the four following formulæ, however, are especially recommended by Roseleur.

These formulæ are set down in the order of their value,

the first one being the most highly esteemed.

This formula is equally satisfactory for the rapid electrogilding of silver, bronze, copper, German-silver, and other alloys rich in copper. On the other hand, for gilding wrought and cast iron and steel, directly, that is to say, without a previous coating of copper, the formula should be modified as follows:

If, on the contrary, we wish to gild zinc, tin, lead, antimony, or the alloys of these metals, it is always preferable to give them a previous coating of copper, or, at least, to begin the gilding in a hot gold electro-bath, nearly spent,

* It should be well understood, once for all, unless the contrary is expressly stated, that the proportion of gold indicated in all these formula is that of the metal employed, and not that of the resulting salt. It is not necessary, therefore, to consider the weight of the chloride when the gold has been dissolved in aqua regia. For the information of those who buy the chloride of gold already prepared, we will say that 10 parts of metallic gold correspond to about 18 parts of neutral chloride, or to 20 or 22 parts of acid chloride, such as is sold by chemi

cal dealers.

and to scratch-brush the articles carefully. The gilding is completed in a fresh hot bath, with quite an energetic

current.

PREPARATION OF THE HOT ELECTRO-GILDING BATH BY THE PRECEDING FORMULA.

We proceed as follows:

1. Into a porcelain dish, or an enamelled cast-iron kettle, heated over a charcoal furnace, introduce 800 parts of rain (or distilled) water, and stir into it the 60 parts of crystallized phosphate of sodium. When the salt is entirely dissolved, remove the vessel from the fire, filter if necessary, and allow the solution to cool off.

2. Introduce into a glass flask, 1 part of finely laminated gold, with 1 parts of pure nitric acid and 2 parts of pure hydrochloric acid. Heat slowly until all the gold has dissolved, and then more rapidly to expel the excess of acid. There should remain in the flask a syrupy liquid of a blackish-red color. Then remove the flask from the fire, and allow the contents to cool, when it should form a brown-red crystalline mass.

3. Dissolve in a porcelain dish, in 100 parts of water, 10 parts of bisulphite of sodium and from to 1 part (according to circumstances) of pure cyanide of potassium.

4. Then dissolve the neutral chloride of gold in the remaining 100 parts of water, and pour it slowly (stirring all the while with a glass rod), into the cold solution of phosphate of sodium. This mixture acquires a greenishyellow tinge; and without losing time, pour into the mixture the solutions of bisulphite and of cyanide. The resulting liquid soon becomes colorless, and the gilding bath is ready.

If, instead of allowing the solution of phosphate of sodium to cool off, the chloride of gold were poured into

it while hot, there would be danger of a partial reduction of the gold, in the form of a brownish-red powder.

To sum up, the proper preparation of this bath requires :

1. The solution of 60 parts of phosphate of sodium in 800 parts of water, which should be allowed to cool off; 2. The solution, in 100 parts of water, of the chloride resulting from the treatment of 1 part of gold with aqua regia, and its gradual mixture with the former solution;

3. The solution in the remaining 100 parts of water, of 10 parts of bisulphite of sodium, and 1 part of pure cyanide, and the mixture of this last solution with the preceding ones.

Roseleur deprecates the practice of many gilders in substituting ordinary for distilled water, then dissolving all the salts together except the chloride of gold, and adding the last to the liquid while the latter is still hot. This method is certainly more rapid, but always produces turbid baths, the working of which is uncertain.

The hot electro-gilding baths are kept in porcelain dishes for those of small dimensions, but, with large volumes, enamelled cast-iron kettles are employed. They are worked at a temperature which may vary from 110° to 175° Fah.

Small articles, like brooches, bracelets, and trinkets in general, are kept in the right hand with the conducting wire, and immersed and constantly 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 gilded.

Large pieces are suspended from one or more brass rods, and immersed in the bath along with the platinum anode and are allowed to remain motionless.

The gilding is very rapid, and a sufficient thickness is obtained after an immersion of a few minutes.

The shade of the gold deposit is modified by dipping the platinum anode more or less into the liquid. If it dips but a little, relatively to the surface of the articles, the gilding is pale; by immersing it more and more, the shade will become deeper and deeper, until it is decidedly red.

Generally, the gilders of trinkets nearly exhaust their baths; and as soon as they cease to give satisfactory results make a new one, and keep the old bath for colored golds, as shall be explained further on, or for beginning the gilding of articles which are scratch-brushed and then finished in a fresh bath. On the contrary, those who gild large pieces maintain the strength of their baths by successive additions of chloride of gold, or, what is better, of equal parts of fulminate of gold 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, after having served to gild many articles of copper or of silver.

As a general rule, it is preferable to replace an impoverished bath by a fresh one, instead of keeping up its strength by additions of metal.

Articles of copper, or its alloys, should be perfectly cleansed, and, according to the judgment of the operator, will be passed, or not, through a very diluted solution of nitrate of mercury. Silver requires to be well cleansed by dipping, and perfectly scratch-brushed. For this latter metal, the gilding should be strong, in order to prevent the corners and parts in relief from soon becoming white from wear; and, when practicable, a good precaution will be to give it a preliminary coating of copper or brass, or at least a first gilding in an old bath.

All the substances except the chloride of gold may be dissolved together, and if necessary filtered; then the solution of the chloride of gold is added. This bath is used at a temperature of from 110° to 140° Fah., and produces a very fine gilding, but it requires quite an intense electric current. It is not adapted for the direct gilding of iron or steel.

The first three salts are dissolved in hot water, and the solution is filtered; after cooling, the gold solution is added, and the whole brought again to a boil for half an hour, taking care to replace the evaporated water.

Dissolve the chloride of gold in the whole of the water, and add the cyanide little by little. This rapidly dissolves and forms a completely colorless liquid.

Of this bath, Roseleur remarks, it may be employed