The

possess something about them worthy of your attention. strong resemblance that the burr on both sides of the coin have for the burr produced by the electrical discharge through paper or card, has induced me to draw your attention to the fact. If you think it bears any resemblance in effect, you will greatly oblige me by giving an opinion on the subject.*

It appears to me the resistance that the bird shot meet with at the first moment of impact against the copper coin, causes a sudden splash or disruption of the surface first struck, producing the burr on that surface, and that the shot still continue on with the greater part of the original momentum given by the powder in the first instance, until they pass through the copper coin, producing the burr on the opposite side, after the manner of a punch when driven through metals by any ordinary force. Water also, when ejected with force on the ground, produces similar effects as respects the first surface acted on.

* The specimens with which Mr. Marsh has favoured us, are very striking instances of burrs being produced on both sides of bodies when perforated in one direction only; and shew the futility of all attempts to prove the existence of two electric fluids from the electric burr experiment.-EDIT.

Report on the New Processes introduced in the Art of Gilding. By M. M. ELKINGTON and DE RUOLZ.†

A new art of the highest importance, for its tendency is, generally, to render the enjoyments of luxury more reasonable, has just had birth given to it in France, at least it has there received unexpected developements. It is the art of applying at will the metals which offer the greatest resistance, or the most beautiful, in layers as thin as those of varnish, or in thick layers, as may be required, on the objects formed of other metals less dear and more durable than they are.

Thus objects in iron, in steel, that is to say tenacious, hard, or sharp, but oxydable in the air, may, whilst they at the same time preserve their original properties, become unalterable by means of a varnish of gold, of platina, or silver, so light and so thin that their price will scarcely be increased in the least.

Utensils of copper, tin, or brass, which would be dangerous or disagreeable, may receive the same preparation in thicker beds or layers, and thereby become unalterable to the action of the air, inodorous and salubrious in their employment. And as the agent which produces these effects possesses a power without limits, it may be added, that it is not only gold, platinum, and silver which we may apply on some metals, but copper, lead, zinc, nickel, cobalt, &c., which, put under contribution according as the circumstances may require, come in their turn to change the aspect of the objects

↑ Comptes Rendu, December, 1841.

on which we force them to deposit themselves, or to communicate properties useful and novel.

It is enough to say, that the agent which determines these metallic precipitations is no other thing than the pile; but the pile applied to the dissolutions of a suitable nature, and of which, until now, the necessity has not been comprehended for these kinds of

reactions.

We ask the Acadamy, with permission, to dwell some moments on an art which will have for its effects an almost certainty to destroy all those trades so dangerous as the gilding with mercury; which will transport, even into the most humble chamber, the agreeable and salubrious usage of plated utensils; which will permit the application of silver gilt to a crowd of objects of common usage, and which, by that, even provoking a considerable deperdition of the precious metals, will reanimate the exploration of the mines of silver-will enhance the abated value of this metal, and make an equilibrium in the excess of production, which in this sense has manifested itself for a long time in so striking a manner.

The Commission formed by the Minister of Finances, M. Lacave-Laplagne for the examination of our moneys, of our monetary trades, and the general melting down again of all our metals in circulation, will then see with pleasure a discovery which tends to correct an inconvenience with which it is itself actively preoccupied, the excessive accumulation of silver in France, which in less than fifteen years has seen its capital of silver doubled, and at least 5-7ths of its capital of gold disappear. But she will see, perhaps, also, with some disquietude, so many causes which menace the situation of our money in circulation-the new processes, the novel forces which industry lays hold of, will add to the means of fraud unknown until the present time. Each of its members will find, we doubt not, in these few words, where we are not, nevertheless, able to express all our thoughts, a grave and profound motive to appeal to all its wishes, and to excite, as much as in it lays, the putting into practice those resolutions which have been for a long time elaborating, and which would have had the power already to place our money in a situation less dangerous for the country, and more in harmony with the actual state of the arts and sciences.

The details into which we are about to enter will render easily comprehensible, in fact, the new conditions in which commerce and the management of the precious metals will be placed, in the presence of an art which enables us to gild, to silver, or to platinize any metallic matter, and to spread them all in such a manner as not to alter the most delicate forms-of an art with which the object permits us to remake the mould, as with the mould it gives the means of reproducing the object; of an art, in fine, where the products are self-obtained, without noise, without preparation, without first expense, without workmanship, and where the least place will suffice for an extended execution of the process.

The Commission knows all the importance of these words; it has maturely weighed them. But it was its duty to awake, now that it is time, and in the presence of an inevitable danger, the solicitude of the administration as well as that of commerce.

The gilding on brass and silver, that which is most practised, is constantly performed, and has been for some years, by means of mercury. After having carefully removed the verdigris from the piece, it is smeared over with an amalgam of gold; it is then passed through the fire; the mercury evaporating, leaves the gold on the surface of the piece. But in the practice of such a process, the workmen, exposed without cessation to the contact with the liquid mercury, or to the action of the vapours of mercury, are exposed in a high degree to the deleterious effects of the poisonous mercurial emanations.

The Academy has always taken particular interest, in the perfecting of this branch of industry, with regard to its effect on health. In 1818, a prize of 3,000 francs, founded by an old gilder on bronze, M. Raorio, was awarded to our colleague, M. D'Arcet, which at this epoch had not been received into its bosom by the chemical section. From that time the Academy has not lost sight of the art of gilding; it has followed all the essays of which it has been the object, with the hope of there finding the solution of a question so worthy of the solicitude of all the friends of this class of artisans.

