ing from one-tenth to one-twentieth of sulphuric acid, then rinsed in plenty of warm water, and, when necessary, brushed with a stiff brush and pumice-stone dust, or scratch-brushed. This last operation is especially useful when parts have been united with tin solder, which becomes black and dull by the alkaline and acid baths. Another method is to dip the articles rapidly into cold mixture of sulphuric acid, 100 parts; nitric acid, 100; common salt, 1 per cent.; and quickly rinse in cold water perfectly free from copper salt, which will blacken the zinc. If, instead of quickly cleansing the zinc, it is allowed to remain a little longer in the mixture, it acquires a dead lustre which may be utilized for producing contrasts between the various parts of the same ornament. The dead lustre will become a bright one, if the object is quickly plunged in several times, and rinsed as often, in the same compound acids. It often happens that the lines of tin or lead solder are black after being dipped into the acid bath; it is then sufficient to scratch-brush before placing the object in the electroplating solution. Zinc may be slightly amalgamated with the solution of nitrate of binoxide of mercury; this increases the adherence of the electro deposits. It is often necessary, from some defect in cleansing, or in electroplating, which impairs the adherence of the deposits, to do the work over again. In such a case, remove the copper entirely by plunging the object into aquafortis and soot, until it appears black. Another dipping into the compound acids will render it perfectly clean and white, and ready to receive a new deposit.

CLEANSING LEAD AND TIN.-Tin, lead, and the alloys of these metals, are much more difficult to cleanse than zinc. A rapid scouring with potash lye, and a rubbing with a hard substance are the only means of effecting this. The objects are sometimes plunged into diluted hydrochloric acid; but the first operation is nearly always necessary. Notwithstanding the greatest care, the direct deposit of the precious metals is difficult, and does not adhere well. The results are much better if a coat of pure copper

or brass is interposed between the low metal, and the gold or silver.

CLEANSING CAST IRON.-Cast iron is cleansed by being immersed for 2 or 3 hours in water containing one-hundredth part of sulphuric acid; the metal is afterwards rinsed in cold water, and scoured with sharp sand and a fibre brush, or a coarse rag; then put again in the acid pickle, rinsed, and plunged into the electro bath. If more than 1 per cent. of sulphuric acid is added to the water, the length of the immersion must be shortened, otherwise the cast iron will be deeply corroded, and the carbon of the metal, which is insoluble in the pickle, will with great difficulty be removed by the friction of the sand. Cast iron does not gild or silver well, by a direct deposit of the precious metals. Copper or brass deposits are better, although far from perfect; but if cast iron is tinned, the coat is adherent, and will afterwards receive copper, brass, gold, or silver, if desired. If it is desired to keep cast iron already cleansed for some time before electroplating it, it is necessary to preserve it in a liquor rendered alkaline by caustic lime, potash, or soda, or their carbonates; but caustic lime-water is the cheapest and most easy method, and cast iron which has remained in it for a few hours will not rust after a long exposure to a damp atmosphere.

CLEANSING WROUGHT IRON. The cleansing of wrought iron is effected in the same manner as cast iron, but will bear a stronger pickle and a longer immersion. We refer in this place to ordinary wrought iron covered with a film of black magnetic scale or of red rust. Whitened, filed, or polished iron must be treated like steel.

CLEANSING STEEL.-Polished articles of steel, or iron, must be first cleansed in a boiling solution of caustic lye, and rubbed with pumice-stone dust, which scratches the polish slightly, and thus produces a better hold for the metals afterwards to be deposited. They are then rapidly passed through a bath composed of water, 1 quart; hydrochloric acid, 12 oz.; or sulphuric acid, 4 oz.; rinsed in cold water, and plunged into

the electroplating solution. Carefully avoid substituting nitric acid for the hydrochloric or sulphuric acid, of the above acid bath. Iron and steel may be well gilt, without an intermediary coat, in hot gilding baths. Silvering directly upon steel or iron is always imperfect and without adherence; it is therefore customary to interpose a coat of copper or brass, which renders the further operation of silver plating easy.

GALVANIC BATTERIES.-There are two kinds of batteries used for electro-deposition; those which act under the action of physical agents; but these, on account of their feeble intensity, are rarely used. Others act under the influence of chemical reactions, of decompositions and recompositions, or of greater or less affinities. The varieties of these instruments are, at the present time, very numerous. But the best battery is that which, under the smallest volume, is the most energetic, constant, regular, and economical.

Daniell's Battery.-This battery develops a constant and lasting current, but is wanting in intensity. It is especially adapted to slow deposits, which must be thick and of uniform texture. A great advantage of this battery is, that it will work without acids, and therefore without the production of gases or smell, and can be used in a private apartment without inconveni

ence.

