ELECTRO METALLURGY. By this elegant art the most exact copies of any natural or artificial object can be obtained, or the surface of any body non-metallic or metal may become coated with a thin layer or film of copper, gold, and silver, or a few other metals. The practionl de tails of the arrangement is all that can find a space in these pages.
On the Forms and Arrangement of Ap the deposition of metals where voltaic electricity is thepower em ployed, there are two aeso•ptions of ar rangement: the first where the surface on which the deposit is formed is itself a part of the apparatus whence the power is generated ; the other in which the ob . ject receiving the deposit forms no part of the apparatus, but where the power is procured from a battery; the former is termed the single cell, the latter the bat tery process. The forms of voltaic bat teries used are numerous, and in most cases known by the names of their re spective inventors ; such as Daniell's, Smee's, and Grove's batteries. The stant battery of Professor Daniell will be found most generally useful ; it is termed constant from its possessing the power of continuing in action for any lengthened period : it may be made in various forms, and consists of a copper cell, dividedinto two parts by a porous diaphragm or tition, which may be formed of wood, paper, plaster of Paris, earthenware, or animal membrane. The cuter cell is filled with a saturated solution of phate of copper, a perforated shelf plied with crystals of this salt is placed at the upper portion, as that part of the solution is soonest weakened, the cific gravity retaining the stronger tion below. The inner cell is filled with water, to which a few drops of sulphuric acid are added, and in which a rod or plate of amalgamated zinc is placed, to which, and to the copper of the outer cell, wires are attached. This battery may be generally employed for the poses of plating, gilding, and platinizing, and is one of the most economical modes of reducing copper. The simplest form of apparatus used for the deposition of me- tal, more particularly copper, is the single cell ; it resembles in the number of its parts a Daniell's battery ; the surface to be deposited on senting the copper of the outer cell. The diaphragm may be formed of plaster of Paris, brown paper, or thin wood ; but the action is almost rapid when the diaphragm is thinnest ; if a mould of metal or other stance be attached to the zinc in the cell containing the acid and water, and duced into the phate solution, if the metallic tion between the mould and the zinc be complete, after a short immersion the former will become coated with a sition of metallic copper, which goes on increasing in thickness as long as the strength of the cupreous solution is kept up, which may be done by placing a few crystals of sulphate in the tion. Within a few months past,
neto-electric machines have been ployed for the deposition of metals ; and in Birmingham, plating is carried on to a considerable extent hy machines, formed by peculiar arrangements of compound magnets, one of which, lately manufac tured by Mr. Woolrich, is capable of de positing from 300 to 500 ounces of silver per week ; but as such machines are dif ficult in management, and expensive in construction, they are not well suited for the purposes of experiment.
On the production of .Moulds.—Moulds may be formed either of metallic or non metallic substances ; in the latter case it is absolutely necessary that the surface of the mould submitted for deposition should be a conductor of electricity, and the best conductors are metals and car bon. Moulds for small object.), as coins or medals, may readily be made of lead or fusible metal : a very simple plan is to place the object between two strips of the former metal, scraped perfectly clean, subjecting the whole to the action of a press. Moulds may be formed of wax, stearine, tallow, plaster of Paris, sealing wax, &c., &c.: the surfaces of either of these materials may be covered with good plumbago, after fixing a metal wire into the mould to be deposited on ; the pow der should be rubbed lightly over with a soft brush, taking care that it adheres to all parts. The deposition takes place at the wire by which the article is con nected with the battery or cell, And spreads gradually from that point till the whole surface is covered ; but this pro cess is limited to the deposition of cop per only, as gold and silver will not spread to any extent on a black-leaded surface. Wood may be prepared to re ceive a deposit in the following manner : —The surface of the block or piece in tended to be deposited on is dipped in a weak solution of nitrate of silver, con tained in a fiat vessel, remaining for a few minutes in order that by capillary attraction the nitrate of silver may be drawn into the wood: a small portion of a solution of phosphorus in spirits of turpentine being poured into a watch glass, and placed on a sand-bath, is al lowed gradually to evaporate ; on hold ing the surface of the wood over the va por an immediate change occurs, the nitrate of silver is converted into metallic silver, and the object may at once be placed in the battery to receive a deposit of copper. In this manner the interior of a plaster mould may be rendered a conductor ; but as this plan can only be adopted with substances which can be wetted with the solution of nitrate of sil ver, an improvement has lately been in troduced, by the adoption of a solution of phosphorus instead of the vapor of that substance. The best known solu tion is bisulphurct of carbon, which easily dissolves a considerable portion of phos phorus.