a porous cell placed inside of the mould, which is connected with the zinc, another deposit of copper takes place in the cavity. When the thickness of the metal is sufficient, the mould or first deposit is peeled off, and we obtain the copper reproduction of the object in high relief. This process is expensive, but gives sure results with large patterns with parts in pronounced relief. With small, or narrow objects, or those of which the reliefs are very sinuous, Roseleur recommends sectional moulds, although the seams are always seen and require careful retouching.

Lenoir's Process-Galvanoplastic Method for Originals in High Relief with Gutta-Percha Moulds.

It is proper to insert in this place the galvanoplastic method for articles in high relief, with gutta-percha moulds, invented by Lenoir, to whom the arts are indebted for several valuable discoveries.

Lenoir had been impressed by the enormous labor required for finishing up a bronze coming from the foundry: retouching, filling up, scraping, smoothing, and chasing were as many causes for rendering the object accessible only to the favored few. Moreover, after a passage through so many hands, the reproduction was but the shadow of the work of the master. He was also well acquainted with the difficulty of soldering together the various parts of galvanoplastic productions, so as to form with them a bust, a group, or a statue.

The problem to be solved was to obtain from a perfect pattern as many galvanoplastic copies in one piece as desired, and with such accuracy that the artist to whom the model was due could not distinguish it from the reproduction.

We shall see by what series of processes, one more in

genious than the other, Lenoir succeeded in solving the problem.

Let us take, for instance, a statue (Fig. 157). We begin by making with gutta percha a mould in several

Fig. 157.

be

pieces, which, by means of proper marks, may united together, and form a perfect hollow mould of the original. All these parts are carefully coated with plum bago.

This having been done, a skeleton (Fig. 158), is made with platinum wire, following the general outline of the model, but smaller than the mould, since it must be sus pended in it without any point of contact.

If the skeleton thus prepared is inclosed in the metallized gutta-percha mould, and the whole is immersed in the galvanoplastic bath, it will be sufficient to connect the inner surface of the mould with the negative pole of the

battery, and the skeleton of platinum wires (which should have no points of contact with the metallized surface of the mould) with the positive pole, in order to decompose

the solution of sulphate of copper which fills the mould. When the metallic deposit has reached the proper thic ness, the gutta-percha mould is removed by any convenien process, and a faithful copy of the original will be гергоduced, which may be finished at a very small expense. But though the explanation of the process is very sim ple, its execution is not so easy, for which reason we shall examine the precautions devised by the inventor to insure success.

Fig. 159.

First, it is very difficult to ascertain that the skeleton anode is nowhere in contact with the inclosing mould. In order to avoid such contact. Lenoir wraps with a spiral of India-rubber thread all the external parts of the platinum anode. This rubber coating prevents the contact of the metal with the mould. Fig. 159 represents the manner in which the spiral of India-rubber thread runs round the platinum wire.

Second, notwithstanding all these precautions, it was still possible that, with the increase of the deposit of cop per, which would reduce the distance between the mound and the anode, the latter and the deposit would come i contact, and hence stop the operation without manifesti any exterior sign to attract the attention of the operator

This was an objection sufficiently serious to render the whole process entirely useless. For, if in a vat hold ing many moulds, one point of contact were established between the two poles (mould and skeleton), the curr of the battery would be short-circuited and escape at tha place, and the deposition would cease entirely.

In order to obviate this possible inconvenience, Lenc has devised the following process:

All the moulds of the same bath are supported by hooks suspended from a metallic rod. These hooks hav

no contact with the black-leaded surfaces of the moulds, which are connected with the negative pole by means of metallic wires terminated above the liquid by other iron wires as fine as hair. The connecting wires of the skeleton anode pass through the same opening as the negative conductor, but without contact, and are united to the positive pole (Fig. 160).

It results from this disposition that, as long as there is no contact between the skeleton and the interior of the mould, the electric current finds sufficient passage through the several slender iron wires which connect the moulds with the battery; but, if any contact takes place, the electricity escapes at that point, and, being too abundant for the small section of the iron wire, it heats and burns