All of these substances should be as pure as possible, and perfectly dry. Cream of tartar is generally dry; but common salt often needs, before or after it has been pulverized, a thorough desiccation, by gentle heating in a porcelain or silver dish, and stirring with a glass rod, or

a silver spoon.

The mixture of the three substances must be thorough, and should be effected at a moderate heat, long protracted.

The graining is the coarser, according as there is more common salt in the mixture; and conversely, it is the finer and more condensed as the proportion of cream of tartar is greater, but it is then more difficult to scratchbrush.

8. The Graining proper.-This operation is effected as follows: A thin paste of one of the above mixtures, with

of the molecules which injures it for the subsequent operation of graining.

At the present time, the majority of operators, instead of preparing their graining silver, prefer buying the Nuremberg powder, which is produced by grinding a mixture of honey and silver foil with a muller, upon a ground glass plate until the proper comminution is obtained. The silver is separated by dissolving the honey in boiling water, and washing the deposited metal on a filter, until there is no remaining trace of honey. The silver is then carefully dried at a gentle heat.

This silver, like bronze powders, is sold in small packages weighing about an ounce.

water, is spread by means of a spatula upon the articles. attached to the cork. The cork itself is placed upon a platter, holding it with the left hand. An oval brush (Fig. 99), with close bristles is held in the right hand, with which the pieces are brushed in every direction, turning both the brush and the sheet of cork all the while. A fresh quantity of the paste

Fig. 99.

is added two or three times, and used in the manner indicated. The more the brush and the cork are rotated, the rounder becomes the grain, which is a good quality; and the more paste added, the larger the grain.

Watchmakers generally require a fine grain, circular at its base, pointed at its apex, and close, that is to say, a multitude of juxtaposed, diminutive cones. Sometimes, however, a larger grain may make a better appearance; but this will depend on the nature and the size of the articles.

Fig. 100.

9. When the desired grain is obtained, the pieces are washed and then scratch-brushed, with brushes of very fine brass wire. (Fig. 100.) As these wires are very stiff and springy, they will, when cut, bind and turn in every direction, and no work can be done with them. It is therefore absolutely necessary to anneal them more or less upon an even fire. An intelligent worker will always have three scratch-brushes, annealed to different degrees: one which is half soft, or half annealed, for the first operation of uncovering the grain; one harder, or little annealed, for bringing up the lustre; and one very soft, or fully annealed, used before gilding for removing the scratches which may have been made

by the preceding tool, and for scratch-brushing after gilding. Of course, the scratch-brushing operation, like the graining proper, should be done by giving a rotary motion between the fingers both to the tool and the cork. After a good scratch-brushing, the grain, seen through a magnifier, should be regular, homogeneous, and with a uniform lustre all over. Decoctions of liquorice, soapwort, or Panama wood, are employed in this operation.

It frequently happens that the same piece is composed of both copper and steel, and this latter metal requires to be preserved against the action of the cleansing acids and of the graining mixture, by applying a stopping-off varnish.

The operation consists in covering the pinions and other parts of steel with a fatty composition, which is sufficiently hard to resist the tearing action of the. bristle and wire brushes, and sufficiently insoluble in the alkalies of the gilding bath to remain unaffected.

The formula of this composition is as follows:

Yellow wax

Translucent resin

Red sealing-wax (extra fine)

Impalpable peroxide of iron (English polishing
rouge)

The resin and sealing-wax are melted together in a porcelain dish upon a water-bath, whereupon the yellow wax is added. When the whole is thoroughly fluid, the rouge is gradually added, and stirred into the mass with a wooden or glass rod. The heat is then removed, but the stirring should be continued until the mixture becomes solid, otherwise all the oxide of iron will fall to the bottom of the dish.

Flat parts which are to receive this varnish are slightly

heated, and then covered with the above mixture, which melts and is easily spread. For covering steel pinions, which generally form cylindrical projections upon the face of the wheels, a species of stylus of brass or copper is employed, having a wooden handle. (Fig. 101.) The metallic extremity of this tool is heated over an Fig. 101. alcohol lamp, and a small quantity of varnish is taken up with it. The composition soon melts, and, by turning the tool around the steel pinion, this becomes coated. Before fastening the pinion upon the cork, a small cavity is dug in the latter, in which the pinion rests. The remainder of the operation is conducted as with the other parts of the watch movements. Nevertheless, it is prudent to use a scratch-brush with long wires, as their flexibility prevents the removal of the composition. When, after gilding, the varnish is to be removed, the parts are plunged into warm oil, or into tepid benzine or turpentine, then into a very hot soap water, or alkaline solution, and lastly rinsed in fresh water. Scratch-brushing, and drying in warm sawdust of white wood, terminate the operation.

The pinions are cleaned out and polished by passing between them small pieces of very soft white wood, the friction of which is sufficient to restore to the steel its primitive lustre.

The gilding of those parts composed of copper and steel requires the greatest care, since the slightest rust will destroy their future usefulness. Should some gold have become deposited upon the steel, it should be removed by rubbing with a stick of wood and impalpable pumice dust, putty powder, or rouge.

10. Gilding. After the series of preparations above described, we come at last to the gilding, which may be

effected by one of the processes already indicated. Hot baths, of course, should not be employed for those pieces covered with the varnish. The following is a minute. description of this process as employed at Besançon, and which, according to Roseleur, gives good results.

Four parts of finely laminated and pure gold, first heated to redness in order to destroy any organic matter that may be present, are dissolved in a glass flask in a mixture of six parts of pure nitric acid, and twelve of pure hydrochloric acid. When the gold is dissolved, and the excess of acids has been evaporated, leaving in the flask a dark-red, nearly syrupy liquid, the whole is removed from the fire and allowed to cool. The chloride of gold is then dissolved in fifty or sixty parts of distilled water, and poured into a large glass vessel. It is then diluted with about five hundred parts of distilled water, and an excess of pure ammonia is added, which precipitates the gold in the state of a yellowish powder of fulminate of gold, which is highly explosive when dry. A sufficient quantity of ammonia has been added, when a new quantity of this reagent, being added to the supernatent liquid, does not produce any turbidity, or precipitate. The clear liquid is decanted and saved. The precipitate is then collected upon a small filter, previously wetted with distilled water, and there washed with distilled water until all ammoniacal odor has disappeared. The filter, with its contents, is then transferred to a glass or porcelain vessel containing a solution of twelve parts of cyanide of potassium in one thousand of water, which rapidly dissolves the gold and leaves the filter. The solution is filtered anew, boiled for fifteen to twenty minutes, filtered again, and left to cool. The bath obtained is excellent for gilding the most delicate watch works, under