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Electro-Metallurgy (As that to be deposited This)

as that to be deposited. This is gradually eaten | of cyanide of potassium until no further precipiaway while the deposition is going on, on the cathode, and the solution thus kept of uniform strength. The current may be regulated by altering the distance between the poles. With the same battery power, the amount of electricity passing will be less as the distance of the poles in the electrolyte is greater. Too powerful a current must be avoided, as it renders the coating brittle and non-adherent. It should not be strong enough to cause bubbles of gas to arise from the object. A large number of objects can be plated by one battery if they are suspended on copper rods, the ends of which are connected with the pole. Smee's Cell Consists of two plates of amalgamated zinc, separated by a piece of baked and varnished wood, and between them a plate of silver having deposited on it by the electric current finely divided platinum; so as to roughen it and prevent the adhesion of hydrogen. The silver plate is fixed in the wood separating the zinc plates; to the zinc and to the silver plates are attached binding screws for the wires. The exciting fluid is dilute sulphuric acid; 1 part of acid to 20 of water, is strong enough. When more intensity is required, several cells are joined by passing wires from the anode of one cell to the cathode of the next. This form of battery is generally preferred on account of its simplicity, constancy, and ease of management. Daniell's Cell.

In delicate operations, as in copying engraved plates, where great constancy is required, this form of cell is employed. It consists of a plate of amalgamated zinc, one of copper, generally of cylindrical form separated by a cell of porous earthenware (a flower-pot with the hole closed by a cork, makes a very good porous cell). The plates and cell are enclosed in a glass or earthenware vessel; the zinc is excited by dilute sulphuric acid; the copper is kept immersed in saturated solution of sulphate of copper (blue-stone). The solution of copper is gradually decomposed; the copper being deposited in the copper plate. Hence there should always be a quantity of crystals of the sulphate at the bottom of the cell, and the solution should be stirred from time to time; or the crystals may be suspended in a basket near the top of the solution.

Nitric Acid Batteries.

When great intensity is required, as in the deposition of copper on iron, and of certain alloys, the decomposition of fused chlorides for the pur-- pose of obtaining certain metals, these batteries are used. In all cases the positive plate is of amalgamated zinc excited by dilute sulphuric acid; which may be as strong as 1 in 10 with 1-10th of nitric acid. This is separated by a porous cell from the negative plate, which may be of platinum (Grove), carbon (Bunsen), or passive iron (Callan). The negative plate is immersed in strong nitric acid. Iron may be rendered passive by dipping it once or twice into strong nitric acid, and then washing with water and carefully drying.

To Prepare Articles for Plating.

Wash in weak lye to remove grease. Dip into dilute nitric acid to remove oxide. Scour with a hard brush and fine sand. Then having fastened to a wire, dip in strong nitric acid and immerse in the electrolyte as quickly as possible.

Solution for Silvering.

Add to a solution of nitrate of silver (made by dissolving silver in pure nitric acid), a solution tate is formed; but not enough to re-dissolve the precipitate already thrown down. Pour off the supernatant liquid, wash with water, and then re-dissolve the precipitate in cyanide of potassium. The anode should be of silver. Should the solution change on keeping, add a little fresh cyanide. Use a moderate current. An ounce and a half of silver will give to a surface a foot square, a coating as thick as common writing-paper. And since silver is worth $1.25 per ounce, the value of the silver covering a foot square, would be about $1.87. At this rate, a well plated tea-pot or coffeepot is plated at a cost in silver of not more than $1.50 to $2. The other expenses, including labor, would hardly be more than half that amount.

To Recover the Silver from a Bath.

Add muriatic acid, carefully avoiding the fumes which are given off. Dilute the liquid, decant from the precipitate formed, dry the precipitate, and reduce in a black lead crucible with carbonate of soda.

Solution for Gilding.

Electro-gilding is done in like manner. The gold is dissolved in nitro-hydrochloric acid, washed with boiling nitric acid, and then digested with calcined magnesia. The gold is deposited in the form of an oxide, which after being washed in boiling nitric acid, is dissolved in cyanide of potassium, in which solution the articles to be plated with gold, after due preparation, are placed. Iron, steel, lead, and some other metals that do not readily receive the gold deposit, require to be first lightly plated with copper, or dipped in a solution of nitrate of siver, 1 part; nitrate of mercury, 1 part; nitric acid (s. g. 1.384) 4 parts; water, 120 parts. The positive plate of the battery must be of gold, the other plate of iron or copper. The process is the same as that above described; use a feeble current.

A The popular notion is, that genuine electrogilding must necessarily add a good deal to the cost of the article plated. This is erroneous. silver thimble may be so handsomely plated as to have the appearance of being all gold for 5 cents, a pencil-case for 20 cents, and a watch-case for 1 dollar. An estimate of the relative value of electro-gilding, as compared with silver-plating, considering the cost of material alone, is about 15 to 1. To Deposit Brass.

