we have urged, that nickel will not adhere to a nickel-plated surface, it is necessary to remove the old nickel coating from all articles which have to be re-covered with this metal. In the case of German, French, and American* nickel -plated articles which are largely imported into 4/O OPEEATIONS CONNECTED WITH ELECTKO-DEPOSITION. tliis country, the removal of the nickel coating is by no means a troublesome task ; trifling though the film may be, however, as, in- deed, it frequently is, the film must be removed before any attempt is made to replate the article, otherwise the new coating will assuredly strip from the old one during the process of finishing, if not while it is in the bath. The stripping acid, which may be used either cold or tepid, is composed of : strong sulphuric acid, 4 Ibs. ; nitric acid, I Ib. ; water, about i pint. The water should first be put into a stoneware jar, and the sulphuric acid added cautiously and a little at a time, since consi- derable heat is generated when this acid is mixed with water. When the entire quantity of sulphuric acid is added, the nitric acid is then to be poured in, when the bath is ready for use. In making up the stripping bath, the proportion of the acids may be varied, but the foregoing will be found to answer every purpose. When stripping nickel -plated articles in the above bath, it is neces- sary to watch the operation attentively, since, as we have observed, some articles are very lightly coated, and a momentary dip is fre- quently sufficient to deprive them of their nickel. Other articles which having been thoroughly well nickeled require, from some accidental cause, to be stripped and re-nickeled, will need immersion for several minutes indeed, we have known well-nickeled articles to occupy nearly half an hour in stripping before the underlying brass surface has been entirely free from nickel. The operation of stripping should be conducted in the open air, or in a fire-place, so that the acid fumes, which are very pernicious, should escape freely. The articles should be attached to a stout copper wire, and after a few moments' immer- sion should be removed from the bath occasionally, to ascertain how the. stripping progresses, and the moment it is found that the nickel has quite disappeared from every part, the article must be plunged into clean cold water. It is absolutely necessary that the work should not remain in the stripping solution one instant after the nickel is re- moved. When the stripping has been properly effected, the under- lying metal exhibits a bright, smooth surface, giving little evidence of the mixture having acted upon it. Nickel may be stripped from brass and copper articles, by electro- lysis, in a dilute solution of sulphuric acid, making the article an anode, as in other arrangements of a similar kind ; or a small nickel bath may be kept specially for this purpose. Stopping-off. This term is applied to various methods of protect- ing certain parts of an ornamental article which are required to be part gilt and part silvered, or otherwise varied, according to taste. For this * We allude only to imported articles ; doubtless those retained in these countries for home use are, like our own, better treated. STOPPING-OFF. 47 1 purpose, certain varnishes, called "stopping-off" varnishes, or " stopping," are employed. The materials vary in their composition according to whether they have to be used with hot or cold solutions, more especially when cyanide of potassium is the active ingredient in the depositing bath. A formula which has, with modifications, been much employed for protecting plated work, to be gilt in the hot cyanide bath, from receiving the gold deposit upon certain ornamental parts of the work, is composed of Clear resin ...... 10 parts. Yellow beeswax . . . . 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, forms 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, arid 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 47 2 OPEEATIONS 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 -r 6 -th of an inch. The ring was immersed in a solution of sulphate of copper, and at the ELECTROLYTIC 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^thecohesiveness 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 Regia. 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. Eor 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 47^ MATEKIALS USED IN ELECTRO-DEPOSITION. 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 : Reduce 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. 477 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 in 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 ferrocyanide 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 478 MATERIALS USED IN ELECTRO-DEPOSITION. 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- dientj 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 CYANIDE OF POTASSIUM. 479 of insoluble impurities which cause this greyness will readily subside wheu 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 in 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- * Ammonia-sulphate of copper is formed by adding liquid ammonia to a saturated solution of the sulphate until the precipitate at first produced is redissolved, 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 100 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 grains 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 Prussic 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 J 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. IVickel 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 great 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 doiible 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-DEPOSITION. 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 Slack 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. Pyrophosphate of Soda. This salt, which has been much used, especially in Prance, 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 f ailing 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 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 times 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. 40 USEFUL INFOEMATION. 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, thejfcs^ 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 usmg driving belts, may be unacquainted with the principles of their action. Chutter's Dynamo-electric Machine. Since the earlier portion CHUTTEE'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- i33- \ horse -power, will, under favourable conditions, deposit about 20 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, 1 7 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 heating, 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 pj 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. II T7 i 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 charge extra insurance where gas-engines are employed. Mr. F. T. Linton, of the Leith G-as Works, in a paper upon this subject,* says, in reference to a 3-3- horse-power " Otto " engine, which had been adopted at the works: "It is employed to drive various machines in our workshops, such as Root's blower for three smiths' fires, a large screw -cutting lathe, a screwing machine, a drilling Fig. 135- 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 INFORMATION. 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 attaching 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 battery . . 104 grains. Deposited Smee battery . . 22 grains. Wollaston . .18. Single-cell apparatus . 62 Daniell battery . . 33 Constancy of Batteries. The action of most batteries differs after RELATIVE INTENSITY OF 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 3ii Daniell 33 35 34 32 32 30 3i 227 Smee . 22 16 14 II 12 ii 10 96 Wollaston . 18 14 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 . 19 J 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 thfs 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 Two inches . 8' 8 grains. 6-6 12*0 grains. 6-8 31-0 grains. 26-0 Three 47 6-0 1 7' 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 four-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 Fig> I37 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 are supplied by Mr. Carlyle, of Birmingham, at a moderate price, and may be had to indicate up to 1,000 revolu- K K 498 USEFUL INFOKMATioN. 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. Fig. 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. Ductility. 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 5OO USEFUL INFORMATION. silver from nitrate of silver, the equivalent of which is 170. The test solution, therefore, is prepkred from pure nitrate of silver, 8172 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 in 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 100 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 grains in this way, a permanent faint cloudiness is produced, the sample contains 52 per cent, of real cyanide. If the original test solution is preferred, 1,000 grains of that to be tested must be used, and the result is the same." Oxidising Copper Surfaces. To produce a deep black coloration upon a cleaned 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. ( lire.} 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, as illustrated in the following table : ALLOYS HAVING A DENSITY Greater than the mean of their constituents. Copper and bismuth. ,, palladium. tin. ,, zinc. Gold and antimony. , , bismuth. , , cobalt. ,, tin. ,, zinc. Lead and antimony. Palladium and bismuth. Platinum and molybdenum. Silver and antimony. ,, bismuth. lead. ,, tin. zinc. Less than the mean of their constituents. G-old and copper. , , iridium. ,, iron. . lead. ,, nickel. , , silver. Iron and antimony. , , bismuth. lead. Nickel and arsenic. Silver and copper. Tin and antimony. lead. ,, palladium. Zinc and antimony. 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 versa, 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 to the colour and standard required. It appears that the best proportion of metals to form fine brass is one prime equivalent of copper = 63^ -Jf- 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 . . -j|r. . Copper and zinc. Britannia metal . . . Tin, with antimony, copper, and 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 ^lloy 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 . 5O4 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, 12; zinc, 6 parts; tin, i part, melted together. JBrass 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 may be, 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. 5O8 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 EEMEDIES. 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 mula, quickly 5IO USEFUL INFORMATION. induced vomiting ; copious doses of warm water, assisted by again irritating the trnda, 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 513 USEFUL TABLES. TABLE I. ELEMENTS, THEIR SYMBOLS AND ATOMIC WEIGHTS. Name. I Atomic Weight. ; Name. 2 g Atomic Weight. Vj. . 00 Aluminium . Al. 27*5 Mercury Hg. 200 " Antimony . Sb, 122' Molybdenum Mo. 96- Arsenic As. 75' Nickel . Ni. 59' Barium Ba. 137' Niobium Nb. 97-5 Bismuth Bi. 210' Nitrogen N. 14' Boron . B. io - 9 Osmium Os. 199- Bromine Cadmium Br. Cd. 80- 112' Oxygen Palladium 0. Pd. i6'# io6'5 Caesium OB, 133- Phosphorus P. 3i' 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. 28- JDidymium . D. 96- Silver . A g- 108- Erbium E. (?) Sodium. Na. 23- Fluorine F. 19- Strontium Sr. 37'5 Gallium Sulphur S. 32' Glucinum . G. 9'3 Tantalum Ta. 138- Gold . Au. 196-6 Tellurium Te. 129' Hydrogen H. I* Thallium Tl. 204- Indium In. Ii3'4 Thorinum Th. 119- Iodine . I. 127* Tin . Sn. US' Indium Ir. 197- Titanium Ti. 50' Iron Fe. 56" Tungsten w. 184' Lanthanum . La. 92' Uranium U. 120' Lead . Pb. 207' Vanadium V. !37' Lithium L. r Yttrium Y. (?) Magnesium . Mg. 24'3 Zinc . Zn. 65- Manganese . Mn. 55* Zirconium Zr. 89-5 ; * The combining weight of oxygen is 8. USEFUL TABLES. TABLE II. RELATIVE CONDUCTIVITY OF METALS. By L. WELLLKR. Xames of Metals. Conduc- tivity. Observations. i. Silver, pure 2. Copper, pure 3. Copper, pure super refined and crystallised 4. Silicium bronze (telegraphic) 5. Copper and silver alloy at 50 per cent. 100- IOO- 99'9 98- 86-65 78- These experiments have been conducted with u series of bars especially prepared for the pur- pose. These said bars have been molten at a uniform diameter of about 13 mil- 7. Silicic copper (with 4 per cent, of silicon) 8. Silicic copper (with 12 per cent, of 75" 54'7 limetres. They have been cut so as to show the grain of the metal, and the detached portions 9. Aluminium, pure .... 10. Tin, containing 12 per cent, of sodium ii. Silicium bronze (telephonic) . 12. Plombiferous copper, with 10 per cent, of lead .... 13. Zinc, pure ..... 14. Phosphor bronze (telephonic) . 15. Silicious brass, with 25 per cent, of zinc 16. Brass, with 35 per cent, of zinc 17. Phosphide of tin 1 8. Gold and silver alloy, 50 per cent. . 54'2 46-9 35- 30- 29-9 29- 26-49 21-15 17-7 l6'I2 1 6- have then been drawn into wires. It is on the wires so obtained that the said experiments have been carried out, and of which the results are given in the table. As regards those alloys which can neither easily be drawn nor rolled, such as certain phosphides or silicides, the measure - ments have been taken 20. Pure tin of Banca ..... I5-45 12-7 direct from the bars ac- cording to the method of 22. Aluminium bronze, 10 per cent. 23. Siemens' steel 24. Platinum, pure 25. Amalgam of cadmium, with 15 per cent, of cadmium 26. Mercurial bronze, Drosnier 27. Arsenical copper, with 10 per cent, of arsenic ..... 28. Lead, pure , 29. Bronze, with 20 per cent, of tin 30. Nickel, pure 31. Phosphor bronze, with 10 per cent. 12-6 12- io'6 I2"2 IO-I4 9'I 8-88 8-4 7-89 6-s Sir W. Thomson. The measurements have been taken by means of a Wheatstone bridge with a sliding index, a diffe- rential galvanometer and a battery of four cells. 32. Phosphide of copper, with 9 per cent, of phosphorus .... 33. Antimony 4'Q 3-88 USEFUL TABLES. 5'5 TABLE III. SPECIFIC RESISTANCE OF SOLUTIONS OF SULPHATE OF COPPER. Bv FLEEMTNG JENKIN. Sulphate of copper. Temperature. Fahrenheit. 57 61 64 68 3 75 82 86 Water. 8 parts. 100 parts. 457 43'7 41-9 40-2 37*1 34'2 32-9 12 100 36-3 34'9 33'5 32-2 29-9 27-9 27-0 16 100 31-2 30-0 28-9 27-9 26-1 246 24-0 20 100 28-5 27'5 26-5 2^6 24'I 22-7 22'2 24 100 26-9 25'9 24-8 23'9 22*2 20-7 2O'O 28 100 247 23'4 22*1 2I'O 1 8-8 16-9 l6'o TABLE IV. SPECIFIC RESISTANCE OF SOLUTIONS OF SULPHATE OF COPPER AT 500 FAHR. By EWING and MACGREGOB. Density. Specific resistance. Density. Specific resistance. 1-0167 1-644 1-1386 35'0 I'02i6 1*348 1-1432 34'i i '03 1 8 9-87 1-1679 . 3i'7 I '0622 5'90 1-1823 30*6 1-0858 4'73 1-2051 (satu- 29'3 1-1174 3'8i rated). TABLE V. TABLE OF HIGH TEMPERATURES. Degrees. Fahr. Description. D ffhr?' j Description. 977 980 100^ 1140 1 200 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 330Q 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. 1 Fahr. Cent. Fahr. Degrees. Degrees. Degrees. Degrees. Degrees. Degrees. o 32 33 91-4 67 152*6 i 33'8 34 93-2 68 54'4 2 35-6 35 95 69 156-3 3 37'4 36 96-8 70 158 4 39-2 37 98-6 71 i59'8 5 41 38 100-4 72 i6r6 6 42-8 39 IO2"2 73 i63'4 7 44-6 40 104 74 165-2 8 46-4 4i 105-8 75 167 9 48-2 42 107-6 76 1 68-8 10 50 43 109-4 77 170-6 ii SI'S 44 lira 78 172-4 12 53-6 45 113 79 174-2 13 55-4 46 114-8 80 176 14 57'2 47 116-6 81 177-8 15 59 48 118-4 82 179.6 16 60-8 49 I20'2 83 181-4 i? 62-6 50 122 84 183-2 18 64-4 51 123-8 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' 71-6 55 131 89 192*2 23 73*4 56 132-8 90 194 24 75*2 57 1 34' 6 9i I95'8 25 77 58 136-4 92 197-6 26 78-8 59 138-2 93 199-4 27 80-6 60 140 94 201'2 28 82-4 61 141-8 95 203 29 84-2 62 I43'6 96 204-8 30 86 63 I45-4 97 206-6 31 87-8 64 I47'2 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. Weight per Square Weight per Square ' Thick- ness by B.W.G. Diameter in Inches. Foot. Thick- ness by B.W.G. Diameter in Inches. Foot. Sheet Sheet Sheet Sheet Copper. Lead. Copper. Lead. No. inch. Ibs. Ibs. No. inch. Ibs. Ibs. oooo '454 20-566 26-75 19 '042 1-93 2-48 ooo 425 19-252 25*06 20 035 61 2*04 oo 380 17-214 22-42 21 032 47 89 o 340 15-6 20-06 22 028 29 65 I 300 13*8 17-72 23 025 "14 '47 2 284 13" 16*75 24 '022 'OI 30 3 259 11-9 15*26 25 '020 918 1-18 4 238 II' 14-02 26 018 826 06 5 220 1C' I 12-98 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 9-73 30 'OI2 '551 708 9 148 6-8 8-72 31 'OIO 480 600 10 134 6'l6 7-90 32 009 420 532 ii 120 S'5 1 7-08 33 OO8 370 472 12 109 5'02 6-42 34 OO7 323 413 13 095 4"37 5'6o 35 005 262 309 14 -083 4-90 36 004 194 236 15 -072 3-31 4' 2 5 16 065 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. 