When the bath is not in use, the gold anode must be remo ed from it, otherwise it will be dissolved. If the anode were partly immersed in the bath, it would be rapidly cut at the level of the liquid; for this reason use platinum wires, which are not acted upon. It is remarkable that the solution of cyanides, even without the action of the electric current, rapidly dissolve all the metals except platinum in the cold or at a moderate temperature, and that at the boiling point they have scarcely any action upon the metals. (e) Cold electrogilding should be done slowly; and it is necessary to often look at the pieces in the bath, and scratch-brush those with an irregular deposit, or with dark spots. The intensity of the current should be often changed by increasing or diminishing the number of the elements, or the strength or the volume of the liquors in the battery. With too much intensity in the current, the deposit is black or red; it is yellow with the proper amount of electricity. With a weak current those portions opposite the anode only get covered with gold; it is well to change the position of the objects often, in order that the deposit be regular. With a freshly-prepared bath, it may happen that surfaces already gilt will lose their gold by changing their positions.

This is a sign that the bath contains too much cyanide, and too little gold, or that the electric current is too weak.

(/) When the deposit obtained in cold baths is unsatisfactory in appearance, although the quantity is sufficient, the proper shade may be imparted by: - (1) The gilt article is steeped in a solution of nitrate of binoxide of mercury, until it has become white. It is heated afterwards to volatilise the mercury, and scratch-brushed. (2) Place the article in concentrated sulphuric acid, then heat it until abundant white fumes are disengaged, throw it, still hot, into a weak pickle of sulphuric acid. In this case, the acid has destroyed the organic impurities which may exist in the deposit, and reduces the subsalts of gold to the metallic state. (3) Smear the article with a thick paste of water and powdered borax, or with lime biphosphate of the consistency of honey, fend heat until igneous fusion takes place. Then put the article into dilute sulphuric acid, which dissolves the borax or the biphosphate, and leaves the gold with its natural bright lustre. When, after scratch-brushing small gilt articles, their colour is not entirely satisfactory, it may be improved by plunging the articles again into the bath but for an instant, and then immediately into boiling water. For gilding German silver, the solution should be worked at rather a low temperature, and with a less surface of anode.

The solution should be just so weak in precious metal, that the German silver will not precipitate the gold without the aid of the battery; otherwise the deposit will take place so rapidly that the gold will peel off when being burnished or scratch-brushed.

(g) Gold electroplating in hot baths is more regular, more rapidly obtained, and possesses a deeper shade than that by cold baths. Crystallised soda phosphate, 21 oz.; soda bisulphite, 3 1/2 oz.; pure potassium cyanide, 1/3 oz.; pure gold, transformed into chloride, 1/3 oz.; distilled water, 2 1/5 gal. This is satisfactory for electrogilding silver, bronze, and other alloys rich in copper.

(A) For gilding wrought and cast iron and steel directly, without a previous coat of copper, the bath is modified as follows: - Distilled water, 2 1/5 gal.; soda phosphate, 17 1/2 oz.; soda bisulphate, 4 1/2 oz.; pare potassium cyanide 1/5 oz.; gold transformed into chloride, 1/3 oz. The proportion of gold indicated is that of the metal employed and it is not necessary to mind the weight of the chloride, if the proper amount of gold is dissolved in aqua regia: - 10 parts metallic gold correspond to about 18 of neutral chloride, or to 22 of acid chloride such as is usually sold. Steel articles, after cleansing by alkalies, must be passed rapidly through a very dilute 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 current.

Put four-fifths of the distilled water into a porcelain dish, or an enamelled cast-iron kettle, heated over a charcoal stove, and dissolve in it, by the aid of stirring, the crystallised soda phosphate. When this is entirely dissolved, remove the liquor from the fire, filter if necessary, and allow it to cool off. Place the gold in a glass flask, with 1/2 oz. pure nitric acid and 1 oz. pure hydrochloric acid. Heat slowly until the gold has dissolved, and then more rapidly to expel the excess of acid. There should remain a thick liquid of a blackish-red colour. Remove the flask from the fire, and by cooling the contents form a brown-red crystalline mass. The cooling is important. Dissolve in a porcelain, dish, in half the remaining water, the soda bisulphite and the potassium cyanide. Then dissolve the neutral gold chloride in the remaining water, and pour it slowly, stirring with a glass rod, into the cold solution of soda phosphate; add the solution of bisulphite and cyanide. The whole liquor soon becomes colourless; the bath is then ready.

If the gold chloride were thrown into the solution of soda phosphate while hot there would be danger of a partial reduction of the gold in the form of a metallic powder.