Dissolve 5 oz. powdered acetate of copper in gall. of water, add 1 pt. of solution of arzenia.

Dissolve 10 oz. sulphate of zinc (white vitrio.) en 1 gall. of water, at 180° Fahr., and when cool add 1 pt. of solution of ammonia. Dissolve 4 lbs. potassa in 1 gall. of water. Lastly, dissolve 8 oz. cyanide of potassium in 1 gall. of hot water. Mix in the following order: add the copper solution to that of zinc, then the potash and cyanide, digest for an hour or so, and add water to make up 8 gall. Work with a brass anode and an active battery power, occasionally adding more ammonia and cyanide.

To Copy Medals.

Casts of the medals may be made in fusible metal, plaster, wax, etc. In case of a non-metallic mould it must have its face brushed over with black lead. The metallic mould is to be coated on the back with wax or varnish. The wire is A usually attached to the edge by soldering or twisting. A decomposing cell is not necessary. water-tight box is divided by a porous (plaster or leather) partition. On one side is a plate of zinc immersed in diluted, 1 to 20, sulphuric acid; on the other a solution, kept saturated, of sulphate of copper. A wire from the zinc is attached to a copper rod, from which the medals are suspended, which consists simply in depositing copper upon dipping into the copper solution.

To Bronze Copper Medals. 1. Brown. -Moisten the surface, well cleaned, with weak nitric acid, allow it to dry, and apply a gentle heat. 2. Black. - Use, instead of nitric acid, sulphydrate of ammonia or liver of sulphur. 3. Green. - Expose in a close box to the fumes of chloride of lime, or to the vapor of acetic or muriatic acid. 4. For bronzing all sorts of fine copper or brass work a weak solution of bichloride of platinum is used. By varying the temperature and color, between a steel gray and deep black may be obtained.

To Deposit Copper on Iron.

Prepare a solution of cyanide of copper, by dissolving oxide of copper in cyanide of potassium, or by adding cyanide of potassium to a solution of sulphate of copper, and re-dissolving the precipitate formed. Work with a strong battery power. The copper will not deposit unless the current be strong enough to evolve hydrogen at the cathode, which evolution should always be avoided in depositing the other metals.

Voltaic Protection of Metals.

When two metals are united and exposed to a corrosive agent, which would act unequally upon them if separate, the one which would be most acted on receives most of the force of the corrosion, while the other escapes. Thus iron coated with zinc (galvanized iron) will last for years exposed to the atmosphere. Copper points on lightningrods remain bright for a long time, when screwed into a zinc ball.

Coating Electrotype-plates with Iron.

The following has been successfully employed in coating electrotype deposits with a coating of pure iron, thereby rendering them little inferior to steel-plate engravings as regards durability:

Dissolve 1 lb. of sal ammoniac in 1 gall. of rainwater, then add 2 lbs. of neutral acetate of iron; boil the solution in an iron-kettle for 2 hours, replacing the water lost by evaporation; when cold, filter the solution, and keep it in close-covered vats (when not in use) to prevent oxidation.

The iron plate used in the decomposition-cell must be of the same surface as the plate to be coated with iron; a Smee's battery, of at least 3 cells, charged with 1 part sulphuric acid, and 60 parts water, being used for the decomposition.

To insure success the following rules must be observed: 1st. The plate must be thoroughly freed from any greasy matter by immersing in a solution of caustic soda, then rinsed in clean cold rainwater, after which dip it in dilute acetic acid, and immediately transfer it to the solution of iron; this will insure perfect adhesion between the metals. 2nd. The solution must be filtered previous to use to remove the oxide of iron formed by exposure to the atmosphere. After the plates have been coated with iron they must be well rinsed in clear warm rain-water, then in a weak alkaline solution, well dried with a piece of clean soft cotton, and slightly oiled to prevent oxidation. The coating of iron is very hard and brittle, resembling the white iron used by manufacturers of malleable iron. Should any of the surface be damaged, the whole coating of iron may be removed by immersion in dilute sulphuric acid, and re-coated again by the above process.

Copper Tubes made by Galvanic Process.

Le Génie Industrial publishes the details of a process for making copper-tubes without soldering, lead patterns by the galvanic battery, and then melting out the lead. It is said to work perfectly, and of course tubes could be made of any desired form-straight, curved, or right-angled. This suggests the idea of forming tubes in the same manner with cores of wax or clay. The clay may be forced into the size of the pipe through a drawplate, then allowed to harden slightly, when it may be covered with plumbago and an electrodeposit of copper made upon it with a galvanic battery. When the copper is deposited in sufficient thickness the clay may be removed from the interior by boiling the pipe in water. To conduct this manufacture it would require long depositingtroughs, and the expense would probably be too great for making straight copper-tubes; but for curved tubes, such as the worms of stills, it would perhaps pay. Curved copper-tubes are commonly made by filling straight tubes with hot resin, then twisting the entire tube into its curved form.

When the resin becomes cool it is driven out by striking the pipe, which breaks the resin-core into small pieces.