7/0 500 13 092 32 0108 6/0 464 14 080 33 'OIOO 5/o '432 15 072 34 0092 4/0 400 16 064 35 0084 3/o 372 17 056 36 0076 2/O 348 18 "048 37 0068 '324 19 040 38 0060 I 300 20 036 39 0052 2 276 21 032 40 0048 3 252 22 '028 41 0044 4 232 23 024 42 0040 5 '212 24 '022 43 0036 6 192 25 *02O 44 0032 7 I 7 6 26 018 45 0028 8 160 27 0164 46 0024 9 144 28 0148 47 'OO20 10 128 29 0136 48 '0016 ii 116 30 0124 49 *OOI2 12 104 31 0116 50 '0010 ;1 5'S USEFUL TABLES. IX.-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' equals . . WEIGHT. TEOY WEIGHT. equals IMPERIAL MEASURE. eqtwh ... 1 6 ounces. 8 drs. (480 grains).* 3 scruples. 2 grains. 12 ounces. 20 pennyweights (d \vts . ), or 480 grains.* 24 grains. 8 pints. 20 ounces. 8 drachms. 60 minims. FRENCH on METRICAL SYSTEM. French If 'eight. Kilogramme, 1,000 grammes . equal* . 2 Ibs. 3|- ozs. nearly. Gramme (the unit) 15-432 grains. French Measure of Volume. I litre (the unit) . . . equals . 34 fluid ounces near Long Measure. Metre (the unit) . . . equals . Decimetre (roth of a metre) . ,, Centimetre ( i ooth of a metre) . Millimetre (loooth of a metre) . ,, 39-371 inches. 3-937I 0-3937 -393 * An ounce Avoirdupois is only 437-5 graii WORKS RELATING TO ELECTRO -DEPOSITION. GALVANOPLASTIC ART. M. H. Jacobi. Translated by "VV. Stur- geon. 1841. ELECTROTYPING, MEMOIR ON. F. Zantedeschi. Venice. 1841. ELECTRO -PLATING OF GOLD AND SILVER APPLIED TO HOROLOGY. A. O. Mathey. Paris. 1855. ART OF ELECTRO-PLATING. C. H. Schmidt. 2nd Edition. Weimar. 1855. ELECTRO - CHEMICAL PROCESSES FOR GOLD, ETC., PLATING. Perrot. Paris. 1845. ELEMENTS OF ELECTRO-METALLURGY. Alfred Srnee. 3rd Edition. 1851. ELECTRO -GILDING AND SILVERING. W. Sturgeon. 2nd Edition. 1843. MANUAL OF ELECTRO -METALLURGY. George Shaw. 2nd Edition. 1844. CONTRIBUTIONS TOWARDS THE HISTORY OF ELECTRO - METALLURGY. H. Dircks. 1844. ELECTROTYPE MANIPULATION. C. Vincent Walker. Part I., 29th Edi- tion. 1859. Part II., i6th Edition. GALVANOPLASTIE. ENCYCLOPEDIE-RORET. 2 vols. Paris. 1854. GILDING AND SILVERING BY ELECTRO -DEPOSITION. F. Selmi and others. 1856. ELECTROTYPINQ AND ELECTRO-PLATING. A. G. Martin. Vienna. 1856. THEORY AND PRACTICE OF ELECTRO-DEPOSITION. G. Gore. 1856. REPERTORIUM DER GALVANOPLASTIK UND GALVANOSTEGIE. A. Martin. 2 vols. Vienna. 1856. HISTORY OF ELECTRO -METALLURGY. Henry Dircks. 1863. ELEMENTS D'ELECTRO-CHEMIE. M. Becquerel. Paris. 1864. KATECHISMUS DER GALVANOPLASTIK. F. Martins Matzdorff . Leipzig. 1868. ELECTRO -DEPOSITION OF COPPER AND BRASS. W. H. Walenn. 1870. ELECTRO-CHEMICAL RESEARCHES. E. Fremy and A. E. Becquerel. Paris. 1852. SCIENTIFIC RESEARCHES IN ELECTRO-CHEMISTRY. W. Sturgeon. 1850. ELECTRO-CHEMISTRY WITH POSITIVE RESULTS. C. Chalmers. 1858. HANDBUCH DER GALVANOPLASTIK. Dr. F. Binder. Weimar. 1884. GALVANOPLASTIC MANIPULATIONS. A. Roseleur. Philadelphia. 1872. MANUAL OF ELECTRO -METALLURGY. J. Napier. 5th Edition. 1876. ART OF ELECTRO-METALLURGY. Geoi'ge Gore, LL.D. 2nd Edition. 1884. 520 WORKS RELATING TO ELECTRO-DEPOSITION. ELECTRO -PLATING. J. W. Vrquhart. 1880. ELECTROTYPING. J. W. Urquhart. 1881. ELECTRO -METALLURGY PRACTICALLY TREATED. Alexander Watt. 8th Edition. 1882. ELECTROLYSE, GALVANOPLASTIK UND REINMETALLGEWINNUXG. E. Japing. Leipzig. 1883. GrALVANOPLASTic MANIPULATIONS. H. Wahl. Philadelphia. 1884. ELECTROLYSE, BENSEIGNEMENTS PRATIQITES SUR LE NICKELAGE, &c. 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 ; Spot'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 Neivs; Timmins' Midland Hardware District, 1866 ; Bevan's "British Manufacturing Industries," 1876; Encyclopaedia Britan- nica, vol. viii., 1878; Dinglfr's Polytechnic Journal; Elcktrotcchuixche ZcitKfJirifl. Berlin. INDEX. 1 CCOUTREMENT, army, gilding, ^ 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 and ammonium, chlo- ride of, 363 bronze, 448, 514 deposition of, 360 deposition of, Goze's process, 363 522 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 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,. 319 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. 523 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 alloys, 390 cobalt, 351 copper, 144 dirty, 278 gas carbon, 343 ., gold, worn, 211 iron, 341, 397 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 Antimcniate 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, 47 6 regia, 195, 47 6 Argentiferous copper pyrites, 436 galena, 435 Argol, 238 Argyrometric scale, Koseleur's, 262 Armature, 22 intensity, 25 quantity, 25 Army accoutrement work, gilding, 185 Arrangement of baths for electro- lytic refining, 427 ,, of battery, no for coppering hydraulic rams, 144 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 DABBINGTON'S battery, 7 Bacco's brassing solution, 376 Backing pan, 133 -up metal, 133 Balance, plating, 261 524 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, 377 ,, cold gilding, observations on, 174 ., dust on the surface of, 278 electrotyping, 132 . for gilding steel, 186 J 77 Record's, 176 gold, management of, 21 1 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 n 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, t> 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 Plante's 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, no constant, 51 ,, constancy of, 494 electrotyping, 132 electromotive force of, SS ,. 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 Becquerel's process for treating gold, 2 34 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 T)AMASCENING, 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 Dechaud 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, 378 Deposition of an alloy of tin and silver, 389 aluminium, 360 aluminium, Goze's process, 363 aluminium, Jeancon's process, 363 ., aluminium, Thomas and Tilley'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 f ., chromium, 364 chromium alloys, Sla- ter's process, 390 cobalt, 351 copper by dynamo- electricity, 139 copper on iron, 141 copper by single cell, 91 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, Jacob! and Klein's process, 342 lead, 357 534 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 platinum by single immersion, 350 silicon, 365 by simple immersion, 230 of tin, 331 tin by dipping, or sim- ple immersion, 331 tin by single cell pro- cess, 334 De Ruolz's gold solution, 172 De-silvering, 253 Desmur's solution for nickeling small articles, 299 Dials, brass clock, 403 magneto, 21 negative, 2 positive, 2 quantity of, and electro- motive force, 490 refining copper by, M. Th^nard'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 INDEX. Electro-brassing wrought-iron work, 380 zinc work, 380 Electro bronzes, 192 chemical action, 4 chemical action, Faraday's nomenclature of, 70 ,, chemical decomposition, 358 V, chlorination of gold ores, Cassel's process, 438 coppering flowers, insects, &c., 118 ' deposited gold, colour of, 196 deposited silver, thickness of, 265 Electro-deposition of alloys, 366, 379 aluminium, 360 antimony, 355 auxiliary ope- rations con- nected with, 466 bismuth, 355 ?, brass, 366 bronze, 366, 388 cadmium, 363 chromium, 364, 390 cobalt, 351 copper, 91 ,, German silver, 388 German silver Morris and Johnson's pro- cess, 389 historical re- view of, 51 iron and zinc, 340 lead, 357 ,, magnesium,365 manganese, 365 ,, manganium, 365 materials used in, 475 Electro-deposition of nickel, 280 palladium, 354 ., platinum, 348 platinum by battery cur- rent, 350 ,, platinum, Bo- ettger's solu- tion, 351 , , platinum by simple immer- sion, 350 silicon, 365 silver, 219 tin, 331 ,, various metals, 348 zinc, Watt's so- lution for, 345 Electro-etching, 151 composition of bath for, 152 Electro-gilding, general manipula- tions of, 177 or gilding by direct current, 166 ,, solutions, cold, 172 zinc articles, 192 Electro-gilt work, burnishing, 460 Electro-magnetism, 18 Electro-magnets, 21 Electro-metallurgy, 61, 395 of copper, Dr. C. W. Siemens on, 401 zinc, 439 Le- trange's pro- cess, 439 zii;c,Luckow's process, 441 zinc, MM. Bias and Meist's process, 442 ,, Werdermann's process, 443 Electromotive force, 28, 82, 399 INDEX. 537 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, 32 1 handrails, &c., 312 harness furniture, 316 long pieces of workj 312 mullers,&c., 309 printing-rollers, 321 purse mounts, &c , 322 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, &c., 313 sword - scabbards, table lamps, &c.,3o8 Electro-plate, 251 characteristics of, 259 resilvering, 258 Electro-plated articles, whitening, 267 articles, stripping silver from, 259 Electro-plating, 219 bath, arrangement of, 241 battery, 242 ,, brass, &c., 250 ,, Britannia metal, &c., 250 ,, cruet stands, &c., 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 Koseleur'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, 406 538 INDEX. Electrolysis, Mr. B. N. S. Keith on re- fining copper by, 401 recovery of tin from tin scrap by, 338 of sulphate of copper, 75 of sulphate of potash, &c., 76 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, 42 ij Electrolytic treatment of natural sul- phides, 441 treatment of ores, 434 zinc as a printing surf ace, 346 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> 133 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, &c., 140 depositing bath, 132 floating moulds in, 1 1 8 guiding wires for, 113 ,, Knight's plumbagoing process for, 129 leaves, ferns, fishes 66., 1x5 Lenoir's process for, 140 metallising the moulds in, 130 moulding case for, 126 moulding composition for, 125 INDEX. 539 Electrotyping, moulding materials used in, 94 moulds from fusible metal for, 108 non-metallic substan- ces, 120 plants and seaweed, 120 from plaster moulds, 136 pluuibagoing machine used in, 129 power of current re- quired in, 132 printers' set-up type, 123 removal of air bubbles in, 93 ., Schlumberger's pro- cess for, 142 by separate battery, no by the single-cell pro- cess 91 tin powder for, 138 wood engravings, &c., 136 Elements, electrical transfer of, 77 electro-negative, 89 electro-positive, 89 their symbols and atomic weights, 513 Elkington's, G. K., gilding process, 158 Elkington's, J. B., process for refining copper by electrolysis, 400 coppering solution, 148 Eisner's experiments in the electro- soldering of copper, 72 process for oxidising, 271 Emery, 449 cloth, 1 80, 257 powder, 455 wheel, 455 wheels, 249 Employment of impure gold, 209 Enamel, black, 273 Enamelled iron pans for gilding baths, 187 End-brush, 183 Engraved copper-plates, facing, 340 metal plates, copying and facing with iron, 342 Erbium, 513 Etching, electro, 151 ground composition, 151 voltaic, 151 Ether, sulphuric, 187, 342 ~ Evaporation of mercury, 204 of old gold solutions, 211 Evolution of hydrogen during depo- sition, 393 Excess of cyanide, 275 injurious, 216 Experiments, Dr, Golding Bird's, 62 Gramme's, with sulphate of copper baths, 411 Sir H. Bessemer's, 60 Sir H. Davy's, on the transfer of elements, 77 External resistance, 85 Extraction of silver by the dry me- thod, 464 by the wet me- thod, 463 "PACING engraved copper-plates, 340 Facing, nickel, electrotypes, 320 Fancy gilding, 196 work, cheap, nickeling, 306 Faraday's nomenclature of electro- chemical action, 70 Fearn's tinning process, 336 Felt, 452 Fender and stove work, brassing, 392 Fenders, iron, bronzing, 384, 387 Ferrate of potassium, 341 Ferrocyanide gilding solution, 175 of iron solution, Boett- ger's, 344 of potassium, 168, 341, 481 540 INDEX. Filigree work, gilding, 184, 210 gilding solution for, 185 Filling the case (electrotyping), 126 Filtering-paper, 172 Finishing, brass, 451, 454 or colouring, 457 dolly, 454 the electrotype, 134 hand, 457 lime, 454 mop, 457 stone, 460 Fixing the belt, 488 Fizeau's solution for gilding, 169 Floating moulds, 118 Flowers, insects, &c., electro-copper- ing, 118 Fluorine, 513 Foil, platinum, 469 silver, 508 Foot-lathe, for polishing, 456 Forceps, &c., nickeling, 323 Fork and spoon work, plating, 238 Forks and spoons, scratch -brushing, 248 plating by weight, 265 ., stripping, 467 wiring for plat- ing, 239 Forme, plumbagoing the, 125 Formes, preparing the, 124 Foxy colour in gilding, 181 Frames, purse, &c., nickeling, 306 Free cyanide, 184, 223 test for, 499 French and English thermometer scales, comparative, 516 French cheap goods, re-nickeling, 319 gilding for cheap jewellery, 1 60 gilding solutions, 169 jewellery, gilding, 212 method of bronzing electro- brassed zinc work, 386 verdigris, 198 French wet colouring, 201 Frosted gilding, 180 Fulminate of gold, 211 Fulminating gold, 172 Fumes, acid, 493 Fuming nitric acid, 236, 481 Furnace, Cowles' electric smelting, 445 Fused sulphur, 273 Fusible metal, 96, 503 moulds from, 108 /1ALENA anode, 442 ,, argentiferous, 435 Gallium, 513 Galvanic battery, i batteries, 2 engraving in relief/52 Galvani's discovery, 2 Galvanising iron, 345 Galvanism, i Galvanometer, 19, 39 scales, whitening, 231 Gas bubbles, removing, 322 carbon, 12 anodes, 343 engines, advantages of, in driv- ing dynamo machines, 491 sulphurous acid, 397 Gassiot and Crosse's water battery, 15 Gauze wire, nickeling, 321 Gelatine, 342 General manipulations of electro- gilding, 177 General treatment in cases of poison- ing, 5io German cheap goods, re-nickeling, 3i9 silver, 388 silver anode, 389 silver, deposition of, Morris and Johnson's process,389 silver, deposition of, Watt's method, 388 silver gilding, 171, 186,213 silver, temperature of solu- tion for gilding, 186 INDEX. 541 German silver, plating, 250 ,, silver solution, 388 Gilders' wax, 207, 208 Gilding Albert chains, 177, 208 amalgam, 202 army accoutrement work, 1 85 bath, 170, 177 Record's, 176 for steel, 186 baths, management of, 211 Becquerel's solution for, 168 | brass and copper, solution j for, 159 bright and dead in parts, 205 j ,, Britannia metal, 167 ,, bronze, solution for, 160 ,, bronzes with amalgam, 206 brooches, 177, 208 ,, by Bunsen's battery, 178 causes which affect the co- lour of, 181 chains," 208 chalices, 187 ,, cheap jewellery, 212 ,, chloride of gold solution for, 187 ,, clock cases, 195 ,, clocks, 163 cold, 195 in cold baths, observations on, 174 ,, colour of deposit in, 196 colouring processes for im- perfect, 198 ,, by contact with zinc, Steele's process, 164 with copper anode, 213 ,, cream ewers, insides of, 183 ,, ,, goblets, &c., 211 ,, by Daniell's battery, 177 dead, 180 ,, defective, colouring mixture for, 198 ,, defects in, 212 ,, De Ruolz's solution for, 172 ,, different metals, 209 Gilding by direct current, or electro- gilding, 1 66 ,, the " doctor " used in, 184 ,, doctoring, 165 ,, dry-colouring, mixture for inferior, 199 ,, electro, 166 ,, electro, general manipula- tions of, 177 ,, electro, solutions, cold, 172 ,, ,, zinc articles, 192 ,, employment of impure gold in, 209 ,, excess of cyanide injurious in, 216 ,, fancy, 196 ,, filigree work, 184, 210 ,, Fizeau's solution for, 169 ,, foxy colour in, 181 ,, French, for cheap jewellery, 160 French jewellery, 212 ,, solutions for, 169 ,, frosted, 180 ,, German silver, 171, 186, 213 ,, gold articles, 183 ,, green gold colour, 197 , , by immersion in an ethereal solution of gold, 159 ,, by immersion in a solution of chloride of gold, 159 insides of vessels, 183 jewellery articles, 208 ,, lead, Britannia metal, Ac., 216 ,, lockets, 177, 179 ,, matted or dead, 185 ,, M. de Briant's solution for, 169 ,, mercurial, injurious effects of, 185 ,, mercury, 202 ., M dip for, 180 ,, metal, 180, 503 ,, ,, chains, 180 ,, metals with gold leaf, 195 ,, mounts, 184 542 INDEX. Gilding, moving the anode in, 183 mugs, 183 ,, mystery gold, 213 ,, notes on, 208 ,, old, solutions, treatment of, 210 ,, ornamental, 197 ,, ,, bronzes, 163 ,, a pale straw colour. 