mended, and allowed to dry. If a green gold powder be desired, mix silver foil with the gold cuttings. An addition of rose copper foil produces a red gold. The preparation is the same for silver powder employed for mending slight defects in silver articles not exposed to friction.

GOLD ELECTROPLATING.-It is not always necessary in electrogilding to use a battery, for the contact of two heterogeneous vessels, especially within a salt or acid liquor, is enough to produce electricity; thus it is sufficient to plunge the articles, attached by zinc wires, into gold baths prepared for the use of batteries, to have the operation taking place in the same manner as with a separate battery. Electrogild

moniac, 2; saltpetre, . Heat carefully | upon a gentle fire; when all the gold has disappeared, pour the cooled contents of the flask into a flat-bottomed stoneware pan. Into this liquor, place one upon the other, and in sufficient quantity, squares of linen cloth, strike them with a glass rod, in order that they may equally absorb the chloride of gold. Each square of cloth is taken out with wooden pincers, well drained, and spread for drying in a dark chamber. When nearly dry, each piece of cloth, supported upon glass rods, is placed on top of a charcoal fire, and soon takes fire. The combustion is aided by the presence of the saltpetre, and is finisned upon a marble slab. Grind the ashes under a muller, collect and keep them between the folds of a parchment leaf, arounding in the cold is employed for large which a wet cloth has been folded. The powder is then ready to use; mix it upon a slab with a few drops of water, and with this paste rub the well-cleaned surfaces of the silver to be gilt. The smooth surfaces are rubbed with the thumb, the fillets or grooves with a fine cork cut to the proper shape, and the corners or angles with a stick of soft wood, such as linden or poplar; the articles are then burnished. This gilding is very thin, but quite resisting, especially after the action of the burnishing tool, which forces the gold into the pores of the silver. If a red shade be desired, add a small proportion of pure copper to the gold to be dissolved in aqua regia.

Gilding with the Brush or with Shell Gold. The gold powder is prepared by rubbing the cuttings of gold-beaters' foil under the muller; to prevent them from being blown away, add a small quantity of white honey. When fine enough put the paste into water, by which the honey is dissolved. After several washings, settlings, and decantings, allow the powder to dry. In case of hurry, the washing may be performed upon a paper filter. The dry powder is again ground with a little gummy water, and the paste spread over the in side of a mussel-shell. The gold powder is mixed with gum water, and applied with a brush upon the parts to be

pieces, such as clocks; whilst electrogilding by heat is more adapted to the gilding of small articles, such as forks and spoons. The deposits produced by hot gilding are more smooth and clean, the colour is deeper, and the articles when removed from the bath may not require colouring; and with the same quantity of gold, gilding by heat is much more durable than that obtained from cold baths. Steel, tin, or lead can be gilt in hot baths, but not in cold.

Gold Electrogilding Baths. — 1. Distilled water, 24 gallons; cyanide of potassium, ordinary 70 per cent., 10 oz.. pure gold, 3 oz.; aqua ammonia, 17 oz. Heat the gold in a glass flask with 9 oz. of pure hydrochloric acid, and 4 oz. of pure nitric acid. When the gold is dissolved, continue the heat in order to expel the acid fumes, and until the colour of the liquid is dark red, nearly black. Remove from the fire, and dissolve the crystalline mass formed in cooling in 3 or 4 pints of water, and pour into a large porcelain dish. Add the ammonia, which produces an abundant yellow precipitate of gold ammonium; pour upon filtering paper, and the filtered liquid, which still contains traces of gold, is kept with the saved waste. Wash the precipitate remaining upon the filter several times

of time. 3. Yellow prussiate of potash, 7 oz.; pure carbonate of potash, 5 oz. sal ammoniac, 1 oz.; pure gold transformed into chloride, oz.; water, 24 gallons. Boil all the salts together, less the chloride of gold, separate by filtration the precipitate of carbonate of iron, then add the chloride of gold dissolved in a little water, and allow the bath to cool off. Any kind of gold salt, and the oxide, or even finely-powdered metal, may take the place of the chloride of gold; but the latter is preferred on account of the facility of its preparation, and of its solubility. Any kind of gold salt will be transformed into cyanide by the cyanide of potassium. The small proportion of the chloride of potassium resulting from the transformation of the chloride of gold into cyanide does not prevent the good working of the baths. The addition of a little

with cold water, until it no longer smells of ammonia. It must not be dried, as it is a fulminating mixture, and consequently very dangerous. Next dissolve in the vessel used as a bath the cyanide of potassium in the distilled water. Filter, and add the wet gold ammonium, which rapidly dissolves when stirred, and forms a clear gold bath. But before using it cold, the ammonia should be expelled by boiling for about one hour. For a newly-prepared cold electrogilding bath, the ordinary cyanide of potassium is preferable, on account of the potash it contains, which renders the iquor a better conductor of electricity. But for the preservation of the strength, the pure cyanide is better, as it possesses the advantage of a constant composition, and does not load the solution with foreign salts. The gold solution for maintaining the metallic strength of the bath is pre-prussic acid produces a brighter, but pared as follows;-Transform the gold into precipitate of gold ammonium, as above described, place it in water, 2 pints of water to 4 oz. of gold, then add cyanide of potassium until the liquor is colourless. If there is not sufficient water with the gold ammonium, the liquor will be dark red, and will not be decolourized by cyanide. 2. Distilled water, 2 gallons; cyanide of potassium, pure, 7 oz.; or ordinary cyanide, according to strength, 10 to 14 oz.; pure gold, 3 oz. Make a neutral chloride of gold, as in the preceding formula, and, when cold and crystallized, dissolve it in 3 pints of water. Filter if needed. Dissolve the cyanide in 14 pints of water, filter, and mix the two solutions, which become colourless. When it is possible to boil this bath for half an hour before using it, it becomes a better conductor of electricity, and the gilding is more uniform. Its strength is maintained by additions of neutral chloride of gold and pure cyanide of potassium, from 1 to 12 of pure cyanide to 1 of gold. Both the above baths may be diluted with once or twice their volume of water; the gilding will remain fine, but the proportion of gold deposited will be less in a given length