The vase for the battery is a flat vessel of pure copper, which is half filled with a saturated solution of sulphate of copper, into which is placed a bag of canvas or a cell of porous procelain or earthenware, which causes the solution of sulphate of copper to rise to about 1 in. from the top of the copper vessel. The bag or cell is filled with a saturated solution of common salt, in which a well-cleansed zinc plate is placed. It is necessary that the levels of the two solutions should be nearly the same. If there is any difference, the solution of chloride of sodium should be slightly above the other, because if the solution of sulphate of copper passes into the porous cell, the zinc is immediately corroded, and blackened, and the battery may cease to work. When one of

Daniell's elements only is used, which seldom happens, on account of the feeble intensity of the current, the conducting wire which supports the article to be galvanized is connected with the zinc piate by a binding screw of brass, and the other wire supporting the anode is connected with the copper of the exterior vase. The solution of sulphate of copper must be kept constantly saturated with crystals of this salt, enclosed in a bag of linen or hair cloth. A similar process may be employed to keep the solution of common salt in a state of saturation. A battery thus arranged may be kept in operation for three weeks, or a month. When this battery is working, the copper of the decomposed sulphate is deposited upon the copper of the vessel, which thus increases in weight and in value. The zinc is slowly dissolved in the solution of common salt, and forms a double chloride of sodium and zinc. When a number of the elements of a Daniell's battery are to be joined together, the zinc of the first element is connected with the copper of the second by means of a well-cleansed metallic ribbon, then the zinc of the second with the copper of the third, and so on, until the whole apparatus presents at one end a copper vase, and at the other a zinc plate, unconnected. metallic wire connects the anode with the copper end, and a similar wire is bound to the zinc end, and supports the object to be electroplated. Another battery used by the electro-gilders of watch parts and by telegraphers, is composed of a cylindrical vase of stoneware, glass, or porcelain; a cylinder of zinc to which is soldered a ribbon of pure copper; a porous clay cell, and a glass balloon with a short neck, and filled with crystals of sulphate of copper. It is closed with a cork perforated with two holes, or having two notches cut along its sides. The rolled zinc plate is put into the stoneware pot, and the porous cell inside the zinc. The copper ribbon of the zinc of the first element dips on to the bottom of the cell of the next element, in such a manner that, when several elements are connected together,

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there is at one end the ribbon of zinc plate, and at the other end a copper ribbon put into the cell. Then the porous cell and the stoneware pot are filled to the same level with water. The balloon containing the crystallized sulphate of copper receives as much water as it can hold, and the notched cork being put in place, the balloon is quickly inverted with its neck in the water of the porous cell. The battery is ready to work 24 hours after. The ribbon of the zinc end is connected with the objects to be electroplated, and that of the other cell end, with the soluble anode. The sulphate of copper contained in the balloon is dissolved in the water around it, and as this solution is denser than water it falls into the porous cells through one of the notches of the cork, while an equal quantity of purer and lighter water ascends through the other notch, and so on, producing a circuit of denser liquor falling by one notch, and of lighter liquor rising by the other. The solution of sulphate of copper is decomposed in the porous cell; the sulphuric acid passes through the cell by outward pressure and acts upon the zinc, and at the same time the copper becomes deposited upon the copper ribbon connected with the zinc of the former element. In order that this battery may work regularly for 6 or 7 months, it is sufficient to replace the evaporated water. The balloon ought to contain at least 2 lbs. of sulphate of copper, and the zinc to be about 7 in. in height, and from 4 to 4 in. in diameter. The zinc may be amalgamated, in which case the action is a little slow at the start, but more regular afterwards. The copper ribbon receives all the metal of the decomposed sulphate, and it sometimes happens that part of the copper becomes deposited upon the porous cell, which must then be cleaned in aquafortis. When all the sulphate of copper is used up, the balloons are filled with a fresh quantity of crystals and new copper ribbons inserted to take the place of those rendered too voluminous. If it be desired to start the battery with a balloon immediately, add a small quantity of sulphuric acid, or of common

salt, to the water in which the zinc is placed.

Bunsen's Battery.-Each element is composed of a glass vessel which is half filled with nitric acid at 36° or 40° Baumé, and which receives a hollow cylinder of pulverized coke, moulded and cemented at a high temperature, by sugar, gum, or tar. At the upper part

of this cylinder, where it does not dip into the acid, a copper collar is fixed, which may be tightened at will by means of a screw. A copper band or ribbon is fixed to the collar, and may be connected with the zinc of another element. A porous porcelain cell is placed inside the coke cylinder, and contains a diluted solution of sulphuric acid, 1 part acid and 9 parts water, into which is put a bar or cylinder of zinc strongly amalgamated, or covered with mercury. When a battery of several elements is to be formed, the coke of the first element is connected with the zinc of the second, and so on, and the apparatus is completed, at one end, by coke communicating with the anode, and at the other, by a zinc connected with the cathode, or object to be electroplated. In this apparatus the surface of the carbon is much greater than that of the zinc; this is a wrong disposition, since, generally, the intensity of the current is in direct ratio with the surface of the zinc corroded, provided that this surface be opposite and parallel to that of the carbon.

Bunsen's Battery modified by Arche reau. This battery is preferred by gold and silver electroplaters. Each element is composed of an exterior vessel or pot, most generally of stoneware; a cylinder of zinc, covered with mercury, provided with a binding screw, or with a copper band, whether for a single element, or for the end of a combination of elements in a battery, or to connect the zinc with the carbon of another element. A porous cell of earthenware pipe or porcelain. A cylinder of graphite, made from the residue found in old gas retorts. The graphite is bound by a copper band fixed to it by means of a wire of the same metal, all the binding being afterwards covered with a