198 ,, patens, 187 ,, pewter solder, 212 ,, pink gold colour, 198 ,, with platinum anode, 187 with platinum wire anode, 178 ,, pot, 162 ,, preparation of work for, 164, 179 ,, preparation of zinc castings for, 192 , pyro, 196 ,, with the rag, 165 , Kecord's, solution, 176 ,, red gold colour, 197 ,, rings, 177, 208 ,, scabbards, 185 scarf pins, 177, 208 ,, scratch-brushes used in, 178, 179 ,, silk, cotton, &c., 195 ,, silver by dipping, 164 ,, . silver filigree work, 184 ,, silver filigree work, solution for, 185 ,, silver, solution for, 159 ,, by simple immersion, 159 ,, slinging wires used in, 179, 215 ,, small articles, simple ar- rangement for, 177 ,, by Smee's battery, 181 ; snuff boxes, 165 solution, ferrocyanide, 175 ,, ,, heating the, 178 ,, Record's, 176 ,, for silver filigree work, 185 Gilding solution, Watt's, 176 ,, solutions, 215 ,, solutions, making, by bat- tery process, 171 solutions, preparation of, 167 ,, ,, treatment of, 208 ,, spoons, 165 ,, spurious gold, 213 steel, 1 86 ,, steel articles, preparation of the work, 187 ,, steel, composition of bath for, 186 ,, steel pens, 188 ,, stone, 203 ,, sugar basins, 183 , , superior conductivity of hot solutions for, 166 ,, sword mounts, 185 ,, tankards, mugs, &c., 210 time-pieces, 187 in various colours, 196 ,, wash, 202 ,, watch cases, 177 ,, watch chains, 179 ,, watch dials, 214 ,, watch movements, Conti- nental method of, 188 watch movements, Pinaire's method, 188 ,, water, 158, 202 with Wollaston battery, 181 ,, Wood's solution for, 169 ,, zinc articles, Continental method of, 193 Gilt work, colouring, 162, 198 Glass-cutters' sand, 452, 486 Glass, porcelain, &c., depositing cop- per upon, 1 20 Glauber's salt, 225 Glucinum, 513 Glucose, 350 Glyphography, 152 Goblets, cream ewers, &c., gilding, 211 Gold, 159, 503, 514 INDEX. 543 Gold, amalgam, 203 ,, ammoniuret of, 172 ,, anode, 171, 183 ,, anodes, worn, 211 articles, gilding, ,, ,, recolouring, 199 ,, baths, management of, 211 ,, chloride of, 187, 477 ,, chloride of, preparation of, 157 ,, chloride of, gilding by immer- sion in solution of, 159 ,, coloured, 183 colour, red, 206 cyanide of, 167, 461 ,, double cyanide of, cry itallised, 462 ,, ethereal solution of, 159 ,, fulminate of, 211 ,, fulminating, 172 green, 197 impure, employment of, 209 leaf, gilding metals with, 195 and mercury, amalgam of, 185 mosaic, 503 mystery, 213 old, 209 standard, 503 ores, electro-chlorination of, Cassel's process, 438 pale straw-coloured, 198 pink, 198 and potassium, double cyanide of, 167 red, 197 silver, and copper ores, Bec- querel's process for treating, 434 and silver alloys, deposition of, 390 and silver, recovery of, from scratch-brush waste, 464 and silver, recovery of, from old cyanide solutions, 461 and silver ores, Lambert's pro- cess of treating, 437 and silver, pyroplating with, 266 Gold and silver, recovery of, from old stripping solutions, 465 and silver work, to remove soft solder from, 507 size, 121 solution for giving a stout coat- ing, 215 solution, making the, 167 solution for producing dead or matted surfaces, 215 solutions, old, 210 strengthening, 173 spurious, 213 standard, 503 stripping, from insides of plated articles, 256 stripping, from silver, 213, 469 terchloride of, 157, 439 Goze's process for deposition of alu- minium, 363 Grain gold, 167 silver, 219 tin, 331, 332 Graining watch movements, i89 ? 190 powders, 189 Gramme's experiments with sulphate of copper baths, 411 magneto-electric machine, 27 Granular charcoal, 447 Granulated carbon, 445 zinc, 333 Granulation, 209 Graphite, 11,329,484 battery, Walker's, 13 Ceylon, 128 crystalline, 449 Greek fire, 119,485 Green or antique bronze, 386 bronze, 385 colour, 392 copperas, 340 gold, 197 vitriol, 485 Grey cyanide, 479 Grove's battery, 10 544 INDEX. Grove battery, compound, 1 1 Guiding wires, 113 Gulcher's dynamo-electric machine, 37 Gulensohn's process for coppering, 149 Gun barrels, browning, 357 Gutta-percha, 94 baths, 472 lining for plating tanks, 279 and marine glue, 95 moulds, 264 plastic, 95 tubing, 237 Gypsum, 77 TTAIR, hog, brushes, 303 - Hallett-Elmore machine, 33 Hand finishing, or colouring, 457 polishing, 257 rails, &c., nickeling, 312 shaving machine, 135 Hard solder, 503 soldering, 504 Harness furniture, nickeling, 316 Heating gilding solutions, 178 Heeren's method, of tinning iron, 334 Dr., [process for brassing, 373 Hematite, 206 Hercules alloy, 448 Hermann's zinc process, 347 Hessian crucible, 463 Higgs', Dr., observations on refin- ing copper by electrolysis, 406 Hillier's, Dr., method of tinning metals, 334 Hippopotamus hide for polishing bobs, 452 Historical review of electro-deposi- tion, 51 of voltaic electri- city, i Hoe's electric connection gripper, 130 Hog-hair brushes, 303 Holding the parts in gilding watch movements, 189 Holes, sand, 330 Hooks, eyes, buttons, &c., whitening, 230 Horse-shoe magnets, 21 Hot solutions, brassing in, 394 Hydrated chloride of cobalt, 353 oxide of nickel, 297 Hydraulic rams, arrangement for coppering, 144 Hydrochloric acid, 220, 481 dip, 288 Hydrocyanic acid, 160,481 poisoning by, 510 Hydrofluoric acid, 120 Hydrogen, 4, 71, 513 evolution of, during depo- sition, 393 sulphuretted, 292, 361 Hypochlorite of lime, 439 Hyposulphite of silver, 227 TMITATION antique silver, 269 Immersing the work in the bath, 304 Immersion, simple, deposition of pla- tinum by, 350 deposition of silver by, 230 deposition of tin by, 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. 545 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 anodes, 341, 397 articles, tinning, by simple im- mersion, 331 battery, Callan's, 1 1 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 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 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-deposition of, 340 zinc, Ac., plating, 250 Isonandra gutta, 94 TACOBI'S discovery, announcement J 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, 1 60 cheap, gilding, 213 ,, coloured, 199 French, gilding, 212 Jointing belts, 488 Jordan's discovery, Dircks on, 59 process, 53 TZAPP and Allen's dynamo-electric machine, 37 Keeper, 22 Keeping up the strength of 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 ABELS, zinc, printing on, 346 Lac carmine, 385 54^ INDEX. Lacquering electro-brassed work, 387 Lambert's process for treating gold and silver ores, 437 Lamps, table, &c., nickeling, 308 Lanthanum, 513 Lathe, foot, for polishing, 456 ,, scratch-brush, 179, 247 polishing, 249, 452 Lead, 357, 513 ,, acetate of, 357 anode, 358 black, 385 ,, Britannia metal, &c., gilding, 216 ,, chromate of, 385 ,, crystalline, 434 ,, deposition of, 357 ,, mounts, treatment of, 254 ,, nitrate of , 357, 428 ,, oxide of, 96, 357 ,, peroxide of, 358 pewter and tin work, electro- brassing, 381 ,, refining, Keith's process, 428 ,, salts of, 428 ,, and sodium, chloride of, 357 ,, solution, 358 sugar of, 357, 475 ,, sulphate of , 428 Leading rods, 188, 308 wires, 188 Leather belt, 458 belts, 487 ,, bull-neck, 452, 456 ,, chamois, 271 ,, hippopotamus, 452 ,. walrus, 452 Leclanch6's battery, 15 Lenoir's coppering process. 140 L6trange's zinc process, 439 Ley, caustic, 390 Lime, acetate of, 296 ,, carbonate of , 454, 485 ,, caustic, 231 ,, chloride of, 392 bob, 455 ,, finishing, 454 Lime, hypochlorite of, 439 ,, milk of, 236 ,, Sheffield, 315,454 ,, slaked, 303 ,, used in finishing nickel-plated work, 323 Liqueur stands, &c., plating, 245, 252 Liquid ammonia, 296, 481 ,, brightening, 276 ,, soldering, 507 Litharge, 96, 357 Lithium, 513 Liver of sulphur, 140 Lockets, gilding, 177, 179 London wet-colouring process Long work, nickeling, 312 Lubrication, 493 Luckow's zinc process Lustre, bright, dip for, 236 ,, dead, dip for, 237 ,, bright dead, 188 MACHINE, dynamo-electric, Car- lyle's.35 Machine, dynamo-electric, Chutter's, 488 ,, dynamo-electric, (jiilchei's, 37 , , dynamo-electric , Hallett-El- more, 33 dynamo-electric, Kapp and * Allen's, 37 dynamo-electric, Mather's, 37 ,, dynamo-electric, Schukert's, "36 dynamo-electric, Siemens', 30 ,, dynamo-electric, Weston's, 32 ,, hand-shaving, 135 magneto-electriCjG ramineV, 27 ,, magneto-electric, Saxton's, 23 ,, magneto-electric, Wilde's, 25 INDEX. 547 Machine, magneto-electric, Wool- rich's, 25 ,, planing and shaving, 136 ,, plumbagoing, 129 Machines.dynamo, advantages of gas- engines in driving, 491 dynamo-electric, 249 dynamo-electric, manage- ment of, 491 dynamo, nickeling by, 306 ,, over-heating of, 493 Madder, 207 Magnesia, 227 ,, ammonio-sulphate of, 390 ,, sulphate of, 343, 390 Magnesium, 513 ,, and its alloys, deposition of, 390 and ammonium, double chloride of, 365 bronze, 391 chloride of, 365 ,, deposition of, 365 Magnet, artificial, 21 ,, compound, 24 Magnetised needle, 18 Magnetism, electro, 18 ,, induced, 21 ,, residuary, 30 Magneto-electric machine, Gramme's, 27 ,, machine, Saxton's,23 ,, machine, Wilde's, 25 ,, ,, Woolrich's, 25 machines, 249, 399 ,, machines, nickeling with, 306 Magneto-electricity, 21 Magnets, 401 ,, electro, 21 ,, horse-shoe, 21 Main driving belts, 487 Making copper moulds by electro- lysis, 153 Making electrotype plates from drawings, 153 Malachite, 435 Malleability of metals, 498 Malleable brass, 503 Management of batteries, 494 ,, dynamo-electric ma chines, 491 gold baths, 21 1 Manganese, 365, 513 ,, deposition of, 365 ,, peroxide of, 15 Manganium, deposition of, 365 Marchese's process for electrolytic ex- traction of copper from ores, 437 Marie-Davy battery, 16 Marine glue and gutta-percha com- position for moulds, 95 Martial pyrites, 442 Materials used in electro-deposition, 475 Mather's dynamo-electric machine, 37 Matt, copper, 437 Matted, or dead gold, 185 Maynooth battery, 1 1 Measures and weights, table of, 517 Mechanical force, 29 Medallions, copying plaster of Paris, 103 Medals, &c., copying, 99 Mercurial bronze, 514 poisoning, 185 solution, 189, 203 Mercury, 233, 263, 513 ,, binoxide of, 231 ,, bisulphide of, 16 chloride of, 362 cyanide of, 180 ,, dip, 1 80, 234 ,, ,, cyanide of, 234 ,, nitrate of, 234 ,, gilding, 202 gilding bright and dead in parts, 205 ,, gilding bronzes, 206 ,, gilding, colouring, 204 gilding, colouring paste for, 204 gilding, dead ormoulu, 208 548 INDEX. Mercury gilding, evaporation of the mercury, 204 ,, gilding French clocks, 207 ., gilding ormoulu colour, 206 gilding, preparation of the amalgam for, 202 gilding red gold colour, 206 ., re-gilding, 202 ,, a red ormoulu, 207 , , , , yellow ormoulu , 207 nitrate of, 180 ,, pernitrate of, 234 ,, red oxide of, 234 Metal, bell, 503 black, 404 blue, 404 Britannia, 258 ,, &c., electro-plating, 250 gilding, 167 ,, lead, &c., gilding, 216 chains, gilding, 180 fusible, 96, 503 ,, moulds from, 108 gilding, 1 80 ,, polishing, 451 pot, 503 prince's, 503 quantity of, deposited, 265 queen's, 503 shot, 503 speculum, 503 ,, tanks, 277 type, 503 white, 258 Metallic bronze powders, 484 ,, contact, 117 ,, discs, 2 ,, electrodes, 55 ,, salts, poisoning by, 511 Metallising the moulds, 130 the moulds, Adams' pro- cess for, 131 Metallo-chromes, 358 on nickel-plated sur- faces, 360 Metallo-chromy, 358 Metallurgy, electro, 395 ,, ,, of copper, 401 ,, ,, of lead, 428 ,, of zinc, 439 Metals, characteristics of, 498 conductivity of, 87 different, brassing, 393 ,, ductility of, 499 ,, gilding different, 209 ,, malleability of, 498 ,, plating different, at the same time, 275 relative conducting power of, 82 ,, relative conductivity of, 514 stripping, from each other, 466 ,, tenacity of , 499 thermo-electric order of, 41 tinning, Dr. Hillier's method of, 334 ,, various, electro-deposition of r 348 Method, dry, extraction of silver by, 464 ,, French, of bronzing electro- brassed zinc work, 386 ,, Heeren's, of tinning iron wire, 334 Hillier's, Dr., of tinning me- tals, 334 simple, of preparing nickel salts, 298 wet, extraction of silver by, 463 Methylated spirit, 384 Milk of lime, 236 Milled zinc, 345 Minerals, aluminous, 449 Molybdenum, 501, 513 I Monosilicate of potash, 365 Mop, finishing, 457 Morris & Johnson's German silver process, 389 Johnson's process for brass- ing, 372 INDEX. 549 Mosaic gold, 503 I Motion given to articles in the bath, j 243 Mould, clearing the, 105 connecting the wire to the, 109 electrotype, 264 ., press for, 127 plumbagoing the, 128 preparing the, 104, 125 Moulding case, 126 composition, 125 in gutta-percha, 99 ., in plaster of Paris, 115 material, elastic, 97 materials, 94 or taking the impression 126 Mouldings, 184 Moulds, Adams' process of metallis- ing, 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, 327 gauze wire, 321 long pieces of work, 312 mullers, &c., 309 plant, arrangement of, 306 potash bath for, 286 Powell's process, 296 preparation of work for, 285, 301 printing rollers, 321 purse frames, *fec., 306 small articles, 326 small brass and cop- per articles, 306 Unwin's process, 294 , , Weston's process, 295 workshop, 30 Nickeling bath for facing electro- types, 320 ,, bicycles, 313 ., bicycle spokes, 313 ,, bits, spurs, &c., 308, 316 ,, book clasps, &c., 322 ,, brass and copper work 302 ,, brass taps, 305 ,, 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 ,, dentists' tools, &c., 305 by dynamo-electricity, 30& forceps, &c., 323 ,, handrails, &c., 312 harness furniture, 316 ,, kilting machines, 327 ,, notes, 322 plant, arrangement of , 3O& printing rollers, 32 1 railway keys, &c., 326 re-, old work, 319 ,, reticule frames, &c. 306 ,, sanitary work, &c., 311 ,, sausage warmers, &c., 309 screws, &c., 305 ., second-hand bicycles, 314 ships' deck lamps, 312, 327 shop fronts, 312 small articles by dynamo - electricity, 326 ,, small brass and copper articles, 306 ,, small screws, 326 small steel articles, 305 steel articles, 305, 322 stove fronts, &c., 313 stirrups, 317 ., solution for tin, Britan- nia metal, &c., 298 solutions, preparation of, 291 ,, sword scabbards, 315 INDEX. 55 1 Nickeling table lamps, &c., 308 umbrella mounts, &c., 306 wire gauge, 321 Nielled silver, 273 Nielling composition. 273 Niello, 273 Niobium, 513 Nitrate of binoxide of mercury, 189 bismuth, 355 lead, 357, 428 mercury, 180 dip, 234 potash, 252 silver, 219, 390 ,, preparation of, 219 ,, soda, 252, 430 ,, zinc, 443 Nitric acid, 264, 356, 483 battery, 10 ,, dip, 236 ,, fuming, 236, 481 Nitre, 198, 236 Nitro-hydrochloric acid, 476 Nitro-sulphuric acid, 180 Nitrous acid, 236 Nobili's rings, 359 Noe's thermo-electric battery, 49 Nomenclature of electro-chemical ac- tion, Faraday's, 70 Non-conducting substances, coating with copper, 156 Non-conductors, 78 Non-metallic substances, to render conductive, 119 Notes, coppering, 154 ,, on electro-brassing, 392 ,, on gilding, 208 ,, nickeling, 274 ,, silvering, 274 Nuremberg powder, 189 rvBSERYATlONS on commercial ^ cyanide of potassium, 221 Observations on electro-brassing, 382 on gilding in cold baths, 174 Dr. Higgs', on the depo- sition of copper, 406 Observations, Professor Keith's, on re- fining copper by elec- trolysis, 401 ,, Kiliani's, on the electro- lytic refining of cop- per, 406 ,, Dr. Siemens' on the electro-metallurgy of copper, 401 ,, on preparing work for nickel-plating, 285 Ochre, red, 271 Oersted's discovery, 18 Ohm's law, 85 application of, to com- pound voltaic circles, 86 Oil of vitriol, 180, 237, 486 Old cyanide solutions, recovery of gold and silver from, 461 gold solutions, 209, 210 plated articles, stripping silver from, 252 candlesticks, 256 sugar bowls, &c., 255 ,, ware, preparation of, for resilvering, 251 slinging wires, 278 solutions, recovery of nickel from, 324 work, buffing, after stripping, 253 work, re-nickeling, 319 replating, 251 ; Ore, cobalt, 352 Ores, Becquerel's process for treating, 434 ,, carbonate of copper, 396 electrolytic treatment of, 434 extraction of copper from, by electrolysis, Marchese's pro- cess, 437 gold, 434 gold, electro-chlorination of, Cassel's process, 438 gold and silver, Lambert's pi o- cess of treating, 437 ,, sulphuretted, 442 INDEX. Ores, zinc, 439 Origin of the porous cell, 63 Ormoulu, 207, 503 colour, 206 colouring mixture, 206 dead, 208 red, 207 ,, yellow, 207 Ornamental bronzes, gilding, 163 gilding, 197 Osmium, 513 Overheating of dynamos, 493 Oxalate of ammonia, 292 Ox gullet, 9 Oxidation, 180, 267 Oxide of aluminium, hydrated, 444 boric, 449 of copper, 267, 396 cupreous, 409 of iron, 327, 380 of lead, 96, 357, 359 ,, of mercury, red, 234 ,, of nickel, 298 ,, of silver, 224, 227 of tin, 372 ,, of zinc, 346, 396, 447 Oxidised silver, 269, 472 Oxidising, 269 chandeliers, 271 copper surfaces, 500 ,, Dr. Eisner's process, 271 ,, and part-gilding, 271 ,, with the paste, 270 ,, satin finish, 271 silver, 269 ,, small articles, 271 with solution of platinum, 270 ,, statuettes, 271 ,, with sulphide of ammo- nium, 271 ,, with sulphide of potas- sium, 270 ,, or sulphuring silver, 272 ,, vases, 271 ,, Wahl's process for, 271 Oxychloride of antimony, 356 Oxygen, nascent, 441 "DALE straw-coloured gold, 198 Palladium, 501, 513 Palladium anode, 354 electro-deposition of, 354 solution of ammonio- chloride of, 354 solution of chloride of, and ammonium, 354 Paraffin wax, 93 Parkes' plating solution, 224 Part-gilding and oxidising, 271 Paste, bronzing, 385 for green bronze, 385 oxidising with the, 270 Patens, gilding, 187 Pearlash, 231, 463, 4?6 Pepys' water battery, 15 Perchloride of iron, 255, 264 solution of, 507 Pernitrate of mercury, 234 of mercury, solution of, 2*, Peroxide of iron, 206, lead, 358 manganese, 15 tin > 332 Person and Sire's brassing process, 378 zincing solution, 346 Pewter, 503 lead and tin work, electro- brassing, 381 solder, 259 solder, electro-silvering, 277 solder, gilding, 212 tin, &c., plating, 250 Phosphate of soda, 194 nickel, 296 Phosphide of copper, 51 tin, 514 Phosphor bronze, 514 Phosphoric solution, 342 Phosphorus, 119, 228, 342, 484 solution of, 485 Pickle, sulphuric acid, 193, 290 for zinc work, 380 Pickles, 290, 484 INDEX. 