thinner, gilding. The indicated cyanides may be replaced by the cyanides of sodium, calcium, and ammonium. Cold gilding baths are generally kept in porcelain or stoneware vessels; but for large volumes of liquor use wooden troughs lined with gutta-percha plates. The sides of the troughs support anodes of laminated gold, which dip entirely into the liquor, and are held by small platinum wires; they are connected with the positive pole of the battery. Suspend the articles by means of metallic slinging wires to a movable frame of clean brass rods connected with the negative pole. The deposit of gold should be pure yellow, but it has sometimes a dull earthy grey colour. In that case scratch-brush it with the greatest care, and then pass it through the ormolu colouring. The gold anode conducts the electricity, and also maintains the metallic strength of the bath up to a certain point; but it is necessary to add now and then either the oxide or the chloride of gold, and a certain proportion of cyanide of potassium, to make up for that transformed intu carbonate of potash and cyanide of ammonia. The proportion of cyanide s about double that of the chloride of

the weight of the chloride, if the proper amount of gold is dissolved in aqua regia. Ten parts of metallic gold corresponds to about 18 parts of neutral chloride, or to 23 or 22 parts of acid chloride such as is usually sold. Steel articles, after cleansing by alkalies, must be passed rapidly through a very diluted solution of hydrochloric acid, wiped, and dipped into a very hot bath with an intense galvanic current at the beginning, which is gradually diminished by partly withdrawing the platinum anode. Small articles of steel, such as pens, or watch hands, are threaded on a thin brass wire, and separated one from the other by glass beads. After cleansing, they are put into the boiling bath, rinsed, dried, and polished in hot and dry saw-dust. It is preferable to give zinc, tin, lead, antimony, or the alloys of these metals, a previous coat of copper, or to begin the gilding in a hot gold electro-bath, nearly worn out, and to scratch-brush the articles carefully. The gilding is completed in a new hot bath, with a strong

solution of bisulphite and of cyanide. The whole liquor soon becomes colcurless; the bath is then ready. If the chloride of gold were thrown into the solution of phosphate of soda while hot, there would be danger of a partial reduction of the gold in the form of a metallic powder. The hot electrogilding baths for small quantities of liquor are kept in porcelain dishes, but for large baths use ename.led cast-iron kettles. The temperature may vary from 120° to 175° Fahr. Small articles, such as jewellery, are kept in the right hand with the conducting wire, and plunged and agitated in the bath. The left hand holds the anode of platinum wire, which is steeped more or less in the liquor, according to the surface of the articles to be gilt. Large picces are suspended to one or more brass rods, and are not moved about. The gilding is very rapid, and a sufficient thickness is obtained after a few minutes. The shade of the gold deposit is modified by the amount of the platinum anode dipping into the liquor. If it dips but a little, relatively to the surface of the Preparation of the Gold Bath.-1. Put articles, the gilding is pale; by immersfour-fifths of the distilled water into a ing it more the shade will become deeper porcelain dish, or an enamelled cast-iron and deeper, until it is red. The plakettle, heated over a charcoal stove, and tinum anode is connected by a conductdissolve in it, by the aid of stirring, the ing wire to the positive pole of the batcrystallized phosphate of soda. When tery, and the conducting wire starting this is entirely dissolved, remove the from the negative pole, touches or supliquor from the fire, filter if necessary, ports the articles to be gilt. As a and allow it to cool off. 2. Place the rule, it is preferable to replace the imgold in a glass flask, with oz. of pure poverished baths by fresh ones, instead of nitric acid and 1 oz. of pure hydro- keeping up their strength by additions chloric acid. Heat slowly until the of metal, especially for small articles. gold has dissolved, and then more rapidly When gilding large pieces, maintain the to expel the excess of acid. There strength of the baths by successive adshould remain a thick liquid of a black-ditions of chloride of gold, or, what is ish-red colour. Remove the flask from the fire, and by cooling the contents form a brown-red crystalline mass. The cooling is important. 3. Dissolve in a porcelain dish, in half the remaining water, the bisulphite of soda and the cyanide of potassium. 4. Then dissolve the neutral chloride of gold in the remaining water, and pour it slowly, stirring with a glass rod, into the cold solution of phosphate of soda; add the

current.

better, of equal parts of gold ammonium and pure cyanide of potassium. In this manner baths may be made to last a long time, but they are open to the inconvenience of furnishing a red or green gilding, if many articles of copper or of silver have been gilt in them. Articles

of

copper, or its alloys, should be perfectly cleansed, nd may be passed through a very diluted solution of nitrate cf binoxide of mercury. Silver