of potassium or sodium, which, until recently, were extolled by a few rule-of-thumb practical men. This simply proves that they were not acquainted with, or did not know how to use, the pyrophosphates.

The bicarbonate bath is prepared by mixing in a cast-iron kettle, turned clean and smooth inside on the lathe, and gilded by protracted ebullition therein, of old or nearly spent gilding-baths—

The whole is boiled for at least two hours, fresh water being added to replace that lost by evaporation. A part of the gold, in the form of a violet-black powder, will be found to have been precipitated, and the bath will require to be cooled and decanted. It is again boiled, and the gilding is proceeded with, in the same manner as previ ously indicated, except that the mercurial solution should be more diluted than is customary with the pyrophosphate baths..

The operation should be arrested when about half of the gold in the bath has been deposited. The remainder goes to the spent liquors from which the gold is subsequently regained.

If we now compare the formula of these two baths, and consider the dilution of the one and the concentration of the other; the rapidity of operation in the first, and the loss of time occasioned by the second; the facility of using all the gold dissolved by the pyrophosphate, and the impossibility of utilizing a great proportion of that in the bicarbonate; we must acknowledge that there is no possible

*This weight is that of the metallic gold, and not that of the chloride resulting from the treatment with aqua regia.

doubt as to which to choose, especially when the quality and the fineness of the products are at least equal. We may add in conclusion, that, at the present time, we know of no gilder employing the above formula, which we have simply recorded as a matter of history.

Immersion-Gilding-Diluted Bath.

Roseleur concludes his list of formulæ for simple immersion gilding, with one, which, on account of the facility with which it may be worked and the great variety of articles for which it may be used, is often employed, notwithstanding the slight durability of the results it furnishes.

This bath should be employed only as a complement to the cleansing process, and as a preliminary operation to a more resistant electro-gilding in a cyanide bath. It is composed of

The whole is brought up to the point of ebullition, and a pale gilding, a mere blush, is obtained even upon imperfectly cleansed articles, and without employing nitrate of mercury.

It is possible, to repeat four or five times, the addition of a small proportion of chloride of gold to this bath, without the addition of other substances. Afterwards, it is maintained at the proper strength by additions of gold and salts in the above proportions, and it lasts for an almost indefinite period.

Such a bath will gild about 4000 parts by weight of small trinkets for each part (by weight) of gold consumed,

whereas a bath of pyrophosphates will gild only about 1000 parts by weight of small articles per unit of gold extracted from the bath.

The gilders of large bronze pieces use this bath for cleansing them before they are taken to the electrobath, and on this account it is called the cleansing or preparing bath.

The following processes for immersion-gilding, from various authorities, may be found useful:—

Gore (Electro-Metallurgy, 129) notices a solution for simple-immersion gilding, at one time extensively used by the Messrs. Elkington. It is prepared by converting one part of gold into neutral terchloride (by the method previously described), dissolving it in a small quantity of water, and adding to it, gradually, thirty-one parts of bicarbonate of potassium. This liquid is then mixed with a solution of thirty parts of the bicarbonate dissolved in two hundred parts of water, and boiled for two hours. The solution, which is yellow at first, becomes green, and is then ready for use. Trinkets of brass or copper, previously cleansed, are immersed in this solution for about half a minute. The bath is used hot. Articles of German-silver, silver, or platinum, must be immersed in contact with wires of copper or zinc.

A similar solution is made by converting five Troyounces of gold into chloride, dissolving this in four gallons of distilled water, adding twenty pounds of pure bicarbonate of potassium, and boiling the mixture for several hours. It is used warm, and articles to be gilded are immersed from a few seconds to one minute.

A solution for gilding articles of silver, described by this and other authors, is prepared by dissolving equal parts by weight of corrosive sublimate and sal-ammoniac

in nitric acid, adding some grain gold to it, and evaporating the liquid to half its bulk. The hot solution is applied to the surface of the silver article.

C. D. Braun's solution for gilding zinc (Chem. News, xxix. 230; Gore, Electro-Metallurgy, 129) is prepared by dissolving sulphide of gold in a solution of sulphide of ammonium, excluded from the atmosphere.

CHAPTER XVII.

GILDING WITH GOLD AMALGAM.

THE older processes admit of the gilding of small copper article's with a thin and adherent coating. One of these ancient methods which we shall now describe, gives results very analogous to those obtained by dipping, just explained.

This operation of gilding with gold amalgam, which is a modification of the method of fire-gilding, which will be shortly described, is performed as follows:

In the centre of a charcoal stove place a crucible holding a small quantity of pure, dry mercury, and when the temperature has reached about 212° Fah., add thereto one-half its weight of gold. Stir with an iron rod, and when the amalgam has acquired the consistency of butter, throw it into cold water, and keep it there for use.

After cleansing the articles to be gilded in aqua fortis, place them in a stoneware pan, and sprinkle them with a very weak solution of nitrate of mercury, taking care to keep the articles in motion all the while, in order to change the positions of their surfaces and cause them to become covered uniformly with a white coating of mercury.

At this point, add to the mass the required quantity of amalgam, and continue to move the articles briskly about. The amalgam spreads rapidly, and after a few minutes will be found to have attached itself uniformly to the surface of the articles. Then rinse in cold water, and transfer the contents of the stoneware pan into a large and deep copper ladle, perforated with numerous small holes, and having a long handle which allows the operator to impart a shaking motion to its contents.

The ladle and its contents are then kept over a live charcoal fire, and the articles are constantly shaken in order to distribute the heat as much as possible. The mercury of the amalgam is soon volatilized, and the gold remains adherent to the articles.

If, instead of a yellow gilding, a red one be desired, the waxing process is now resorted to, which operation consists in pouring upon the articles, still in the ladle and upon the fire, an intimate and fluid mixture of

The articles impregnated with this mixture are constantly agitated. It speedily takes fire and is allowed to burn out, at which instant the whole is thrown into a very diluted solution of sulphuric acid. The waxing is, of course, done only after the complete volatilization of the

mercury.

After coming out of the pickle, the gilding has the ap pearance of ochreous clay, and must be scratch-brushed. Small articles are polished by tumbling along with a lot of copper beads, or the waste from the same, moistened with vinegar-water. The gilded articles and the copper granules, rolling over each other, become polished