553 Pickling bath for cast iron, 290 Pile, voltaic, 5 Pimple copper, 401 Pinaire's method of gilding watch movements, 188 Pink gold, 198 tint upon silver, 274 Pins, brass, electro-tinning, 331 Plant, nickeling, arrangement of, 306 Plant's secondary battery, 17 Plaster busts, copying, 112 medallions, wax moulds from, 106 moulds, electrotyping from, 136 of Paris, 98 of Paris medallions, copying, 103 of Paris, moulding in, 1 15 Plastic gutta-percha, 95 Plate, electro, characteristics of, 259 resilvering, 258 ship, replating, 251 Plated articles, stripping gold from insides of, 256 candlesticks, old, 256 electro articles, whitening, 267 nickel articles, stripping, 469 or silver work, polishing, 455 ware, old, preparation of, for resilvering, 251 Plates, zinc, 242 amalgamating, 92 Platiu, 504 Plating balance, 261 bath, arrangement of, 241 ,, bath, brightening solution for, 229 ., bath, preparation of new work for, 233 battery, 242 brass, &c., 250 ,, bright, 228, 277 Britannia metal, &c., 250 cruet stands, for a stout coating, 215 Hilliefs, Dr., for tinning metals, 334 ,, mercurial, 189, 203 ,, nickel, preparation of, 283 ,, for nickeling tin, &c., 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 Koseleur'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 antimony, 355, 356 ,, brassing, 367, 368 ,, bronzing, 371 ,, cobalt, 353 ,, copper, specific resistance of, 5i5 copper, working of, 155 coppering, 147 ,, alkaline, 147 ,, cyanide, 462 INDEX. 563 Solutions, old cyanide, recovery of silver from, 462 gilding, 215 j, ,, preparation of, 167 ,, treatment of, 208 old gold, 210 gold, strengthening, 173 , , hot brassing, 394 ,, nickel, common salt in, 325 } , . nickeling, preparation of, j 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 oi 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, 1 86 ,, iron, zinc, &c., stripping silver from, 468 ,, polishing, 455 ,, shot, coppering, 154 ,, wire, coppering, for telegraph purposes, 146 Steele's process of gilding by contact with zinc, 164 tinning process, 337 Steeps, or dips, 287 Stereotype metal, 133 ,, plates, brassing, 382 Stirrups, nickeling, 317 Stopping, 130 ,, off, 470 off composition, 471 ,, off varnishes, 471 , , off varnishes, applying, 47 1 Stove and fender work, brassing, 392 ,, fronts, bronzing, 384 ,, ,, &c., nickeling, 313 Strength of commercial cyanide, to determine, 479 ,, tensile, of electrolytic cop- per, 145 Strengthening gold solutions, 173 Strontium, 513 Stripping, 213 ,, acid for nickel-plated ar- ticles, 470 ,, bath for silver, 252, 462 ,, ,, nickel, 319, 470 5 6 4 INDEX. Stripping gold from insides of plated articles, 256 ,, gold from silver, 213, 469 ,, metals from each other, 466, 467 ,, nickel-plated articles, 469 ! ,, silver by battery, 468 ,, silver from iron, steel, zinc, ! &c., 468 ,, silver from old plated ar- ticles, 252 ,, solution, cold, 253 , , solution, cold,f or silver,468 ,, solutions, 466 ,, solutions, old, recovery of gold and silver from, 465 ,, spoons and forks, 467 Sublimate, corrosive, 231 Subnitrate of bismuth, 355 Sugar basins, gilding, 183 bowls, mugs, &c., old plated, 255 of lead, 357, 475 Sulphate of alumina, 332, 362 ammonia, 295, 332, 334 cadmium, 364 copper, 91, 397, 485 ,, copper baths, Gramme's experiments with, 411 copper, electrolysis of, 75 iron, 93, 344. 396 ,, iron and chloride of ain- nionium solution, 344 lead, 428 -magnesia, 343, 390 ,, nickel, 295 peroxide of iron, 435 ,, potash, &c., electrolysis of, 76 ,, silver, 225 ,, soda, 225 zinc, 199, 396 Sulphide of ammonium, 101 ,, ammonium, oxidising with, 271 barium, 500 ,, calcium, 292 iron, 136, 435 Sulphide of potassium, 140, 292 ,, potassium, oxidising with, 270 ,, silver, 227 ,, sodium, 292, 300 zinc, 439, 443 Sulphides, cupric, 441 ,, natural, electrolytic treat- ment of, 441 Sulphur, 272, 513 ,, fused, 273 ,, liver of, 140, 270 Sulphuret of antimony, 355 Sulphuretted hydrogen, 292, 361 ores, 442 Sulphuric acid, 234, 242, 486 ,, pickle. 193 ,, ether, 187, 342 Sulphuring silver, 272 Sulphurous acid gas, 397 Suspending rods, 274, 308 ,, cleaning, 276 ,, umbrella mounts, 327 Swansdown, 457 Sword mounts, gilding, 185 ,, scabbards, nickeling, 315 Symbols and atomic weights of ele ments, 513 TABLE lamps, fec., nickeling, 308 Table of weights and measures, 517 Tables, useful, 513 Tallow and crocus composition, 327 Tank, depositing, 281 ,, depositing, for tin, 335 ,, hot water, 286 ,, potash, 286 Tankards, mugs, &c., gilding, 210 Tanks, depositing, 241 iron, 277 ,, nickel-plating, 306, 308 ,, plating, gutta-percha lined, 279 ,, slate, 241 ,, wrought-iron, 241 Tantalum, 513 Taps, brass, nickeling, Tartar, cream of, 189, 331 INDEX. S65 Tartar, salt of, 224 Tartaric acid, 334 Tartrate of zinc, 346 Tea and coffee services, plating, 246, 254 Tellurium, 513 Temperatures, high, table of, 515 Tenacity of metals, 499 Tensile strength of electrolytic cop- per, 145 Tension, 28, 83 Terchloride of antimony, 355 of gold, 157, 439 Teroxide of antimony, 356, 430 Tersulphuret of antimony, 356 Test for free cyanide, 499 Thallium, 513 Theory of electrolysis, 70 Thermo-electric battery, Xoe's, 49 battery, C. Watt's, 42 current, 41 laws, 41 order of metals, 41 pairs, 41 pile, 41 ,, ., pile, diamond's, 45 piles and batteries,42 ,, series, 40 Thermo-electricity, 39 ,, ,, Seebeck's dis- covery of , 39 the future of r 49 Thermo-pile, Becquerel's, 45 Wray's, 48 Thermometer, &c., scales, silvering, 231, 232 scales, French and English, compara- tive, 516 Thick brass deposits, 378 Thickness of electro-deposited silver, 265 ,, of electrotype, 156 Thomas and Tilley's process, for de- position of aluminium, 362 Thorium, 513 Time-pieces, gilding, 187 Tin, 501, 513 ,, and alum, solution of, 332 ,, anode, 390 ,, anodes, 335 ,, Britannia metal, &c., nickeling solution for, 298 ,, bronze powder, 131 chloride of, 331, 332 ,, concentrated solution of, 336 ,, deposition of, 331 ,, deposition of, by simple immer- sion, 331 ,, deposition of, by single cell process, 334 electro-deposition of, 331, 335 ,, grain, 331, 332 ,, oxide of, 372 ,, peroxide of , 332 ,, pewter and lead work, electro - brassing, 381 ,, phosphide of, 514 ,, powder for electrotyping, 138 ,, protochloride of, 331 ,, recovery of, from tin scrap, by electrolysis, 338 ,, salt, 390 ,, sheet, anodes, 336 ,, and silver alloy, deposition of, 389 ,, and silver, solution of, 389 Tinned, electro, articles, re-plating. 260 Tinning and backing the electrotype, 133 ,, by contact with zinc, 332 ,, depositing tank for, 335 ,, electro, brass pins, 331 ,, Fearn's process for, 336 ,, iron articles by simple im- mersion, solution for, 331 ,, iron wire, Heeren's method of, 334 ,, liquid, 133 metals, Dr. Hillier's method of, 334 salt, 477, 506 ,, simple solution for, 332 solutions for, 332 5 63 Worn anodes, INDEX. Wray's thermo-pile, 48 Wrought-iron tanks, 241 ,, work, electro-brassing, 380 preparing, for zincing, 346 "yELLOW ormoulu, 207 Yellow prussiate of potash, 227, 344, 477, 481 Yttrium, 513 7INC, 501, 513 Zinc, acetate of, 346, 372 Zinc, amalgamating, 4, 92 ,, anode, 345 articles, electro-gilding, 192 ,, bath for tinning, 332 ,, Bias and Heist's process for treating sulphide of, 442 ,, blende, 443 ,, carbonate of, 439 ,, castings, preparation of, for gilding, 192 ,, chloride of, 443, 477, 507 ,, and coke anode, 441 ,, cyanide of , 372 ,, electrolytic, as a printing sur- face, 346 , , electro-metallurgy of, 439 ,, filings, 461 , , gilding by contact with, Steele's process, 164 ,, to granulate, 333 Zinc, granulated, 333 ,, Hermann's, process, 347 ,, and iron, electro-deposition of, 340 iron, &c., plating, 250 ,, iron and steel, stripping silver from, 468 , , Letrange's process for treating ores of, 439 ,, Luckow's process for extrac- tion of, 441 ,, metallic, 439 ( j ,, milled, 345 ,, nitrate of, 443 ,, oxide of, 346, 396, 447 ,, ores, 439 ,, plates, 242 ,, process, Werderniann's, 443 ,, sulphate of, 199, 396 ,, sulphide of, 439, 443 ,, tinning, by contact with, 332 , , tinning, by simple immersion , 332 ,, Watt's solution for deposition of, 345 ,, work, electro-brassed, French method of bronzing, 386 ,, work, electro-brassing, 380 ,, work, pickle for, 380 Zincing, preparing cast-iron work for, 346 ,, preparing wrought - iron work for, 346 ,, solutions, 346 Zirconium, 513 PRINTED BY J. 8. 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On a Sheet, zs.6d. 6 CROSBY LOCK WOOD &> CO. 'S CATALOGUE. Tables for Setting-out Curves. TABLES OF TANGENTIAL ANGLES AND MULTIPLES for Setting-out Curves from 5 to 200 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." Athentzum. Engineering FieldworJc. THE PRACTICE OF ENGINEERING FIELDWORK, applied to Land and Hydraulic, Hydrographic, and Submarine Surveying and Levelling. Second Edition, Revised, with considerable Additions, and a Supplement on Waterworks, Sewers, Sewage, and Irrigation. By W. DAVIS KASKOLL, C.E. Numerous Folding Plates. In One Volume, demy 8vo, i 55. cloth. Large Tunnel Shafts. THE CONSTRUCTION OF LARGE TUNNEL SHAFTS : A Practical and Theoretical Essay. By J. H. WATSON BUCK, M. Inst. C.E., Resident Engineer, London and North-Western Railway. Illustrated with Folding Plates, royal 8vo, 125. cloth. "Many of the methods given are of extreme practical value to the mason ; and the observations on the form of arch, the rules for ordering the stone, and the construction of the templates will be found of considerable use. We commend the book to the engineering profession." BiiUding News. "Will be regarded by civil engineers as of the utmost value, and calculated to save much time and obviate many mistakes." Colliery Guardian. Field-Boole for Engineers. THE ENGINEER'S, MINING SURVEYOR'S, AND CON- TRACTOR'S FIELD-BOOK. Consisting of a Series of Tables, with Rules, Explanations of Systems, and use of Theodolite for Traverse Surveying and Plotting the Work with minute accuracy by means of Straight Edge and Set Square only ; Levelling with the Theodolite, Casting-out and Reducing Levels to Datum, and Plotting Sections in the ordinary manner; setting-out Curves with the Theodolite by Tangential Angles and Multiples, with Right and Left-hand Readings of the Instrument: Setting-out Curves without Theodolite, on the System of Tangential Angles by sets of Tangents and Off- sets : and Earthwork Tables to 80 feet deep, calculated for every 6 inches in depth. By W. DAVIS HASKOLL, C.E. With numerous Woodcuts. Fourth Edition, Enlarged. Crown 8vo, I2S. cloth. "The book is very handy, and the author might have added that the separate tables of sines and tangents to every minute will make it useful for many other purposes, the genuine traverse tables existing all the s&me."j4the!uziim. "Every person engaged in engineering field operations will estimate the importance of such a work and the amount of valuable time which will be saved by reference to a set of reliable tables prepared with the accuracy and fulness of those given in this volume." Railway News. Earthwork, Measurement and Calculation of. A MANUAL ON EARTHWORK. By ALEX. J. S. GRAHAM, C.E. With numerous Diagrams. i8mo, zs. 6d. cloth. "A great amount of practical information, very admirably arranged, and available for rough estimates, as well as for the more exact calculations required in the engineer's and contractor's offices." Artizan. Strains. THE STRAINS ON STRUCTURES OF IRONWORK; with Practical Remarks on Iron Construct : on. By F. W. SHEILDS, M. Inst. C.E, Second Edition, with 5 Plates. Royal 8vo, 55. cloth. "The student cannot find a better little book on this subject." Engineer. Strength of Cast Iron, etc. A PRACTICAL ESSAY ON THE STRENGTH OF CAST IRON AND OTHER METALS. By THOMAS TREDGOLD, C.E. Fifth Edition, including HODGKINSON'S Experimental Researches. 8vo, las. cloth. MECHANICS & MECHANICAL ENGINEERING. 7 MECHANICS & MECHANICAL ENGINEERING. The Modernised "Tetngleton." THE PRACTICAL MECHANICS WORKSHOP COM- PANION. Comprising a great variety of the most useful Rules and Formulae in Mechanical Science, with numerous Tables of Practical Data and Calcu- lated Results for Facilitating Mechanical Operations. By WILLIAM TEMPLE- TON, Author of "The Engineer's Practical Assistant," &c. &c. An Entirely New Edition, Revised, Modernised, and considerably Enlarged by WALTER S. HUTTON, C.E., Author of "The Works' Manager's Handbook of Modern Rules, Tables, and Data for Engineers," &c. Fcap. 8vo, nearly 500 pp., with 8 Plates and upwards of 250 Illustrative Diagrams, 6s., strongly bound for workshop or pocket wear and tear. [Just published. &2r TEMPLETON'S " MECHANIC'S WORKSHOP COMPANION " has been for more than a quarter of a century deservedly popular, having run through numerous Edi- tions; and, as a recognised Text-Book and well-worn and thumb-marked vade mecum of several generations of intelligent and aspiring workmen, it has had the reputation of hiving been the means of raising many of them in their position in life. In its present greatly Enlarged, Improved and Modernised form, the Publishers are sure that it will commend itself to the English workmen of the present day all the world over, and become, like its predecessors, their indispensable friend and referee. A smaller type having been adopted, and the page increased in size, while the number of pages has advanced from about 330 to nearly 500, the book practically con- tains double the amount of matter that was comprised in the original work. \* OPINIONS OF THE PRESS. " In its modernised form Hutton's ' Templeton ' should have a wide sale, fo it contains much valuable information which the mechanic will of ten find of use, and not a few tables and notes which he might look for in vain in other works. This modernised edition will be appreciated by all who havelea rned to value the original editions of ' Templeton.' 'English Mechanic. 'U has met with great success in the engineering workshop, as we can testify ; and there are great many men who, in a great measure, owe their rise in life to this little book."uMc(iH& eu's. Engineer's and Machinist's Assistant. THE ENGINEER'S, MILLWRIGHT'S, and MACHINIST'S PRACTICAL ASSISTANT. A collection of Useful Tables, Rules and Data. By WILLIAM TEMPLETON. Seventh Edition, with Additions. i8mo, zs. 6d. cloth. " Templeton's handbook occupies a foremost place among books of this kind. A more suitable esent to an apprentice to any of the mechanical trades could not possibly be made." Building T.US. Turning. LATHE-WORK : A Practical Treatise on the Tools, Appliances, and Processes employed in the Art of Turning. By PAUL N. HASLUCK. Third Edition, Revised and Enlarged. Crown 8vo, 55. cloth. " Written by a man who knows, not only how work ought to be done, but who also knows how i Shipping Chronicle. MECHANICS & MECHANICAL ENGINEERING. 9 Steam Boilers. A TREATISE ON STEAM BOILERS: Their Strength, Con- struction, and Economical Working. By ROBERT WILSON, C.E. Fifth Edition. 