It is in this spirit that the Commission of the insalubrious arts has just proposed this year to the Academy to recompense the introduction into the arts of the galvanic gilding. The discovery of gilding by the humid method also, which is brought into practice on brass as much in England as in France, is there become the object of an important commerce, as a guarantee of its success and value.

The Commission distinguished the one from the other of these two processes of gilding, for the reason that the first, which depends on the employment of the pile, permits us to obtain the gilding of any thickness, and to gild all the metals, a fact which assimilates it to the process of gilding by the mercurial method; whilst the second furnishes a thin gilding which is not really a good substitute for the gilding with mercury, and which in many cases cannot be applied to the same objects. However, it puts the artisans who practice gilding by the humid method to a scrupulous examination. It has studied the processes with care; it makes them repeat and vary them under its eyes.

But at the moment when it was going to make known its opinion to the Academy, new incidents arose to complicate the question, by giving it proportions and an interest altogether unforeseen.

In fact, the Commission knew of the different publications of documents emanating from M. De la Rive, Professor of Physics, and Correspondent of the Academy, wherein this skilful philosopher made known the results which he had obtained in gilding executed

by means of the pile, in acting on solutions of the chlorate of gold. This process, of which the Commission had comprehended all beforehand, permits the augmentation at pleasure of the thickness of the lamina of gold; but it presents some real inconveniences, due to some difficulties in the execution, and to certain defects of adherence between the gold and the metal on which it is applied. The physical principle, the basis of the new art, once being discovered, it became necessary still to add thereto all the chemical resources necessary to render the gilding solid and brilliant, capable of taking the mat, the burnish, and the colours; in fine, it was necessary above all to render the operation economical.

The Commission were aware, also, of all that which concerned the process of gilding by the humid method, as it is practised by M. Elkington, whether in France or in England, and it had proved that this process could not replace, in a great number of cases, the mercurial gilding. In fact, by the humid method there can only be fixed a quantity of gold so small, and feebly fixed on the surface of the article, that it is impossible by the best gilding by the humid method to attain a thickness at which the worst gilding by the aid of mercury is forced to arrive.

Thus there remained some doubts in the mind of the Commission on the efficacy of the process of M. De la Rive in practice, though it appeared in its nature capable of fulfilling the object proposed by the gilding with mercury, and it remained convinced that, on his side, the process of M. Elkington did not replace the mercurial gilding, wholly constituting a new and very interesting branch of industry. The Commission had believed that they might conclude, from its essays, that the process of M. De la Rive gives a gilding sufficiently thick, but wanting in solidity and adherence; whilst that of M. Elkington, where the adherence is perfect, does not give a thickness which the objects well gilded by the aid of mercury attain. Different meetings of the Commission, to which the representatives of M. Elkington had been invited, have furnished the different members with an opportunity of expressing very plainly their opinion on this point, and no person made known any solution of the difficulty with which we had been preoccupied.

In the mean time, the Academy received from M. de Ruolz a memoir, in which were found descriptions of the processes in which the author, combining the employment of the pile and that of solutions of gold in the alkaline cyanurets, succeeded in obtaining on all the metals a gilding at the same time adhesive, solid, and of a thickness susceptible of being modified at pleasure, from pellicles infinitely small, up to laminæ of several millimetres in thickness. Generalizing his process, M. de Ruolz applied it to gold, to silver, to platinum, and to a number of other metals more difficult of reduction.

This memoir, and the products which accompanied it, had excited the lively interest of the Commission, when the agent of M.

Elkington, at Paris, became very desirous of submitting to the Academy a patent taken out by M. Elkington, and anterior by some days to that of M. de Ruolz. The Commission acknowledged, in fact, with surprise, that this patent existed, that it contained the description of a process for the application of gold having analogy with that of M. de Ruolz, and the Commission have not yet been able to comprehend for what motives he concealed the existence of the patent, which responded victoriously to all its objections, whilst at the same time it could not call in question M. de Ruolz and his processes.

This being the case, its duty was marked out; it was constrained to fulfil it. The proxies of M. Elkington have operated in its presence; M. de Ruolz likewise did the same. Each of them remitted to the hands of the Commission all the documents which they thought proper to be revealed; the analysis of these documents, the recital of their experiments, will put the Academy in a proper position for judging on the value of the processes of the two inventors.

We shall divide this report into three parts. The first is relative to the process by the humid method, such as it is practised in full by M. Elkington; the second will treat on the galvanic process of the same artist; the third, and last, has for its object the processes of M. de Ruolz.

1st.-Gilding by the Humid Method.

The gilding by the humid method is obtained by a very simple process in practice, but the explanation of which does not present itself in a very satisfactory manner to the minds of chemists, and which by that same fact, besides, ought to offer, and does offer, in fact, inexplicable irregularities in its employment.

This process consists in dissolving gold in aqua-regalis, which converts it into a perchloride of gold, and mixing this with a solution of bi-carbonate of potash in great excess, and then boiling the whole for a long period. The pieces of brass, bronze, or copper, well cleared from verdigris, are afterwards immersed in the boiling liquor, and the gilding takes place immediately, a portion of copper of the piece being dissolved to replace the gold which is precipitated.

In a note addressed to the Academy, an English chemist, M. Wright, has made known the results of researches undertaken by him, conjointly with M. Elkington, and from whence was derived a more satisfactory explication of the process than any which has been proposed hitherto.

It results, from their experiments, that the perchloride of gold is not precisely well adapted to the process of gilding; that the protochloride succeeds much better. They explain by that why it is necessary to boil the perchloride of gold so long a time with the