it out rapidly. The galvanoplastic deposit is thus instantaneously stopped upon this mould, though it continues for the others. Moreover, the broken wire shows the opera tor the location of the defect.

The iron wire should be very short, in order to bun out rapidly. A length of a few inches is sufficient.

sulphate of copper will be rapidly transformed into sulHence the necessity of allowing

phuric acid and water.

at the lower part of the mould (under the feet for instance), space for two holes, through which and the opening at the head, left for the passage of the electrode, a free circulation of the liquid in the bath may take place (Fig. 161).

When the operation is completed, the gutta-percha mould is removed, and the skeleton anode forcibly withdrawn. We have then simply to close the three holes in the statue, and to file off the seams left at the junction of the different parts of the mould, in order to have a perfectly accurate copy of the model.

CHAPTER LXI.

DURATION OF THE OPERATION.

THERE are no precise rules for determining the length of time necessary for a galvanoplastic deposit. It depends upon the thickness of the desired deposit, the intensity of the current, the dimensions, and the more or less irregular shape of the object. The article may be removed from the bath when the thin copper deposit has spread all over the mould; but in this case, the film is not sufficiently firm, and is often perforated. Nevertheless, a quantity of these thin and defective deposits are to be met in the trade, and an appearance of firmness is given them by tinning these from the back, and strengthening this filling with tin or other solder. These strengthened objects are sometimes returned to the galvanoplastic bath, in order to cover the solder with a light layer of copper, and make it appear as though the thickness of

the deposit were considerable, whereas its solidity is simply due to the added solder.

for

The firm of Ch. Christofle & Co. employs a process filling with copper solder (copper and zinc) galvanoplas tic reproductions. By this process they are enabled to furnish to the trade an enormous quantity of perfectly finished and durable articles for furniture and cabinet makers' use. Similar objects were previously made of cast bronze or brass, which required trimming, chasing, and other manipulations before being ready for use.

For filling galvanoplastic reproductions with brass solder, their exterior is first covered with clay, plaster of Paris, or Spanish-white mixed with charcoal dust, after which the whole is perfectly dried in the stove-room. This coating is intended to prevent the copper deposit from losing its shape and being oxidized by the action of a high temperature. The interior of the article is then filled with the softest brass solder to be found, and with powdered borax, which are melted by a gas jet or before the blowpipe. All the hollow parts are soon filled with the solder, which imparts to them at least equal firmness and durability as is to be found in cast articles.

CHAPTER LXII.

REMOVING THE MOULD-FINISHING UP THE ARTICLES.

Removing the Mould.

THIS operation consists in separating the galvanoplas tic deposit from the substance of the mould, and it is evident that there will be nearly as many methods of effecting this as there are substances employed.

With a metallic mould the operation is very simple, and it is sufficient, after having removed the useless portions of the deposits with a file, a saw, or otherwise, to pass a card or a blade of horn or ivory between the model and the deposit to effect their separation without injury. The operation is about the same with moulds of plaster of Paris, porcelain, marble, glass, or wood; but it is very difficult to save a plaster mould which has been in the bath, and which is nearly always sacrificed and separated in fragments.

Moulds of wax, stearine, fusible metal, gelatine, or gutta-percha are heated in boiling water or otherwise; their separation, therefore, presents no difficulty.

Finishing the Articles.

The articles separated from the moulds are generally spotted with plumbago, grease, or other still adhering substances, from the moulds. It is usual to heat them, so as to burn out the impurities, and to cleanse them by a more or less protracted immersion in a pickle of diluted sulphuric acid. The heating presents the advantage of rendering the copper deposit softer and more malleable; on the other hand, it may result in injury to the minute details and the fineness of the copy. Therefore, for delicate reproductions, it will be preferable to clean with alcohol, turpentine, gasoline, or benzole, and to rub the surface with a stiff brush. We may finish with a paste of Spanish-white (levigated chalk) in water, which is allowed to dry upon the object before it is wiped off. In this case, should any Spanish-white still remain in the depressions, it may be dissolved in water containing onetenth of its volume of hydrochloric acid, which does not corrode the copper. The operation is completed by rinsing in fresh water, and drying in sawdust, or otherwise.

When it is desired to anneal the articles without injury to their surface, we may plunge them into boiling colza, or linseed oil, or simply grease, which will bear a heat suffi cient for annealing, and will prevent the oxidizing action. of the air. This annealing in fatty substances is especially to be recommended in the case of highly undercut moulds of gutta percha, which may have left part of the substance in the deep recesses of the galvanoplastic copy. The gutta percha is first softened, and then dissolved in the fatty material.

CHAPTER LXIII.

GALVANOPLASTIC OPERATIONS WITH GOLD OR SILVER-GAL VANOPLASTIC BATHS FOR SILVER AND gold.

Galvanoplastic Operations with Gold or Silver. We have said that it is possible to obtain galvanoplastic deposits of gold or silver; but the processes known at the present time are more difficult and less effective than those for copper. The latter metal is obtained by the reduction of simple salts; whereas such operations with gold or silver require baths of double salts, such as the double cyanide of gold and potassium, or the double cyanide of silver and potassium. The sulphate of copper is very soluble and easily reduced; on the contrary, the sulphate of silver is but slightly soluble in water. The sulphate of gold exists only hypothetically. As for the nitrate of silver and the chloride of gold, which are the most soluble salts of these metals, they have been tried

without success.

A very great disadvantage with the galvanoplastic baths