121110, 6s. cloth. "The best treatise that has ever been published en steam boilers." Engineer. "The author shows himself perfect master of his subject, and we heartily recommend all em- ploying- steam power to possess themselves of the work," Rutland's Iron Trade Circular. Boiler Making. THE BOILER-MAKER'S READY RECKONER. With Ex- amples of Practical Geometry and Templating, lor the Use of Platers, Smiths and Riveters. By JOHN COURTNEY, Edited by D. K. CLARK, M.I.C.E. Second Edition, revised, with Additions, i2ino, 55. half-bound. " A most useful work No workman or apprentice should be without this book. Iron Trade Circular. " A reliable guide to the working boiler-maker." Iron. " Boiler-makers will readily recognise the value of this volume. . . . The tables are clearly printed, and so arranged that they tan be referred to with the greatest facility, so that it cannot be doubted that they will be generally appreciated and much used." Mining journal. Steam Engine. TEXT-BOOK ON THE STEAM ENGINE. By T. M. GOODEVE, M.A., Barrister-at-Law, Author of "The Elements of Mechanism," - &c. Seventh Edition. With numerous Illustrations. Crown 8vo, 6s. cloth. " 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. Steam. THE SAFE USE OF STEAM. Containing Rules for Un- professional Steam-users. By an ENGINEER. Fifth Edition. Sewed, 6d. " If steam-users would but learn this little book by heart, boiler explosions would become sensations by their rarity." English Mechanic. 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. "This is a very useful book, containing very useful tables. The results given are well chosen, and the volume contains evidence that the author really understands his subject. We can recom- mend the work with pleasure." Mechanical World. " These tables are designed to meet the requirements of every-day use ; they are of sufficient scope for most practical purposes, and may be commended to engineers and users of steam." 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 hey should comply, is accurate and full." Engineer. Gas Lighting. COMMON SENSE FOR GAS-USERS: A Catechism of Gas- Lighting for Householders, Gasfitters, Millowners, Architects, Engineers, etc. By ROBERT WILSON, C.E., Author of " A Treatise on Steam Boilers." Second Edition. Crown 8vo, sewed, with Folding Plates and Wood En- gravings, 2S. 6d. " All gas-users will decidedly benefit, both in .pocket and comfort, if they will avail themselves of Mr. Wilson's counsels." Engineering. io CROSBY LOCK WOOD & CO. 1 S CATALOGUE. THE POPULAR WORKS OF MICHAEL REYNOLDS (Known as " THE ENGINE DRIVER'S FRIEND "). Locomotive-Engine Driving. LOCOMOTIVE-ENGINE DRIVING : A Practical Manual for Engineers in charge of Locomotive Engines. By MICHAEL REYNOLDS, Member of the Society of Engineers, formerly Locomotive Inspector L. B. and S. C. R. Seventh Edition. Including a KEY TO THE LOCOMOTIVE ENGINE. With Illus- trations and Portrait of Author. Crown 8vo, 45. 6d. cloth. "Mr. Reynolds has supplied a want, and has supplied it well. We can confidently recommend the book, not only to the practical driver, but to everyone who takes an interest in the performance of locomotive engines." The Engineer. "Were the cautions and rules given in the book to become part of the evcry-day working of our engine-drivers, we might have fewer distressing accidents to deplore." Scotsman. The Engineer, Fireman, and Engine-Boy. THE MODEL LOCOMOTIVE ENGINEER, FIREMAN, and ENGINE-BOY. Comprising a Historical Notice of the Pioneer Locomotive Engines and their Inventors, with a project for the establishment of Certifi- cates of Qualification in the Running Service of Railways. By MICHAEL REYNOLDS, Author of "Locomotive-Engine Driving." With numerous Illus- trations and a fine Portrait of George Stephenson. Crown 8vo, 45. 6d. cloth. " From the technical knowledge of the author it will appeal to the railway man of to-day more forcibly than anything written by Dr. Smiles. . . . The volume contains information of a tech- nical kind, and facts that every driver should be familiar with." English Mechanic. "We should be glad to see this book in the possession of everyone in the kingdom who has ever laid, or is to lay, hands on a locomotive engine." Iron. Stationary Engine Driving. STATIONARY ENGINE DRIVING : A Practical Manual for Engineers in charge of Stationary Engines. By MICHAEL REYNOLDS. Third Edition, Enlarged. With Plates and Woodcuts. Crown 8vo, 45. 6d. cloth. "The author is thoroughly acquainted with his subjects, and his advice on the various points treated is clear and practical. . . . He has produced a manual which is an exceedingly useful one for the class for whom it is specially intended." Engineering. "Our author leaves no stone unturned. He is determined that his readers shall not only know something about the stationary engine, but all about it." Engineer. Continuous Railway Brakes. CONTINUOUS RAILWAY BRAKES : A Practical Treatise on the several Systems in Use in the United Kingdom ; their Construction and Performance. With copious Illustrations and numerous Tables. By MICHAEL REYNOLDS. Large crown 8vo, gs. cloth. " A popular explanation of the different brakes. It will be of great assistance in forming public opinion, and will be studied with benefit by those who take an interest in the brake." ritis/t Mechanic. "Written with sufficient technical detail to enable the principle and relative connection of the various parts of each particular brake to be readily grasped." Mechanical IVorld. Engine-Driving Life. ENGINE-DRIVING LIFE; or, Stirring Adventures and Inci- dents in the Lives of Locomotive-Engine Drivers. By MICHAEL REYNOLDS. Ninth Thousand. Crown 8vo, 2S. cloth. "The book from first to last is perfectly fascinating. Wilkie Collins' most thrilling conceptions are thrown into the shade by true incidents, endless in their variety, related in every page." North British Mail. "Anyone who wishes to get a real insight into railway life cannot do better than read ' Engine- Driving Life' for himself ; and if he once take it up he will find that the author's enthusiasm and real love of the engine-driving profession will carry him on till he has read every page." Saturday Revie-w. PocJcet Companion for Enginemen. THE ENGINEMAN'S POCKET COMPANION AND PRAC- TICAL EDUCATOR FOR ENGINEMEN, BOILER ATTENDANTS, AND MECHANICS. By MICHAEL REYNOLDS, Mem. S. E., Author of "Locomotive Engine- Driving," "Stationary Engine-Driving," &c. With Forty-five Illustrations and numerous Diagrams. Royal i8mo, 35. 6d., strongly bound in cloth for pocket wear. U"st published. ARCHITECTURE, BUILDING, etc. n ARCHITECTURE, BUILDING, etc. Construction. THE SCIENCE OF BUILDING : An Elementary Treatise on the Principles of Construction. By E. WVNDHAM TARN, M.A., Architect. Second Edition, Revised, with 58 Engravings. Crown 8vo, js. 6d. cloth. " 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 ArcJiitecture. 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. 30 Plates, 410, half-morocco, gilt edges, i is. *** Also an Enlarged Edition of the above. 61 Plates, with Outline Speci- fications, Estimates, &c. 2 2s. half-morocco. " 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. Useful Text-BooJc for Architects. THE ARCHITECT'S GUIDE: Being a Text-Book of Useful Information for Architects, Engineers, Surveyors, Contractors, Clerks of 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 Home. 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 Hates, half-bound, 3 35. N.B. This is the only book which gives on a large scale, and with the pre- cision of 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 examples 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. Draiving for Builders and Students in Architecture. PRACTICAL RULES ON DRAWING, for the Operative Builder and Young Student in Architecture. By GEORGE PYNE. With 14 Plates, 4to, 75. 6d. boards. Civil Architecture. THE DECORATIVE PART OF CIVIL ARCHITECTURE. By Sir WILLIAM CHAMBERS, F.R.S. With Illustrations, Notes, and an Examination of Grecian Architecture, by JOSEPH GWILT, F.S.A. Edited by W. H. LEEDS. 66 Plates, 4to, 2is. cloth. TJie House-Owner's Estimator. 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 the late JAMES D. SIMON, A.R.I.B.A. Edited and Revised by FRANCIS T. W. MILLER, A.R.I.B.A. With numerous Illustrations. Third Edition, Revised. Crown 8vo, 35. 6d. cloth. 41 In two years it will repay its cost a hundred times over." Field. " A yery handy book." English Mechanic. 12 CROSBY LOCK WOOD & CO. '5 CATALOGUE. 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, and copious Memoranda lor the Valuation of Labour and Materials in the respective Trades of Bricklayer and Slater, Carpenter and Joiner, Painter and Glazier, Paperhanger, &c. With 8 Plates and 63 Woodcuts. Originally edited by EDWARD DOBSON, Architect. Fifth Edition, Revised, with considerable Additions on Mensuration and Construc- tion, and a New Chapter on Dilapidations, Repairs, and Contracts, by E. WYNDHAM TARN, M.A. Crown 8vo, 95. clotb. " 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. "The work has been carefully revised and edited by Mr. E. Wyndham Tarn, M.A., and com- prises several valuable additions on construction, mensuration, dilapidations and repairs, and other matters. . . . This edition will be found the most complete treatise on the principles of measur- ing and valuing artificers' work that has yet been published." Building Neius. Pocket Estimator. THE POCKET ESTIMATOR for the BUILDING TRADES. Being an Easy Method of Estimating the various parts of a Building collec- tively, more especially applied to Carpenters' and Joiners' work. By A. C. BEATON, Author of "Quantities and Measurements." Third Edition, care- fully revised, 33 Woodcuts, leather, waistcoat-pocket size, is. 6d. "Contains a good deal of information not easily to be obtained from the ordinary price books. The prices ^iven are accurate, and up to date." Building News. Builder's and Surveyor's Pocket Technical Guide. THE POCKET TECHNICAL GUIDE AND MEASURER FOR BUILDERS AND SURVEYORS. Containing a Complete Explana- tion of the Terms used in Building Construction, Memoranda for Reference, Technical Directions for Measuring Work in all the Building Trades, with a Treatise on the Measurement of Timber, Complete Specifications, &c. &c. By A. C. BEATON. Second Edition, with 19 Woodcuts, leather, waistcoat- pocket size, is. 6d. "An exceedingly handy pocket companion, thoroughly reliable." Builder 's Weekly Reporter. " This neat little compendium contains all that is requisite in carrying out contracts for ex- cavating, tiling, bricklaying, paving, &c." British Trade jfournal. 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 us. 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 the 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 Moyers' 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 Illusts., medium 8vo, 15$. cloth. \_Just published. " 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 through any defect in them " Architect. " Good forms for specifications are of cousiderable value, and it was an excellent idea to com- pile a work on the subject upon the basis of the late Alfred Bartholomew's valuable work. The second edition of Mr. Rogers's book is evidence of the want of a book dealing with modern re- quirements and materials." Building Neivs. DECORATIVE ARTS, etc. 13 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. Second and Cheaper Edition. Royal folio, i8fc by 12^ ia., Illustrated with 24 full-size Co- loured Plates ; also 12 plain Plates, comprising 154 Figures, price {i us. 6d. List of Contents Introductory Chapter Tools required for Methods of Working- Yellow Sienna Marble : Wood Painting Observations on the different Process of Working Juniper: Characteristics species of Wood: Walnut Observations on j of the Natural Wood: Method of Imitation Marble in general Tools required for Marble ! Vert de Mer Marble : Description of the Mar- Painting St. Remi Marble : Preparation of the ble: Process of Working Oak: Description of Paints : Process of Working Wood Graining '. the varieties of Oak : Manipulation of Oak- Preparation of Stiff and Flat Brushes: Sketch- painting: Tools employed: Method of Work- ing different Grains and Knots: Glazing of ing Waulsort Marble : Varieties of the Marble : Wood Ash: Painting of Ash Breche (Brec- Process of Working The Painting of Iron with cia) Marble : Breche Violette : Process of Work- j Red Lead: How to make Putty: Out-door ing Maple : Process of Working The different : Work : Varnishing : Priming and Varnishing speciesof White Marble: Methods of Working: : Woods and Marbles : Painting in General: Ceil- Painting White Mar ble with Lac-dye : Paini ing ! ings and Walls : Gilding : Transparencies, Flags, White Marble with Poppy-paint Mahogany : j &c. List of Plates. i. Various Tools required for Wood Painting 2, 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, *c. 8. 9. Ash: Pre- liminary Stages and Finished Specimen 10. Methods of Sketching Marble Grains u, 12. 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- ferent Species of White Marble 17, 18. White Finished Specimen 19. Mahogany : Specimens of various Grains and Methods of Manipulation 20, 21. 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, 36. Waulsort Marble: Varieties of Grain, Un- finished and Finished Specimens. Marble: Preliminary Stages of Process and "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 mea the opportunity to study \t" Builder. " 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 the student who aims at making his work a faithful transcript of nature." Building Ne-ws. Colour. A GRAMMAR OF COLOURING. Applied to Decorative Painting and the Arts. By GEORGE FIELD. New Edition, adapted to the use of the Ornamental Painter and Designer. By ELLIS A. DAVIDSON. With New Coloured Diagrams and Engravings. i2mo, 33. 6d. cloth boards. "The book is a most useful resume of the properties of pigments." Builder. 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. With 68 Cuts. 2s. cloth limp. "As a technical guide-book to the decorative painter it will be found reliable." Building News , %* By the same Author, just published. 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. With numerous Illustrations. i2mo, 25. 6d. cl. limp N.B. The above Two Works together in One Vol., strongly half-bound^ 55. Souse fainting, etc. HOUSE PAINTING, GRAINING, MARBLING, AND SIGN WRITING, A Practical Manual of. By ELLIS A. DAVIDSON. Fourth Edition. With Coloured Plates and Wood Engravings. i2mo, 6s. cloth boards. A mass of information, of use to the amateur and of value to the practical man. 1 ' English Mechanic. good know! 14 CROSBY LOCK WOOD &> CO.'S CATALOGUE. DELAMOTTES' WORKS on ILLUMINATION & ALPHABETS. A PRIMER OF THE ART OF ILLUMINATION, for the Use of Beginners : with a Rudimentary Treatise on the Art, Practical Directions for its exercise, and Examples taken from Illuminated MSS., printed in Gold and Colours. By F. DELAMOTTE. New and cheaper edition. Small 4to, 6s. orna- mental boards. . The examples of ancient MSS. recommended to the student, which, with much I sense, the author chooses from collections accessible to all, are selected with judgment and jwledge, as well as taste." Athenanm. ORNAMENTAL ALPHABETS, Ancient and Medieval, from the Eighth Century, with Numerals; including Gothic, Church-Text, large and small, German, Italian, Arabesque, Initials for Illumination, Monograms Crosses, &c. &c., for the use of Architectural and Engineering Draughtsmen, Missal Painters, Masons, Decorative Painters, Lithographers, Engravers, Carvers, &c. &c. Collected and Engraved by F. DELAMOTTE, and printed in Colours. New and Cheaper Edition. Royal 8vo, oblong, zs. 6cl. ornamental boards. 