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The pile was charged with sulphate of copper and marine salt of 10° of weighed salt. We employed 6 elements of 2 decimetres on each side.

We operated at first on two plates of polished silver of 5 centimetres on a side; the surface requiring gilding was then 50 square centimetres.

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Thus, as we see, nothing is more regular than these numbers, the differences being probably attributable rather to the uncertainty of the experiments and of the weights than to the process itself. As

to the influence of temperature, it is manifest, and the rapidity of the deposit is augmented in proportion as the temperature of the solution is increased.

The nature of the metal probably exercises but little influence, provided it is a good conductor. The following experiment seems at least to prove it; it will also be confirmed by other instances.

We have gilded, in fact, a plate of brass of 5 centimetres a side, with the same elements, the same liquid, and in operating in precisely the same circumstances of temperature as for the plate of silver which served for our last experiment. We shall see that the weight of gold deposited is shewn to be exactly the same.

Plate of Brass of 5 Centimetres on a side.-Temperature of Liquid,

15° cent.

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We have remarked, in these kinds of trials, that the first immersion was often less efficacious than the following immersion. This circumstance is explained by the difficulty which is always experienced in preparing the metal so as to render it capable of being moistened on every part of its surface. Once overcome, however, this cause of error does not occur again in the succeeding proofs. Almost every one having explained it by an accidental circumstance, there remained some doubts on our minds, which we submit to philosophers. They will have to certify whether this peculiarity is not governed by a certain resistance on the part of one metal to deposit itself on another metal, which resistance disappears when it is only required to be deposited on itself.

In a word, in many of our essays, when gold, for example, was deposited on gilded plates, the weight of the deposit was always the same for a given time, whilst in the first immersion, where gold had to be deposited on silver or bronze, the weight of the deposit was less.

Silver Plating. All that we have just advanced on the applications of gold, it is necessary to repeat in those of silver. M. de Ruolz has equally attained, by means of a cyanuret of silver dissolved in cyanuret of potassium, the application of silver with the greatest facility.

Silver may be applied on gold and on platinum, as a matter of taste or ornament.

It may be also very well applied on brass, bronze, and copper, in order to replace plate.

Pewter, iron, and steel may also easily be silvered.

The application of silver on copper or brass is accomplished with such a facility, that it is destined to replace all the methods of plating by hand, of plating by the humid method, and even, in many cases, the fabrication of plate. In fact, silver may be applied in thin pellicles, as it is practised to guarantee from oxydation a crowd of objects of ironmongery, and in coats as thick as it may be thought proper, in such a manner as to preserve them from wear. This is one of the applications which has most attracted the attention of your Commission.

For the purposes of chemists, we have proved that a capsule of brass, silvered, may be substituted for a silver capsule, as it has resisted at the point of fusion the action of hydriodated potash; a proof that it would not be necessary to repeat too often, since silver is dissolved in potash. From whence it evidently results that it will be of some interest to see how far we may extend the application of these new processes to the preservation of balances, to that of physical machines, to the preservation of the utensils employed in our households, among our confectioners, or of the apothecaries, and for all the preparations of aliments or of acid medicines.

Silver may be very well applied on brass. It furnishes also the means of driving away, with great facility, the disagreeable odour of covers of brass, by giving them, besides, the aspect and all the exterior properties of covers of silver. It will be, without doubt, one of the most important circumstances of the processes which occupy our attention, if in the place of brass, as the body of the piece, we can substitute another metal: we need only substitute another metal more economical and more solid. It acts upon iron, and even on cast iron. These metals, fashioned into covers and faced with a layer of silver, will become popular in France, by their easy sale; objects which are already common in England. There are manufactured, by other processes, much dearer and far less perfect, at Birmingham, many covers of iron silvered, and their use is common in most families in England. The experiment is then made, and the Commission has seen with the greatest interest the processes of M. de Ruolz furnish a plating, equal and perfect, on iron and cast steel, as the objects laid before the Academy prove.

Still recognising the fact that pewter may be silvered without difficulty, it seemed more convenient to the true interests of the finisher to make the covers of iron or cast metal silvered, and to reserve the silvered pewter for those pieces destined for less frequent using, and especially for the pieces obtained by the more delicate

moulds.

Silver acts like gold when the solutions are reduced in the cyanurets, at least if we judge by the following experiments, where the

K

same pile was made use of as for gold, charged in the same manner, and placed in the same circumstances of temperature, but where we made use solely of 4 elements instead of 6.

The liquid employed for silvering contained 1 gramme of dry cyanuret of silver dissolved in 100 grammes of water containing 10 grammes of yellow ferro-cyanuret of potassium.

Temperature of the Liquid, 45° cent.-Plate of Red Copper of 5 Centimetres a side.

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Temperature of Liquid, 30° cent.-Plate of Red Copper of 5

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Temperature of the Solution, 30° cent.-Plate of Brass of 5

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Thus, the same as with gold, silver applies itself with regularity, in weights proportionate to the duration of the immersions, and without the nature of the metals which we are silvering exercising any appreciable influence. This will nevertheless manifest itself in fact, but only at the moment of the first immersion, and it ought to disappear in the succeeding immersions.

As we might besides expect, the precipitation of silver is rather slower than that of gold.

To Platinize. At first sight, after the analogy which exists between platinum and gold in many respects, we might have supposed that platinum is applied with as great facility as gold on the different metals already cited. The result, however, has presented serious difficulties for a long time, by the slowness with which it obeys the action of the pile. It was found necessary, with the solutions in the cyanurets, for example, to give to the experiment a duration of one hundred or two hundred times longer for platinum than for silver or gold of equal thicknesses.

But in using double chloride of platinum, and of potassium dissolved in caustic potash, we obtain a liquor by which we are enabled to platinize with the same facility, and the same promptitude, as when we are operating with gold or silver.

We will not insist on the very varied applications which platinum may receive in this new direction. The chemists will thus have the means of procuring large capsules of platinized brass, which will unite with cheapness all the necessary resistance to acid or saline solutions.

Armourers will put to profit, under different forms, this means of preservation of the oxydable or sulphurable metals which are used in the fabrication of arms; jewellers will thereby be enabled to introduce platinum in their decorations; those occupied in horology will find therein an excellent agent to cover with a very durable varnish those pieces the alteration of which they fear.

As the platinum, thus applied, may be obtained from the burnt solution of the ore of platinum, and as the metals which accompany the platinum are scarcely at all prejudicial to the process, we see that the platinum in this case costs hardly so much even as silver itself, for experiment proves that a thickness of the least moiety is a sufficient preservation. The result evidently is, that the uses of platinum, hitherto too numerous for the possible production of this metal, may be extended without limits, and will offer certain facilities for its use.

The fabricators of chemical products will have, without doubt, frequent occasions to avail themselves of the use of platinum under these new forms, and it will be very desirable, for example, if they can replace their cucurbites of platinum by those of iron platinized, used in the concentration of sulphuric acid. Where the use of cucurbits of glass is adhered to in many processes in the manufactures, they would be abandoned without doubt; thereby exposing, in the

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