1 For those who insert enamelled sentences round gilded chalices, who blazon shop legends ovei shop-doors, who letter church walls with pithy sentences from the Decalogue, this bock will be use- ful." Athenaitm. EXAMPLES OF MODERN ALPHABETS, Plain and Ornamental; including German, Old English, Saxon, Italic, Perspective, Greek, Hebrew, Court Hand, Engrossing, Tuscan, Riband, Gothic, Rustic, and Arabesque; with several Original Designs, and an Analysis of the Roman and Old English Alphabets, large and small, and Numerals, for the use of Draughtsmen, Sur- veyors, Masons, Decorative Painters, Lithographers, Engravers, Carvers, &c. Collected and Engraved by F. DELAMOTTE, and printed in Colours. New and Cheaper Edition. Royal 8vo, oblong, zs. 6d. ornamental boards. " There is comprised in it every possible shape into which the letters of the alphabet and numerals can be formed, and the talent which has been expended in the conception of the various plain and ornamental letters is wonderful." Standard. MEDIAEVAL ALPHABETS AND INITIALS FOR ILLUMI- NATORS. By F. G. DELAMOTTE. Containing 21 Plates and Illuminated Title, printed in Gold and Colours. With an Introduction by J. WILLIS BROOKS. Fourth and cheaper edition. Small 4to, 45. ornamental boards. " A volume in which the letters of the alphabet come forth glorified in gilding and all the colours of the prism interwoven and intertwined and intermingled." Sun. THE EMBROIDERER'S BOOK OF DESIGN. Containing Initials, Emblems, Cyphers, Monograms, Ornamental Borders, Ecclesiastical Devices, Mediaeval and Modern Alphabets, and National Emblems. Col- lected by F. DELAMOTTE, and printed in Colours. Oblong royal 8vo, is. 6d. t ornamental wrapper. "The book will be of great assistance to ladies and young children who are endowed with the art of plying the needle in this most ornamental and useful pretty work." East Anglian Times. Wood Carving. INSTRUCTIONS IN WOOD-CARVING, for Amateurs; with Hints on Design. By A LADY. With Ten large Plates, 2S. 6d. in emblematic wrapper. "The handicraft of the wood-carver, so well as a book can impart it, may be learnt from ' A Lady's ' publication." Athentzum. " The directions given are plain and easily understood." English Mechanic. Glass Painting. GLASS STAINING AND THE ART OF PAINTING ON GLASS. From the German of Dr. GESSERT and EMANUEL OTTO FROMBERG. With an Appendix on THE ART OF ENAMELLING. 12010, zs. 6d. cloth limp. Letter Painting. THE ART OF LETTER PAINTING MADE EASY. By TAMES GREIG BADENOCH. With 12 full- page Engravings of Examples, is. cloth limp. "The system is a simple one, but quite original, and well worth the careful attention of letter- painters. It can be easily mastered and remembered." Building News. CARPENTRY, TIMBER, etc. 15 CARPENTRY, TIMBER, etc. Tredgold's Carpentry, partly He-ivritten and En- larged by Tarn. THE ELEMENTARY PRINCIPLES OF CARPENTRY. A Treatise on the Pressure and Equilibrium of Timber Framing, the Resist- ance of Timber, and the Construction of Floors, Arches, Bridges, Roofs, Uniting Iron and Stone with Timber, &c. To which is added an Essay on the Nature and Properties of Timber, &c., with Descriptions of the kinds of Wood used in Building; also numerous Tables of the Scantlings of Tim- ber for different purposes, the Specific Gravities of Materials, &c. By THOMAS TREDGOLD, C.E. With an Appendix of Specimens of Various Roofs of Iron and Stone, Illustrated. Seventh Edition, thoroughly revised and considerably enlarged by E. WYNDHAM TARN, M.A., Author of "The Science of Build- ing," &c. With 61 Plates, Portrait of the Author, and several Woodcuts. In one large vol., 4to, price i 55. cloth. [Just published. "Ought to be in every architect's and every builder's library." Builder. " A work whose monumental excellence must commend it wherever skilful carpentry is con- cerned. The author's principles are rather confirmed than impaired by time. The additional plates are of great intrinsic value." Building News. WoodivorJcing Machinery. WOODWORKING MACHINERY : Its Rise, Progress, and Con- struction. With Hints on the Management of Saw Mills and the Economical Conversion of Timber. Illustrated with Examples of Recent Designs by leading English, French, and American Engineers, By M. Powis BALE, A.M. Inst. C.E., M.I.M.E. Large crown 8vo, 125. 6d. cloth. " Mr. Bale is evidently an expert on the subject, and he has collected so much information that his book is all-sufficient for builders and others engaged in the conversion of timber." Architect. "The most comprehensive compendium of wood-working machinery we have seen. The author is a thorough master of his subject." Building News. " The appearance of this book at the present time will, we should think, give a considerable impetus to the onward march of the machinist engaged in the designing and manufacture of wood-working machines. It should be in the office of every wood-working factory." English Mechanic. Saiv Mills. SAW MILLS : Their Arrangement and Management, and the Economical Conversion of Timber. (Being a Companion Volume to " Wood- working Machinery.") By M. Powis BALE, A.M. Inst. C.E., M.I.M.E. With numerous Illustrations. Crown 8vo, los. 6d. cloth. "The author is favourably known by his former work on 'Woodworking Machinery," of which we were able to speak approvingly. This is a companion volume, in which the administration of a large sawing establishment is discussed, and the subject examined from a financial standpoint Hence the size, shape, order, and disposition of saw mills and the like are gone into in detail, and the course of the timber is traced from its reception to its delivery in its converted state. We could not desire a more complete or practical treatise." Builder. "We highly recommend Mr. Bale's work to the attention and perusal of all those who are en- gaged in the art of wood conversion, or who are about building or remodelling saw-mills on im- proved principles." Building News. Carpentering. THE CARPENTER'S NEW G UIDE ; or, Book of Lines for Car- penters ; comprising all the Elementary Principles essential for acquiring a knowledge of Carpentry. Founded on the late PETER NICHOLSON'S Standard Work. A New Edition, revised by ARTHUR ASHPITEL, F.S.A. Together with Practical Rules on Drawing, by GEORGE PYNS. With 74 Plates, 4to, i is. cloth. Handrailing. A PRACTICAL TREATISE ON HANDRAILING : Showing New and Simple Methods for Finding the Pitch of the Plank, Drawing the Moulds, Bevelling, Jointing-up, and Squaring the Wreath. By GEORGE COLLINGS. Illustrated with Plates and Diagrams. i2mo, is. 6d. cloth limp. Circular WorJc. CIRCULAR WORK IN CARPENTRY AND JOINERY: A Practical Treatise on Circular Work of Single and Double Curvature. By GEORGE COLLINGS, Author of " A Practical Treatise on Handrailing." Illus- trated with numerous Diagrams, izmo, 2S. 6d. cloth limp. [Just published. 16 CROSBY LOCK WOOD & CO.' S CATALOGUE. Timber Merchant's Companion. THE TIMBER MERCHANT'S AND BUILDER'S COM- PANION. Containing New and Copious Tables of the Reduced Weight and Measurement of Deals and Battens, of all sizes, from One to a Thousand Pieces, and the relative Price that each size bears per Lineal Foot to any given Price per Petersburg Standard Hundred ; the Price per Cube Foot of Square Timber to any given Price per Load of 50 Feet ; the proportionate Value of Deals and Battens by the Standard, to Square Timber by the Load of 50 Feet; the readiest mode of ascertaining the Price of Scantling per Lineal Foot of any size, to any given Figure per Cube Foot, &c. &c. By WILLIAM DOWSING. Third Edition, Revised and Corrected. Crown 8vo, 35. cloth. "Everything is as concise and clear as it can possibly be made. There can be no doubt that every timber merchant and builder ought to possess it." Hull Advertiser. "An exceedingly well-arranged, clear, and concise manual of tables for the use of all who buy or sell timber." Journal of Forestry. Practical Timber Merchant. THE PRACTICAL TIMBER MERCHANT. Being a Guide for the use of Building Contractors, Surveyors, Builders, Sec., comprising useful Tables for all purposes connected with the Timber Trade, Marks of Wood, Essay on the Strength of Timber, Remarks on the Growth of Timber, &c. By W. RICHARDSON. Fcap. 8vo, 35. 6d. cloth. " This handy manual contains much valuable information for the use of timber merchants, builders, foresters, and all others connected with the growth, sale, and manufacture of timber.' Journal of Forestry. Timber Freight BooJc. THE TIMBER MERCHANT'S, SAW MILLER'S, AND IMPORTER'S FREIGHT BOOK AND ASSISTANT. Comprising Rules, Tables, and Memoranda relating to the Timber Trade. By WILLIAM RICHARDSON Timber Broker; together with a Chapter on "Speeds of Saw Mill Machinery," by M. Powis BALE, M.I.M.E.. &c. i2mo, 33. 6d. cloth boards. " A very useful manual of rules, tables, and memoranda, relating to the timber trade. We re- commend it as a compendium of calculation to all timber measurers and merchants, and as supply- ing a real want in the trade." Building News. Tables for Packing -Case Matters. PACKING-CASE TABLES ; showing the number of Super- ficial Feet in Boxes or Packing-Cases, from six inches square and upwards. By W. RICHARDSON, Timber Broker. Oblong 4to, 35. 6d. cloth. "Invaluable labour-saving tables." Ironmonger "Will save much labour and calculation." Grocer. Superficial Measurement. THE TRADESMAN'S GUIDE TO SUPERFICIAL MEA- SUREMENT. Tables calculated from i to 200 inches in length, by i to 108 inches in breadth. For the use of Architects, Engineers, Timber Merchants, Builders &c. By JAMES HAWKINGS. Third Edition. Fcap., 35. 6d. cloth. " A useful collection of tables to facilitate rapid calculation of surfaces. The exact area of any surface of which the limits have been ascertained can be instantly determined. The book will be found of the greatest utility to all engaged in building operations." Scotsman. 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. Tiiriber 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. Second Edition, carefully revised, izmo, 35. 6d. cloth. " Everything it pretends to be : built up gradually, it leads one from a forest to a treenail, and throws in, as a makeweight, a hcst of material concerning bricks, columns, cisterns, &c." English Mechanic. MINING AND MINING INDUSTRIES. 17 MINING AND MINING INDUSTRIES. Metalliferous Mining. 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. Super-royal 8vo, 3 35. cloth. \* OPINIONS OF THE PRESS. "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. "Probably no one in this country was better qualified than Mr. Hunt for undertaking such a work. Brought into frequent and closa association during a long life time with the principal guar- dians of our mineral and metallurgical industries, he enjoyed a position exceptionally favourable for collecting the necessary information. The use which he has made of his opportunities is suffi- ciently attested by the dense mass of information crowded into the handsome volume which has just been published. ... In placing before the reader a sketch of the present position of British Mining, Mr. Hunt treats his subject so fully and illustrates it so amply that this section really forms a little treatise on practical mining. . . . The book is, in fact, a treasure-house of statistical information on mining subjects, and we know of no other work embodying so great .a mass of matter of this kind. Were this the only merit of Mr. Hunt's volume it would be sufficient to render it indispensable in the library of everyone interested in the development of the mining and metallur- gical industries of this country." Athentzum. "A mass of information not elsewhere available, and of the greatest value to those who may be interested in our great mineral 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 Journal. "The work will be for the mining industry what Dr. Percy's celebrated treatise has been for the metallurgical a book that cannot with advantage be omitted from the library." Iron and Coal Trades' Review. "The literature of mining has hitherto possessed no work approaching in importance to that which has just been published. There is much in Mr. Hunt's valuable work that every shareholder in a mine should read with close attention. The entire subject of practical mining from the first search for the lode to the latest stages of dressing the ore is dealt with in a masterly manner." Academy. Coal and Iron. THE COAL AND IRON INDUSTRIES OF THE UNITED KINGDOM. Comprising a Description of the Coal Fields, and of the Princi- pal Seams of Coal, with Returns of their Produce and its Distribution, and Analyses of Special Varieties. Also an Account of the occurrence of Iron Ores in Veins or Seams; Analyses of each Variety; and a History of the Rise and Progress of Pig Iron Manufacture since the year 1740, exhibiting the Economies introduced in the Blast Furnaces for its Production and Improve- ment. By RICHARD MEADE, Assistant Keeper of Mining Records. With Maps of the Coal Fields and Ironstone Deposits of the United Kingdom. 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 iro.i or coal trades should omit from his library." Iron and Coal Trades' Review. "An exhaustive treatise and a valuable work f reference." Mining Journal. Prospecting. 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." Small i crown 8vo, 35. 6d. cloth. [Just published. "Will supply a much felt want, especially among Colonists, in whose way are so often thrown many mineralogical specimens, the value of which it is difficult for anyone, not a specialist, to determine. The author has placed his instructions before his readers in the plainest possible terms, and his book is the best of its kind." Engineer. "How to find commercial minerals, and how to identify them they are found, are the leading points to which attention is directed. The author has manag d to pack as much practical detail into his pages as would supply material for a book three times its size." Mining Journal. " Those toilers who explore the trodden or untrodden tracks on the face of the globe will find much that is useful to them in this book." Athenaitm. 1 8 CROSBY LOCK WOOD &> CO.'S CATALOGUE. 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. Second Edition, carefully Revised. Crown 8vo, I2S. 6d. cloth. "Neither the practical miner nor the general reader interested in mines, can have a better book for his companion and his guide." Mining Journal. "The volume is one which no student of mineralogy should be without." Colliery Guardian. " We are doing our readers a service in calling their attention to this valuable work." Mining- H'orld. "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 want, for no such information has hitherto been brought together within such limited space," Athen&iim. Earthy Minerals and A TREATISE ON EARTHY AND OTPIER MINERALS AND MINING. By D. C. DAVIES, F.G.S. Uniform with, and forming a Companion Volume to, the same Author's " Metalliferous Minerals and Mining." With 76 Wood Engravings. Crown 8vo, las. 6d. cloth. "It is essentially a practical work, intended primarily for the use of practical men. . . . 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. ' The book is clearly the result of many years' careful work and thought, and 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 Re-view. "The subject matter of the volume will be found of high value by all and they are a numer- ' ous class who trade in earthy minerals." Athenccum. "Will be found of permanent value for information and reference." Iron. 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." Mining 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, xamo, 35. cloth boards. ATLAS OF ENGRAVINGS to Illustrate the above, contain- ing 235 Illustrations of Mining Tools, drawn to scale. 4to, 6s. cloth boards. "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 you ma I. Coal Mining. COAL AND COAL MINING: A Rudimentary Treatise on. By WARINGTON W. SMYTH, M.A., F.R.S., &c., Chief Inspector of the Mines of the Crown. New Edition, Revised and Corrected. With numerous Illustra- tions, izmo, 45. cloth boards. "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. By THOMAS FENWICK, Surveyor of Mines, and THOMAS BAKER, C.E. izmo, 35. cloth boards. NAVAL ARCHITECTURE, NAVIGATION, etc. 19 NAVAL ARCHITECTURE, 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.,the Engineer Surveyor in Chief, Board of Trade, the 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 2s. cloth, bevelled boards. " The author writes not only with a full acquaintance with scientific formulae and details, but a'so with a profound and fully-instructed sense of the importance to the safety of our ships and sailors of fidelity in the manufacture of cables. We heartily recommend the book to the specialists to whom it is addressed." Athentziui'.. " It contains a vast amount of valuable information. Nothing seems to be wanting to make a complete and standard work of reference on the subject." Nautical Magazine. Poclzet-BooK for Naval ArcJiitects and Shipbuilders. THE NAVAL ARCHITECT'S AND SHIPBUILDER'S POCKET-BOOK of Formula, Rules, and Tables, and Marine Engineer's and Surveyor's Handy Book of Reference. By CLEMENT MACKROW, Member of the Institution of Naval Architects, Naval Draughtsman. Third Edition, Re- vised. With numerous Diagrams, &c. Fcap., 125. 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 formubs 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. PocJcet-BooJz for Marine Engineers. A POCKET-BOOK OF USEFUL TABLES AND FOR- MULM FOR MARINE ENGINEERS. By FRANK PROCTOR A.I.N.A. Third Edition. Royal 321x10, 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 Gazette. Lighthouses. EUROPEAN LIGHTHOUSE SYSTEMS. Being a Report of a Tour of Inspection made in 1873. By Major GEORGE H. ELLIOT, Corps of Engineers, U.S.A. With 51 Engravings and 31 Woodcuts. 8vo, 2is. cloth. %* The following are published in WEALE'S RUDIMENTARY SERIES. MASTING, MAST-MAKING, AND RIGGING OF SHIPS. By ROBERT KIPPING, N.A. Fifteenth Edition. i2mo, zs. 6d. cloth boards. SAILS AND SAIL-MAKING. Eleventh Edition, Enlarged, with an Appendix. By ROBERT KIPPING, N.A. Illustrated. 12010, 35. cloth boards. NAVAL ARCHITECTURE. By TAMES PEAKE. Fifth Edition with Plates and Diagrams. i2mo, 45. cloth boards. MARINE ENGINES AND STEAM VESSELS (A Treatise on). By ROBERT MURRAY, C.E., Principal Officer to the Board of Trade for the East Coast of Scotland District. 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. i2ino, 55. cloth boards. PRACTICAL NAVIGATION. Consisting of the Sailor's Sea- Book, by JAMES GREENWOOD and W. H. ROSSER ; together with the requisite Mathematical and Nautical Tables for the Working of the Problems by HENRY LAW, C.E ,and Professor J. R. YOUNG, izmo, 75., half-bound. 20 CROSBY LOCK WOOD & CO.'S CATALOGUE. NATURAL PHILOSOPHY AND SCIENCE. 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, i2s. 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 taithlul account of these that this fresh, edition of Dr. Noad's valuable text-book is launched forth." Extract from Introduction by IV. H. freece, .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. Athen&um. "An admirable text-book for every student beginner or advanced of electricity.' Engineering. " Dr. Noad's text-book has earned for itself the reputation of a truly scientific manual for the student of electricity, and we gladly hail this new amended edition, which brings it once more to the front. Mr. Preece as reviser, with the assistance of Mr. II. R. Kempe and Mr. J. P. Edwards, has added all the practical results of recent invention and research to the admirable theoretical expositions of the author, so that the book is about as complete and advanced as it is possible fo* any book to be within the lim.ts of a text-book." Telegraphic Journal, 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. "The accounts given of electricity and galvanism are not only complete in a scientific sense, but, which is a rarer thing, are popular and interesting." Lancet. "It is worthy of a place in the library of e^ery public institution." Mining Journal. Electric Light. ELECTRIC LIGHT : Its Production and Use. Embodying Plain Directions for the Treatment of Voltaic Batteries, Electric Lamps, and Dynamo-Electric Machines. By J. W. URQVHART, C.E., Author of " Electro- plating: A Practical Handbook " Edited by F. C. WEBB, M.I.C.E , M.S.T.E. Second Edition, Revised, with large Additions and 128 Illusts. 75. 6d. cloth. " The book is by far the best that we have yet met with on the subject." Athenauim. "It is the only work at present available which gives, in language intelligible for the most par* to the ordinary reader, a general but concise history of the means which have been adopted up to> the present time in producing the electric light." Metropolitan Electric Liyliting. THE ELEMENTARY PRINCIPLES OF ELECTRIC LIGHT- ING. By ALAN A. CAMPBELL SWINTON, Associate S.T.E. Crown 8vo, is. 6d., cloth. [Just published. " As a stepping-stone to treatises of a more advanced nature, this litt'e work will be found most efficient." Bookseller. "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. Dr. Lardner's School ILandbooJts. NATURAL PHILOSOPHY FOR SCHOOLS. By Dr. LARDNER. 328 Illustrations. Sixth Edition. One Vol., 35. 6d. cloth. " A very convenient class-book for junior students in private schools. It is intended to convey, in cleat and precise terms, general notions of all the principal divisions of Physical Science." British Quarterly Review. ANIMAL PHYSIOLOGY FOR SCHOOLS. By Dr. LARDNER. With 190 Illustrations. Second Edition. One Vol., 35. 6d. cloth. " Clearly written, well ; rranged, and excellently illustrated." Gardener's Chronicle. Dr. Lardner's Electric Telegraph. THE ELECTRIC TELEGRAPH. By Dr. LARDNER. Re- vised and Re- written by E. B. BRIGHT, F.R.A.S. 140 Illustrations. Small 8vo, as. 6d. cloth. " One of the most readable books extant on the Electric Telegraph." English Mechanic- NATURAL PHILOSOPHY AND SCIENCE. 21 Storms. STORMS : Their Nature, Classification, and Laws; with the Means of Predicting them by their Embodiments, the Clouds. By WILLIAM BLASIUS. With Coloured Plates and numerous Wood Engravings. Crown 8vo, IDS. 6d. cloth. " A useful repository to meteorologists in the study of atmospherical disturbances. Will repay perusal as being the production of one who gives evidence of acute observation." Nature. The Blowpipe. THE BLOWPIPE IN CHEMISTRY, MINERALOGY, AND GEOLOGY. Containing all known Methods of Anhydrous Analysis, many Working Examples, and Instructions for Making Apparatus. By Lieut.- Colonel W. A. Ross, R.A., F.G.S. With 120 Illustrations. Crown 8vo, 3.s. 6d. cloth. "The student who goes conscientiously through the course of experimentation here laid down will gain a better insight into inorganic chemistry and mineralogy than if he had 'got up 'any of the best text-books ot the day, and passed any number of examinations." Chemical News. The Military Sciences. AIDE-MEMOIRE TO THE MILITARY SCIENCES. Framed from Contributions of Officers and others connected with the different Ser- vices. Originally edited by a Committee of the Corps of Royal Engineers. Second Edition, most carefully revised by au Officer of the Corps, with many Additions; containing nearly 350 Engravings and many hundred Woodcuts. Three Vols., royal 8vo, extra cloth boards, and lettered, 4 IDS. "A compendious encyclopedia of military knowledge, to which we are greatly indebted." Edinburgh Review. "The most comprehensive work of reference to the military and collateral sciences." Volun- teer Service Gazette. 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, 12$. Concholoay. MANUAL OF TPIE MOLLUSC A : A Treatise on Recent and Fossil Shells. By Dr. S. P. WOODWARD, A.L.S. With Appendix by RALPH TATE, A.L.S., F.G.S. With numerous Plates and 300 Woodcuts. Cloth boards, 75. 6d. "A most valuable storehouse of conchological and geological information." Hard-wicke 's Science Gossip. Astronomy. ASTRONOMY. By the late Rev. ROBERT MAIN, M.A., F.R.S., formerly Radcliffe Observer at Oxford. Third Edition, Revised and Cor- rected to the present time, by WILLIAM THYNNK LYNN, B. A., F.R.A.S., formerly of the Royal Observatory, Greenwich. i2mo, 2s. cloth limp. " A sound and simple treatise, carefully edited, and a capiial book for beginners." K'noiultdg-e. "Accurately brought down to the requirements of the present time." Educational Timts. 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. i2mo, 55. cloth boards. " The fulness of the matter has elevated the book into a manual. Its information is exhaustive 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. 22 CROSBY LOCKWOOD &> CO.' S CATALOGUE. Dr. LARDNER'S HANDBOOKS of NATURAL PHILOSOPHY. *** The following five volumes, though each is complete in itself, and to be pur- chased separately, form A COMPLETE COURSE OF NATURAL PHILOSOPHY. The style is studiously popular. It has been the author's aim to supply Manuals for the Student, the Engineer, the Artisan, and the superior classes in Schools. THE HANDBOOK OF MECHANICS. Enlarged and almost re- written by BENJAMIN LOEWY, F.R.A.S. With 378 Illustrations. Post 8vo, 6s. cloth. "The perspicuity of the original has been retained, and chapters which had become obsolete have been replaced by others of more modern character. The explanations throughout are studiously popular, and care has been taken to show the application of the various branches ol physics to the industrial arts, and to the practical business of h.e." Mining Journal. "Mr. Loewy has carefully revised the book, and brought it up to modern requirements." Nature. "Natural philosophy has had few exponents more able or better skilled in the art of popu- larising the subject than Dr. Lardner ; and Mr. Loewy is doing good service in fitting this treatise, and the others of the series, for u^.e at the present time." Scotsman. THE HANDBOOK OF HYDROSTATICS AND PNEUMATICS. New Edition, Revised and Enlarged, by BENJAMIN LOEWY, F.R.A.S. With 236 Illustrations. Post 8vo, 55. cloth. "For those 'who desire to attain an accurate knowledge of physical science without the pro- found methods of mathematical investigation,' this work is not merely Intended, but well adapted.'' Chemical News. " The volume before us has been carefully edited, augmented to near'y twice the bulk of the former edition, and all the most recent matter has been added. . . . It is a valuable text-book." Nature. "Candidates for pass examinations will find it, we think, specially suited to their requirements." English Mechanic. THE HANDBOOK OF HEAT. Edited and almost entirely re- written by BENJAMIN LOEWY, F.R.A.S., &c. 117 Illustrations. Post 8vo, 6s. cloth. " The style is always clear and precise, and conveys instruction without leaving any cloudiness or lurking doubts behind." Engineering. "A most exhaustive book on the subject on which it treats, and is so arranged that it can be understood by all who desire to attain an accurate knowledge of physical science Mr. Loewy has included all the latest discoveries in the varied laws and effects of heat." Standard. "A complete and handy text-isook for the use of students and genera! readers." English Mechanic. THE HANDBOOK OF OPTICS. ByDiONYSius LARDNER,D.C.L. formerly Professor of Natural Philosophy and Astronomy in University College, London. New Edition. Edited by T. OLVER HARDING, B.A. Lond., of University College, London. With 298 Illustrations. Small 8vo, 448 pages, 55. cloth. "Written by one of the ablest English scientific writers, beautifully and elaborately illustrated." Mechanics' Magazine. THE HANDBOOK OF ELECTRICITY, MAGNETISM, AND ACOUSTICS. By Dr. LARDNER. Ninth Thousand. Edit, by GEORGE CAREY FOSTER, B.A., F.C S. With 400 Illustrations. Small 8vo, 55. cloth. ' The book could not have been entrusted to anyone better calculated to preserve the terse and lucid style of Lardner, while correcting his errors and bringing up his work to the present state of scientific knowledge." Popular Science Review. Dr. Lardner's HandbooJc of Astronomy. THE HANDBOOK OF ASTRONOMY. Forming a Companion to the " Handbook of Natural Philosophy. ' By DIONYSIUS LARDNER, D.C.L., formerly Professor of Natural Philosophy and Astronomy in University College, London. Fourth Edition. Revised and Edited by EDWIN DUNKIN, F.R.A.S., Royal Observatory, Greenwich. With 38 Plates and upwards of 100 Woodcuts. In One Vol., small 8vo, 550 pages, 95. 6d. cloth. "Probably no other book contains the same amount of information in so compendious and well- arranged a form certainly none at the pr;ce at which thib is ottered to the public.' Athenaum. "We can do no other than pronounce this work a most valuable manual of astronomy, and we strongly recommend it to all who v, ish to acquire a general but at the same time correct acquaint- ance with this sublime science." Quarterly Journal of Science. "One of the most deservedly popular books on the subject . . . We would recommend not only the student of the elementary principles of the science, but he who aims at mastering the higher and mathematical branches of astronomy, not to be without this work beside him." Practi- cal Magazine. NATURAL PHILOSOPHY AND SCIENCE. 23 DR. LARDNER'S MUSEUM OF SCIENCE AND ART. THE MUSEUM OF SCIENCE AND ART. Edited by DIONYSIUS LARDNER, D.C.L., formerly Professor of Natural Philosophy and Astronomy in University College, London. With upwards of 1,200 Engrav- ings on Wood. In 6 Double Volumes, i is., in a new and elegant cloth bind- ing ; or handsomely bound in half-morocco, 315. 6d. Contents : The Planets: Are they Inhabited Worlds? Weather Prognostics Popular Fallacies in n " stions of Physical Science Latitudes and igitudes Lunar Influences Mete0ric Stones and Shooting Stars Railway Accidents Light Common Things: Air Locomotion in the United States Cometary Influences Common Things : Water The Potter's Art- Common Things : Fire Locomotion and Transport, their Influence and Progress The Moon Common Things: The Earth The Electric Telegraph Terrestrial Heat The Sun Earthquakes and Volcanoes Barometer, Safety Lamp, and Whitworth's Micrometric Apparatus Steam The Steam Engine The Eye The Atmosphere lime Common Things: Pumps Common Things : Spectacles, the Kaleidoscope Clocks and Watches Qu Lo motive Thermometer New Planets : Le- verrier and Adams's Planet Magnitude and Minuteness Common Things : The Almanack Optical Images How to observe the Heavens Common Things: The Looking-glass Stellar Universe The Tides Colour Com- mon Things: Man Magnifying Glasses In- stinct and intelligence The Solar Microscope The Camera Lucida The Magic Lantern The Camera Obscura The Microscope The White Ants: Their Manners and Habits The Surface of the Earth, or First Notions of Geography Science and Poetry The Bee- Steam Navigation Electro-Motive Power Thunder, Lightning, and the Aurora Borealis The Printing Press The Crust of the Earth Comets The Stereoscope The Pre-Ada- mite Earth Eclipses Sound. Microscopic Drawing and Engraving Loco- I Opinions of the Press. "This series, besides affording popular but sound instruction on scientific subjects, with which the humblest man in the country ought to be acquainted, also undertakes that teaching of 'Com- mon Things ' which every well-wisher of his kind is anxious to promote Many thousand copies of this serviceable publication have been printed, in the belief and hope that the desire lor instruction and improvement widely prevails ; and we have no fear that such enlightened faith will meet with disappointment." Times. "A cheap and interesting publication, alike informing and attractive. The papers combine subjects of importance and great scientific knowledge, considerable inductive powers, and a popular style of treatment." Spectator, "The 'Museum of Science and Art" is the most valuable contribution that has ever been made to the Scientific Instruction of every class of society." Sir DAVID BREWSTER, in the North British Re-view. Whether we consider the liberality and beauty of the illustrations, the charm of the writing 1 , or the durable interest of the matter, we must express our belief that there is hardly to be found among the new books one that would be welcomed by people of so many ages and classes as a valuable present." Examiner. \* Separate books formed from the above, suit able for Workmen's Libraries, Science Classes, &c. Common Tilings Explained. Containing Air, Earth, Fire, Water, Time, Man, the Eye, Locomotion, Colour, Clocks and Watches, &c. 233 Illus- trations, cloth gilt, 55. The Microscope. Containing Optical Images, Magnifying Glasses, Origin and Description of the Microscope, Microscopic Objects, the Solar Micro- scope, Microscopic Drawing and Engraving, &c. 147 Illustrations, cloth gilt, 2s. Popular Geology* Containing Earthquakes and Volcanoes, the Crust of the Earth, &c. 201 Illustrations, cloth gilt, zs. 6d. Popular Physics. Containing Magnitude and Minuteness, the Atmo- sphere, Meteoric Stones, Popular Fallacies, Weather Prognostics, the Thermometer, the Barometer, Sound, &c. 85 Illustrations, cloth gilt, 2S. 6d. Steam and its Uses. Including the Steam Engine, the Locomotive, and Steam Navigation. 89 Illustrations, cloth gilt, 25. Popular Astronomy. Containing How to observe the Heavens The Earth, Sun, Moon, Planets, Light, Comets, Eclipses, Astronomical Influ- ences, &c. 182 Illustrations, 45. 6d. The liee and White Ants : Their Manners and Habits. With Illustra- tions of Animal Instinct and Intelligence. 135 Illustrations, cloth gilt, 2S. The Electric Telegraph Popularised. To render intelligible to all who can Read, irrespective of any previous Scientific Acquirements, the various forms of Telegraphy in Actual Operation. 100 Illustrations, cloth gilt, is. 6d. 24 CROSBY LOCK WOOD & CO. 1 S CATALOGUE. MATHEMATICS, GEOMETRY, TABLES, etc. Practical Mathematics. MATHEMATICS FOR PRACTICAL MEN. Being a Com- mon-place Book of Pure and Mixed Mathematics. Designed chiefly for the Use of Civil Engineers, Architects and Surveyors. By OLINTHUS GREG- ORY, LL.D., F.R.A.S., Enlarged by HENRY LAW, C.E. 4th Edition, care- fully Revised by J. R. YOUNG, formerly Professor ot Mathematics, Belfast College. With 13 Plates, 8vo, i is. cloth. " The engineer or architect will here find ready to his hand rules for solving nearly every mathematical 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 oM."J>inMer. " One of the most 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. Metrical Units and Systems, etc. MODERN METROLOGY: A Manual of the Metrical Units and Systems of the Present Century. With an Appendix containing a proposed English System. By Lowis D'A. JACKSON, A.M. Inst. C.E., Author of " Aid to Survey Practice," &c. Large crown 8vo, 125. 6d. cloth. "The author has brought together much valuable and interesting information. . . . We cannot but recommend the work to the consideration of all interested in the practical reform of our weights and measures." Nature. "For exhaustive tables of equivalent weights and measures of all sorts, and for clear demonstra- tions of the effects of the various systems that have been proposed or adopted, Mr. Jackson's treatise is without a rival." Academy. The Metric System. A SERIES OF METRIC TABLES, in which the British Stand- ard Measures and Weights are compared with those of the Metric System at present in Use on the Continent. By C. H. DOWLING, C.E. 8vo, IDS. 6d. strongly bound. "Their accuracy has been certified by Professor Airy, the Astronomer-Royal." Builder. " Mr. Bowling's Tables are well put together as a ready-reckoner for the conversion of one system into the other." Athenteum Geometry for the ArcJiitect, 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 Appen- dices on Diagrams of Strains and Isometrical Projection. With 172 Illus- trations, demy 8vo, 95. cloth. "No book with the same objec's in view has ever been published in which the clearness of the rules laid down and the illustrative diagrams have been so satisfactory." Scotsman. "This is a manual for the practical man, whether architect, engineer, or mechanic. . . .The object of the author being to avoid all abstruse formute or complicated methods, and to enable persons with but a moderate knowledge of geometry to work out the problems required." English Mechanic. 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. Iron and Metal Trades 9 Calculator. THE IRON AND METAL TRADES' COMPANION. For expeditiously ascertaining the Value of any Goods bought or sold by Weight, from is. per cwt. to 1125. per cwt., and from one farthing per pound to one shilling per pound. Each Table extends from one pound to 100 tons. To which are appended Rules on Decimals, Square and Cube Root, Mensuration of Superficies and Solids, &c. ; Tables of Weights of Materials, and other Useful Memoranda. By THOS. DOWNIE. 396 pp., 95. Strongly bound leather. " A most useful set of tables, and will supply a want, for nothing like them before existed." Building News. " Although specially adapted to the iron and metal trades, the tables will be found useful in every other business in which merchandise is bought and sold by weight." Rail-way News. MATHEMATICS, GEOMETRY, TABLES, etc. 25 Calculator for Numbers and Weights Combined. THE COMBINED NUMBER AND WEIGHT CALCU- LA TOR. Containing upwards of 250,000 Separate Calculations, showing at a glance the value at 421 different rates, ranging from ^ ? th of a Penny to 2os. each, or per cwt., and "20 per ton, of any number of articles consecutively, from i to 470. Any number of cwts., qrs., and Ibs., from i cwt. to 470 cwts. Any number of tons, cwts., qrs., and Ibs., from i to 23! tons. By WILLIAM CHADWICK, Public Accountant. Imp. 8vo,3os., strongly bound. KS" This comprehensive and entirely unique and original Calculator is adapted for the use of Accountants and Auditors, Railway Companies, Canal Companies, Shippers, Shipping Agents, General Carriers, &c. Ironfounders, Brassfoittiders, Metal Merchants, Iron Manufacturers, Iron- mongers, Engineers, Machinists, Boiler Makers, Millwrights, Roofing, Bridge and Girder Makers, Colliery Proprietors, &c. Timber Merchants, Builders, Contractors, Architects, Surveyors, Auctioneers, Valuers, Brokers, Mill Owners and Manufacturers, Mill Furnishers, Merchants and General Wholesale Tradesmen. *** OPINIONS OF THE PRESS. " The book contains the answers to questions, and not simply a set of ingenious puzzle methods of arriving at results. It is as easy of reference for any answer or any number ot answers as a dictionary, and tl.e references are even more quickly made. For making up accounts or esti- mates, the book must prove invaluable to all who have any considerable quantity of calculations involving price and measure in any combination to do." Engineer. " The most complete and practical ready reckoner which it has been our fortune yet to see. It is difficult to imagine a trade or occupation in which it could not be of the greatest use, either n saving human labour or in checking work. The publishers have placed within the reach of every commercial man an invaluable and unfailing assistant." The Miller. Comprehensive Weight Calculator. THE WEIGHT CALCULATOR. Being a Series of Tables upon a New and Comprehensive Plan, exhibiting at One Reference the exact Value of any Weight from i Ib. to 15 tons, at 300 Progressive Rates, from id. to i68s. per cwt., and containing 186,000 Direct Answers, which, with their Combinations, consisting of a single addition (mostly to be performed at sight), will afford an aggregate of 10,266,000 Answers ; the whole being calcu- lated and designed to ensure correctness and promote despatch. By HENRY HARBEN, Accountant. An entirely New Edition, carefully Revised. Royal 8vo, strongly half-bound, i 53. "Of priceless value to business men. Its accuracy and completeness have secured for it a reputation which renders it quite unnecessary for us to say one word in its praise. It is a necessary book in all mercantile offices." Sheffield Independent. Comprehensive Discount Guide. THE DISCOUNT GUIDE. Comprising several Series of Tables for the use of Merchants, Manufacturers, Ironmongers, and others, by which may be ascertained the exact Profit arising from any mode of using Discounts, either in the Purchase or Sale of Goods, and the method of either Altering a Rate of Discount or Advancing a Price, so as to produce, by one operation, a sum that will realise any required profit after allowing one or more Discounts : to which are added Tables of Profit or Advance from ij to go per cent., Tables of Discount from ij to g8| per cent., and Tables of Com- miss^on, &c., from % to 10 per cent. By HENRY HARBEN, Accountant, Author of " The Weight Calculator." New Edition, carefully Revised and Corrected. Demy 8vo, 544 pp. half-bound, t 55. " A book such as this can only be appreciated by business men, to whom the saving of time means saving of money. We have the high authority of Professor J. R. Young that the tables throughout the work are constructed upon strictly accurate principles. The work must prove of great value to merchants, manufacturers, and general traders." British Trade Journal Iron Shipbuilders 9 and Iron Merchants 9 Tables. IRON -PLATE WEIGHT TABLES: For Iron Shipbuilders, Engineers and Iron Merchants. Containing the Calculated Weights of up- wards of 150,000 different sizes of Iron Plates, from i foot by 6 in. by \ in. to 10 feet by 5 feet by i in. Worked out on the basis of 40 Ibs. to the square foot of Iron of i inch in thickness. Carefully compiled and thoroughly Re- vised by H. BURLINSON and W. H. SIMPSON. Oblong 410, 255. half-bound. "This work will be found of great utility. The authors have had nvich practical experience of what is wanting in making estimates; and the use of the book M ill save much time iu making elaborate calculations." English. Mechanic. 26 CROSBY LOCKWOOD & CO.' S CATALOGUE INDUSTRIAL AND USEFUL ARTS. Soap-making. THE ART OF SOAP-MAKING: A Practical Handbook of the Manufacture of Hard and Soft Soaps, Toilet Soaps, &c. Including many New Processes, and a Chapter on the Recovery of Glycerine from Waste Leys. By ALEXANDER WATT, Author of " Electro- Metallurgy Practically Treated," &c. With numerous Illustrations. Second Edition, Revised. Crown 8vo, gs. cloth. "The work will prove very useful, not merely to the technological student, but to the practica soapboiler who wishes to understand the theory of his art." Chemical News. "It is really an excellent example of a technical manual, entering, as it does, thoroughly and exhaustively both into the theory and practice of soap manufacture." Knowledge. "Mr. Watt's book is a thoroughly practical treatise on an art which has almost no literature in our language. We congratulate the author on the success of his endeavour to fill a void iu English technical literature." Mature. Leather Manufacture. THE ART OF LEATHER MANUFACTURE. Being a Practical Handbook, in which the Operations of Tanning, Currying, and Leather Dressing are fully Described, and the Principles of Tanning Ex- plained, and many Recent Processes introduced; as also Methods for the Estimation of Tannin, and a Description of the Arts ot Glue Boiling, Gut Dressing, &c. By ALEXANDER WATT, Author of " Soap-Making," " Electro- Metallurgy," &c. With numerous Illustrations. Crown 8vo, 125. 6d. cloth. " Mr. Watt has rendered an important service to the trade, and no less to the student of technology." Chemical News. "A sound, comprehensive treatise. The book is an eminently valuable production which re- dounrts to the credit of both author and publishers." Chemical Review. "This volume is technical without being tedious, comprehensive and complete without being prosy, and it bears on every page the impress of a master hand. We have never come across a better trade treatise, nor one that so thoroughly supplied an absolute want." Shoe and Leather Trades' Chronicle. Boot and Shoe Making. TPIE ART OF BOOT AND SHOE-MAKING. A Practical Handbook, including Measurement, Last-Fitting, Cutting-Out, Closing and Making, with a Description of the most approved Machinery employed. By JOHN B. LEND, late Editor of St. Crispin, and The Boot and Shoe-Maker. With numerous Illustrations. Crown 8vo, 55. cloth. " This excellent treatise is by far the best work ever written on the subject. A new work, embracing all modern improvements, was much wanted. This want is now satisfied. The chapter on clicking, which shows how waste may be prevented, will save fifty times the price of the book." Scottish Leather Trader. Dentistry. MECHANICAL DENTISTRY: A Practical Treatise on the Construction of the various kinds of Artificial Dentures. Comprising also Use- ful Formulae, Tables and Receipts for Gold Plate, Clasps, Solders, &c. &c. By CHARLES HUNTER. Second Edition, Revised. With upwards of 100 Wood Engravings. Crown 8vo, 75. 6d. cloth. " We can strongly recommend Mr. Hunter's treatise to all students preparing for the profession of dentistry, as well as to every mechanical dentist. ' Dublin Journal of Medical Science. " A work in a concise form that few could read without gaining information from." British Journal of Dental Science. 'Breiving. A HANDBOOK FOR YOUNG BREWERS. By HERBERT EDWARDS WRIGHT, B.A. Crown 8vo, 35. 6d. cloth. " This little volume, containing such a large amount of good sense in so small a compass, o"ght to recommend itself to every brewery pupil, and many who have passed that stage." Brewers' Guardian. "The book is very clearly written, and the author has successfully brought his scientific know- ledge to bear upon the various processes and details of brewing." Breu'er. Wood Engraving. A PRACTICAL MANUAL OF WOOD ENGRAVING. With a Brief Account of the History of the Art. By WILLIAM NORMAN BROWN. With numerous Illustrations. Crown 8vo, 2s. cloth. " The author deals with the subject in a thoroughly practical and easy series of representative lessons." Pat>fr and Printing Trades' Journal. INDUSTRIAL AND USEFUL ARTS. 27 Electrolysis of Gold, Silver, Copper, CO.' S CATALOGUE. A. Complete Epitome of the Laws of this Country. EVERY MAN'S OW^ LAWYER : A Handy-book of the Principles of Law and Equity. By A BARRISTER. Twenty-third Edition. Carefully Revised and brought down to the end of the last Session, including Summaries of the Latest Statute Laws. With Notes and References to the Authorities. Crown 8vo, price 65. 8rf. (saved at every consultation), strongly bound in cloth. Comprising THE RIGHTS AND WRONGS OF INDIVIDUALS MERCANTILE AND COM- MERCIAL LAW CRIMINAL LAW PARISH LAW COUNTY COURT LAW GAME AND FISHERY LAWS POOR MEN'S LAWSUITS THE LAWS OF BANKRUPTCY BETS AND WAGERS CHEQUES, BILLS, AND NOTES CONTRACTS AND AGREEMENTS COPYRIGHT ELECTIONS AND REGISTRATION INSURANCE LIBEL AND SLANDER MARRIAGE AND DIVORCE MERCHANT SHIPPING MORTGAGES SETTLEMENTS STOCK EXCHANGE PRACTICE TRADE MARKS AND PATENTS TRESPASS NUISANCES, &c. TRANSFER OF LAND, &c. WARRANTY WILLS AND AGREEMENTS, &c. &c. Opinions of the Press. " No Englishman ought to be without this book. . . . Any person perfectly uninformed on legal matters, who may require sound information on unknown law points, will, by reference to this book, acquire the necessary information, and thus on many occasions save the expense and loss of lime of a visit to a lawyer." Engineer. " It is a complete code of English Law, written in plain language, which all can understand." Weekly Times. "A useful and concise epitome of the law, compiled with considerable care." Law Magazine. " What it professes to be a complete epitome of the laws of this country, thoroughly intelli- gible to non-professional readers. The book is a handy one to have in readiness when bome knotty point requires ready solution." Bell's Life. Metropolitan Hating Appeals. REPORTS OF APPEALS HEARD BEFORE THE COURT OF GENERAL ASSESSMENT SESSIONS, from the Year 1871 to 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. House Property. HANDBOOK OF HOUSE PROPERTY : A Popular and Practical Guide to the Purchase, Mortgage, Tenancy, and Compulsory Sale of Houses and Land. By E. L. TARBUCK, Architect and Surveyor. Third Edition, i2ino, 3S. 6d. cloth. "The advice is thoroughly practical." Law yournal. "This is a well-written and thoughtful work. We commend the work to the careful study of all interested in questions affecting houses and land." Land Agents' Record. Imvood's Estate Tables. TABLES FOR THE PURCHASING OF ESTATES, Freehold, Copyhold, or Leasehold; Annuities, Advowsons, &c., and for the Renewing ol 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. 22nd 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. I2mo, 8s. cloth. "Those interested in tne 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. " ' Inwood'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 fail to be of the utmost utility." Mining Journal. Agricultural and Tenant-Wight Variation. THE AGRICULTURAL AND TENANT-RIGHT-VALUERS ASSISTANT. By .TOM BRIGHT, Agricultural Surveyor, Author of "The Live Stock of North Devon," &c. Crown 8vo, 35. 6d. cloth. [Just published. " 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. The book is well calculated to assist the valuer in the discharge of his duty. Agricultural Gazette. J. OGDEN AND CO. 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